From 4bac47a4fdad2fd56f9023eaae9a4be83fe9fced Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Mon, 23 Jun 2025 00:31:53 -0700
Subject: [PATCH 01/27] fix at 256 seconds

---
 mandel.s | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mandel.s b/mandel.s
index 6837e00..714f6b6 100644
--- a/mandel.s
+++ b/mandel.s
@@ -2002,10 +2002,14 @@ update_status:
         countdown_loop:
             lda elapsed_work + 1
             cmp #.hibyte(divisor)
+            beq countdown_lobyte
             bcc countdown_done
+            bcs countdown_inc
+        countdown_lobyte:
             lda elapsed_work
             cmp #.lobyte(divisor)
             bcc countdown_done
+        countdown_inc:
             sec
             lda elapsed_work
             sbc #.lobyte(divisor)

From fd954da47e75a99b0033ec11f0dd145e1d8ab544 Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Mon, 23 Jun 2025 08:17:39 -0700
Subject: [PATCH 02/27] Create map file for convenience

export a symbol and it'll appear in mandel.map
---
 Makefile | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index bd14c7d..711adcd 100644
--- a/Makefile
+++ b/Makefile
@@ -3,7 +3,7 @@
 all : mandel.xex
 
 mandel.xex : mandel.o tables.o atari-asm-xex.cfg
-	ld65 -C ./atari-asm-xex.cfg -o $@ mandel.o tables.o
+	ld65 -C ./atari-asm-xex.cfg --mapfile mandel.map -o $@ mandel.o tables.o
 
 %.o : %.s
 	ca65 -o $@ $<
@@ -15,4 +15,6 @@ clean :
 	rm -f tables.s
 	rm -f *.o
 	rm -f *.xex
+	rm -f mandel.map
+
 

From fab2760394b9b74f07488bc345997fbd9e566389 Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Sat, 28 Jun 2025 13:43:43 -0700
Subject: [PATCH 03/27] refactor countdown as a procedure call

---
 mandel.s | 104 +++++++++++++++++++++++++++++++------------------------
 1 file changed, 58 insertions(+), 46 deletions(-)

diff --git a/mandel.s b/mandel.s
index 714f6b6..cad4e5e 100644
--- a/mandel.s
+++ b/mandel.s
@@ -1991,55 +1991,25 @@ update_status:
     lda FR0 + 1
     sta elapsed_work + 1
 
-    ;jsr IFP
-    ;jsr FASC
-    ;jsr draw_string
-
-    .macro countdown divisor, digits
-        .scope
-            ; count the hours
-            ldx #0
-        countdown_loop:
-            lda elapsed_work + 1
-            cmp #.hibyte(divisor)
-            beq countdown_lobyte
-            bcc countdown_done
-            bcs countdown_inc
-        countdown_lobyte:
-            lda elapsed_work
-            cmp #.lobyte(divisor)
-            bcc countdown_done
-        countdown_inc:
-            sec
-            lda elapsed_work
-            sbc #.lobyte(divisor)
-            sta elapsed_work
-            lda elapsed_work + 1
-            sbc #.hibyte(divisor)
-            sta elapsed_work + 1
-            inx
-            jmp countdown_loop
-        countdown_done:
-            lda digits,x
-            eor #$80
-            sta elapsed_digit
-            lda #.lobyte(elapsed_digit)
-            sta INBUFF
-            lda #.hibyte(elapsed_digit)
-            sta INBUFF + 1
-            jsr draw_string
-        .endscope
-    .endmacro
-
     draw_string_const str_space
-    countdown 36000, digits_space
-    countdown 3600, digits_zero
+    
+    .macro do_countdown divisor, digits
+        ldx #.lobyte(divisor)
+        ldy #.hibyte(divisor)
+        lda #.lobyte(digits)
+        sta INBUFF
+        lda #.hibyte(digits)
+        sta INBUFF + 1
+        jsr countdown
+    .endmacro
+    do_countdown 36000, digits_space
+    do_countdown 3600, digits_zero
     draw_string_const str_h
-    countdown 600, digits_zero
-    countdown 60, digits_zero
+    do_countdown 600, digits_zero
+    do_countdown 60, digits_zero
     draw_string_const str_m
-    countdown 10, digits_zero
-    countdown 1, digits_zero
+    do_countdown 10, digits_zero
+    do_countdown 1, digits_zero
     draw_string_const str_s
 
 skipped:
@@ -2101,3 +2071,45 @@ loop:
     jmp main_loop
 
 .endproc
+
+; digit string in INBUFF
+; divisor X/Y
+; clobbers temp, calls draw_string
+.proc countdown
+    divisor = temp
+    stx divisor
+    sty divisor + 1
+
+    ; count the hours
+    ldy #0
+countdown_loop:
+    lda elapsed_work + 1
+    cmp divisor + 1
+    beq countdown_lobyte
+    bcc countdown_done
+    bcs countdown_inc
+countdown_lobyte:
+    lda elapsed_work
+    cmp divisor
+    bcc countdown_done
+countdown_inc:
+    sec
+    lda elapsed_work
+    sbc divisor
+    sta elapsed_work
+    lda elapsed_work + 1
+    sbc divisor + 1
+    sta elapsed_work + 1
+    iny
+    jmp countdown_loop
+countdown_done:
+    lda (INBUFF),y
+    eor #$80
+    sta elapsed_digit
+    lda #.lobyte(elapsed_digit)
+    sta INBUFF
+    lda #.hibyte(elapsed_digit)
+    sta INBUFF + 1
+    jsr draw_string
+    rts
+.endproc

From 96e0356e578f7c94dd2c5764ecbf59f70dbe29d9 Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Thu, 3 Jul 2025 18:41:24 -0700
Subject: [PATCH 04/27] WIP input handling for coords

experimental output via 32-bits mult, looses precision in conversion
---
 mandel.s | 136 +++++++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 128 insertions(+), 8 deletions(-)

diff --git a/mandel.s b/mandel.s
index cad4e5e..4cc0f39 100644
--- a/mandel.s
+++ b/mandel.s
@@ -126,6 +126,10 @@ KEY_7     = 51
 KEY_8     = 53
 KEY_9     = 48
 KEY_0     = 50
+KEY_PERIOD = 34
+KEY_E     = 42
+KEY_X     = 22
+KEY_Y     = 43
 
 .struct float48
     exponent .byte
@@ -257,6 +261,28 @@ fixed3_13_as_float: ; float48
     .byte $00
     .byte $00
 
+u65536_as_float: ; float48
+    ; 1 << 16
+    ; 65536
+    ; 06 55 36 . 00 00
+    .byte 66 ; exponent/sign - +2 bytes
+    .byte $06
+    .byte $55
+    .byte $36
+    .byte $00
+    .byte $00
+
+fixed6_26_as_float: ; float48
+    ; 1 << 26
+    ; 67108864
+    ; 67 10 88 64 . 00
+    .byte 67 ; exponent/sign - +3 bytes
+    .byte $67
+    .byte $10
+    .byte $88
+    .byte $64
+    .byte $00
+
 sec_per_frame: ; float48 00 . 01 66 66 66 67
     .byte 63  ; exponent/sign - -1 bytes
     .byte $01 ; BCD digits
@@ -403,6 +429,13 @@ elapsed_work:
 elapsed_digit:
     .byte 0
 
+input_col:
+    .byte 0
+input_row:
+    .byte 0
+input_max:
+    .byte 0
+
 ; 2 + 9 * byte cycles
 .macro add bytes, dest, arg1, arg2
     clc ; 2 cyc
@@ -983,6 +1016,66 @@ common:
 
 .endproc
 
+; input in FR0, 32 bits signed 6.26 fixed
+; output in FR0, Atari float
+; clobbers a, x, y, FR0, FR1
+.proc fixed6_26_to_float
+    ; check sign bit! conversion routine is for unsigned
+    lda FR0 + 3
+    and #$80
+    sta temp
+
+    beq positive
+    neg32 FR0
+positive:
+
+    ; save low word
+    lda FR0
+    pha
+    lda FR0 + 1
+    pha
+
+    ; convert high word
+    sta FR0 + 2
+    sta FR1
+    lda FR0 + 3
+    sta FR0 + 1
+    jsr IFP
+
+    lda temp
+    beq positive2
+    ; set float sign bit
+    lda FR0
+    ora #$80
+    sta FR0
+positive2:
+
+    ; high word to FR1
+    ldx #.lobyte(u65536_as_float)
+    ldy #.hibyte(u65536_as_float)
+    jsr FLD1R
+    jsr FMUL
+    jsr FMOVE
+
+    ; convert low word
+    pla
+    lda temp + 1
+    pla
+    lda temp
+    jsr IFP
+
+    ; combine
+    jsr FADD
+
+    ; scale
+    ldx #.lobyte(fixed6_26_as_float)
+    ldy #.hibyte(fixed6_26_as_float)
+    jsr FLD1R
+    jsr FDIV
+
+    rts
+.endproc
+
 ; input in FR0, Atari float
 ; output in FR0, 16 bits signed 3.13 fixed
 ; clobbers a, x, y, FR0, FR1
@@ -1603,7 +1696,7 @@ number_keys:
     beq five
     cpy #KEY_6
     beq six
-    jmp skip_char
+    jmp letter_keys
 
 one:
     ldx #0
@@ -1622,7 +1715,21 @@ five:
     jmp load_key_viewport
 six:
     ldx #5
-    ; fall through
+    jmp load_key_viewport
+
+letter_keys:
+    cpy #KEY_X
+    bne not_x
+    jsr input_x
+    jmp load_key_viewport
+not_x:
+    cpy #KEY_Y
+    bne not_y
+    jsr input_y
+    jmp load_key_viewport
+not_y:
+    jmp skip_char
+
 load_key_viewport:
     jsr load_viewport
     ; fall through
@@ -1632,6 +1739,23 @@ done:
 
 .endproc
 
+.proc input_x
+    ldx #col_x
+    ldy #1
+    jsr input_number
+
+
+    rts
+.endproc
+
+.proc input_y
+    rts
+.endproc
+
+.proc input_number
+    rts
+.endproc
+
 .proc clear_screen
     ; zero the range from framebuffer_top to display_list
     lda #.lobyte(framebuffer_top)
@@ -1679,9 +1803,7 @@ zero_byte_loop:
     draw_string_const str_x
 
     copy32 FR0, ox
-    shift_round_16 FR0, 3
-    copy16 FR0, FR0 + 2
-    jsr fixed3_13_to_float
+    jsr fixed6_26_to_float
     jsr FASC
     jsr draw_string
 
@@ -1690,9 +1812,7 @@ zero_byte_loop:
     draw_string_const str_y
 
     copy32 FR0, oy
-    shift_round_16 FR0, 3
-    copy16 FR0, FR0 + 2
-    jsr fixed3_13_to_float
+    jsr fixed6_26_to_float
     jsr FASC
     jsr draw_string
 

From f2a6af0995512835bae7e6ecd094e15ef5115fc3 Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Thu, 3 Jul 2025 18:43:10 -0700
Subject: [PATCH 05/27] Replace the not-enough-precision 32 bit to float impl

keep the proc though to encapsulate it but uses the older
logic of rounding down to 3.13 first
---
 mandel.s | 79 +++-----------------------------------------------------
 1 file changed, 4 insertions(+), 75 deletions(-)

diff --git a/mandel.s b/mandel.s
index 4cc0f39..a97d6e3 100644
--- a/mandel.s
+++ b/mandel.s
@@ -261,28 +261,6 @@ fixed3_13_as_float: ; float48
     .byte $00
     .byte $00
 
-u65536_as_float: ; float48
-    ; 1 << 16
-    ; 65536
-    ; 06 55 36 . 00 00
-    .byte 66 ; exponent/sign - +2 bytes
-    .byte $06
-    .byte $55
-    .byte $36
-    .byte $00
-    .byte $00
-
-fixed6_26_as_float: ; float48
-    ; 1 << 26
-    ; 67108864
-    ; 67 10 88 64 . 00
-    .byte 67 ; exponent/sign - +3 bytes
-    .byte $67
-    .byte $10
-    .byte $88
-    .byte $64
-    .byte $00
-
 sec_per_frame: ; float48 00 . 01 66 66 66 67
     .byte 63  ; exponent/sign - -1 bytes
     .byte $01 ; BCD digits
@@ -1016,63 +994,14 @@ common:
 
 .endproc
 
+; rounds to 16-bit first!
 ; input in FR0, 32 bits signed 6.26 fixed
 ; output in FR0, Atari float
 ; clobbers a, x, y, FR0, FR1
 .proc fixed6_26_to_float
-    ; check sign bit! conversion routine is for unsigned
-    lda FR0 + 3
-    and #$80
-    sta temp
-
-    beq positive
-    neg32 FR0
-positive:
-
-    ; save low word
-    lda FR0
-    pha
-    lda FR0 + 1
-    pha
-
-    ; convert high word
-    sta FR0 + 2
-    sta FR1
-    lda FR0 + 3
-    sta FR0 + 1
-    jsr IFP
-
-    lda temp
-    beq positive2
-    ; set float sign bit
-    lda FR0
-    ora #$80
-    sta FR0
-positive2:
-
-    ; high word to FR1
-    ldx #.lobyte(u65536_as_float)
-    ldy #.hibyte(u65536_as_float)
-    jsr FLD1R
-    jsr FMUL
-    jsr FMOVE
-
-    ; convert low word
-    pla
-    lda temp + 1
-    pla
-    lda temp
-    jsr IFP
-
-    ; combine
-    jsr FADD
-
-    ; scale
-    ldx #.lobyte(fixed6_26_as_float)
-    ldy #.hibyte(fixed6_26_as_float)
-    jsr FLD1R
-    jsr FDIV
-
+    shift_round_16 FR0, 3
+    copy16 FR0, FR0 + 2
+    jsr fixed3_13_to_float
     rts
 .endproc
 

From b46e6fb343e425985f53f868f1dbe4e3f6c0e384 Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Mon, 1 Sep 2025 12:28:33 -0700
Subject: [PATCH 06/27] fix typo on stub x/y inputs

was accidentally falling through to the load
a viewport from a keypress thingy which was
not needed here
---
 mandel.s | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mandel.s b/mandel.s
index a97d6e3..5edcbce 100644
--- a/mandel.s
+++ b/mandel.s
@@ -1650,12 +1650,12 @@ letter_keys:
     cpy #KEY_X
     bne not_x
     jsr input_x
-    jmp load_key_viewport
+    jmp done
 not_x:
     cpy #KEY_Y
     bne not_y
     jsr input_y
-    jmp load_key_viewport
+    jmp done
 not_y:
     jmp skip_char
 

From 29cd3d968fbff768c23959fab2f6addcaff8ccfe Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Sat, 6 Sep 2025 19:53:25 -0700
Subject: [PATCH 07/27] Shaves 3 seconds off initial view runtime on XE :D

Instead of relying solely on the JMP thunks added to
imul16_func and sqr16_func, three call sites within the
mandelbrot iteration function are patched directly to
jsr to the XE versions, saving like 15 cycles per iter

Ok so it's not a lot, but every seconds counts. ;)

with XE code disabled:
1539 us/iter
5m13s

with old XE code:
1417 us/iter
4m48s

with new XE code:
1406 us/iter
4m45s
---
 mandel.s | 147 +++++++++++++++++++++++++++++++------------------------
 1 file changed, 82 insertions(+), 65 deletions(-)

diff --git a/mandel.s b/mandel.s
index 5edcbce..b0f9c28 100644
--- a/mandel.s
+++ b/mandel.s
@@ -485,6 +485,7 @@ input_max:
 .endmacro
 
 ; 6 * bytes cycles
+; 4 * bytes bytes
 .macro copy bytes, dest, arg
     .repeat bytes, byte ; 6 * bytes cycles
         lda arg + byte  ; 3 cyc
@@ -493,6 +494,7 @@ input_max:
 .endmacro
 
 ; 12 cycles
+; 8 bytes
 .macro copy16 dest, arg
     copy 2, dest, arg
 .endmacro
@@ -538,6 +540,8 @@ input_max:
 
 ; input: arg1, arg2 as fixed4.12
 ; output: dest as fixed8.24
+; patch point jsr at 16 bytes in
+imul16_patch_offset = 16
 .macro imul16 dest, arg1, arg2
     copy16 FR0, arg1  ; 12 cyc
     copy16 FR1, arg2  ; 12 cyc
@@ -547,6 +551,8 @@ input_max:
 
 ; input: arg as fixed4.12
 ; output: dest as fixed8.24
+; patch point jsr at 8 bytes in
+sqr16_patch_offset = 8
 .macro sqr16 dest, arg
     copy16 FR0, arg   ; 12 cyc
     jsr sqr16_func    ; ? cyc
@@ -692,71 +698,6 @@ bank_switch_table:
     .endif
 .endmacro
 
-.proc imul8xe_init
-
-    bank_switch 0
-    lda #0
-    sta EXTENDED_RAM
-    bank_switch 1
-    lda #1
-    sta EXTENDED_RAM
-    bank_switch 0
-    lda EXTENDED_RAM
-    beq init
-
-    ; no bank switching available, we just overwrite the value in base ram
-    rts
-
-init:
-
-    ; patch imul16_func into a forwarding thunk to imul16xe_func
-    lda #$4c ; 'jmp' opcode
-    sta imul16_func
-    lda #.lobyte(imul16xe_func)
-    sta imul16_func + 1
-    lda #.hibyte(imul16xe_func)
-    sta imul16_func + 2
-
-    ; ditto for sqr16_func -> sqr16xe_func
-    lda #$4c ; 'jmp' opcode
-    sta sqr16_func
-    lda #.lobyte(sqr16xe_func)
-    sta sqr16_func + 1
-    lda #.hibyte(sqr16xe_func)
-    sta sqr16_func + 2
-
-    ; create the lookup table
-    ; go through the input set, in four 16KB chunks
-
-    arg1 = FR1
-    arg2 = FR2
-    result = FR0
-
-    lda #$00
-    sta arg1
-    sta arg2
-    sta ptr
-    lda #$40
-    sta ptr + 1
-
-    ; $00 * $00 -> $3f * $ff
-    bank_switch 0
-    jsr imul8xe_init_section
-
-    ; $40 * $00 -> $7f * $ff
-    bank_switch 1
-    jsr imul8xe_init_section
-
-    ; $80 * $00 -> $bf * $ff
-    bank_switch 2
-    jsr imul8xe_init_section
-
-    ; $c0 * $00 -> $ff * $ff
-    bank_switch 3
-    jsr imul8xe_init_section
-
-    rts
-.endproc
 
 ; Initialize a 16 KB chunk of the table
 ; input: multipliers in temp
@@ -1156,12 +1097,15 @@ keep_going:
     shift_round_16 zy, 3
 
     ; zx_2 = zx * zx
+fixup_sqr16_1:
     sqr16 zx_2, zx + 2
 
     ; zy_2 = zy * zy
+fixup_sqr16_2:
     sqr16 zy_2, zy + 2
 
     ; zx_zy = zx * zy
+fixup_imul16_1:
     imul16 zx_zy, zx + 2, zy + 2
 
     ; dist = zx_2 + zy_2
@@ -2162,3 +2106,76 @@ countdown_done:
     jsr draw_string
     rts
 .endproc
+
+.proc imul8xe_init
+
+    bank_switch 0
+    lda #0
+    sta EXTENDED_RAM
+    bank_switch 1
+    lda #1
+    sta EXTENDED_RAM
+    bank_switch 0
+    lda EXTENDED_RAM
+    beq init
+
+    ; no bank switching available, we just overwrite the value in base ram
+    rts
+
+init:
+
+    ; patch imul16_func into a forwarding thunk to imul16xe_func
+    lda #$4c ; 'jmp' opcode
+    sta imul16_func
+    lda #.lobyte(imul16xe_func)
+    sta imul16_func + 1
+    sta mandelbrot::fixup_imul16_1 + imul16_patch_offset + 1
+    lda #.hibyte(imul16xe_func)
+    sta imul16_func + 2
+    sta mandelbrot::fixup_imul16_1 + imul16_patch_offset + 2
+
+    ; ditto for sqr16_func -> sqr16xe_func
+    lda #$4c ; 'jmp' opcode
+    sta sqr16_func
+    lda #.lobyte(sqr16xe_func)
+    sta sqr16_func + 1
+    sta mandelbrot::fixup_sqr16_1 + sqr16_patch_offset + 1
+    sta mandelbrot::fixup_sqr16_2 + sqr16_patch_offset + 1
+    lda #.hibyte(sqr16xe_func)
+    sta sqr16_func + 2
+    sta mandelbrot::fixup_sqr16_1 + sqr16_patch_offset + 2
+    sta mandelbrot::fixup_sqr16_2 + sqr16_patch_offset + 2
+
+
+    ; create the lookup table
+    ; go through the input set, in four 16KB chunks
+
+    arg1 = FR1
+    arg2 = FR2
+    result = FR0
+
+    lda #$00
+    sta arg1
+    sta arg2
+    sta ptr
+    lda #$40
+    sta ptr + 1
+
+    ; $00 * $00 -> $3f * $ff
+    bank_switch 0
+    jsr imul8xe_init_section
+
+    ; $40 * $00 -> $7f * $ff
+    bank_switch 1
+    jsr imul8xe_init_section
+
+    ; $80 * $00 -> $bf * $ff
+    bank_switch 2
+    jsr imul8xe_init_section
+
+    ; $c0 * $00 -> $ff * $ff
+    bank_switch 3
+    jsr imul8xe_init_section
+
+    rts
+.endproc

From 6479cf530c1c584f33b96f2b19885d02415863bb Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Tue, 16 Sep 2025 21:29:40 -0700
Subject: [PATCH 08/27] update some timings

---
 mandel.s | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/mandel.s b/mandel.s
index b0f9c28..b52f24a 100644
--- a/mandel.s
+++ b/mandel.s
@@ -461,7 +461,7 @@ input_max:
     sub 4, dest, arg1, arg2
 .endmacro
 
-; 3 + 5 * bytes cycles
+; 3 + 5 * (bytes - 1) cycles
 .macro shl bytes, arg
     asl arg              ; 3 cyc
     .repeat bytes-1, i
@@ -469,17 +469,17 @@ input_max:
     .endrepeat
 .endmacro
 
-; 13 cycles
+; 8 cycles
 .macro shl16 arg
     shl 2, arg
 .endmacro
 
-; 18 cycles
+; 13 cycles
 .macro shl24 arg
     shl 3, arg
 .endmacro
 
-; 23 cycles
+; 18 cycles
 .macro shl32 arg
     shl 4, arg
 .endmacro
@@ -529,11 +529,11 @@ input_max:
     neg 4, arg
 .endmacro
 
-; 11-27 + 23 * shift cycles
-; 103-119 cycles for shift=4
+; 11-27 + 18 * shift cycles
+; 65-81 cycles for shift=3
 .macro shift_round_16 arg, shift
     .repeat shift
-        shl32 arg ; 23 cycles
+        shl32 arg ; 18 cycles
     .endrepeat
     round16 arg ; 11-27 cycles
 .endmacro

From b27be3c1592c26609a26b6d0f82dcaf88aad5763 Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Sun, 28 Dec 2025 09:23:38 -0800
Subject: [PATCH 09/27] Add a C shell, which currently just passes through

This is a first step toward moving the UI to C and
adding file and network I/O in C. The fractal core
will remain in assembler as well as the multiplier.
---
 Makefile                  | 10 ++++---
 atari-xex.cfg             | 62 +++++++++++++++++++++++++++++++++++++++
 mandel.s => mandel-core.s |  4 +--
 mandel.c                  | 15 ++++++++++
 mandel.h                  |  4 +++
 5 files changed, 89 insertions(+), 6 deletions(-)
 create mode 100644 atari-xex.cfg
 rename mandel.s => mandel-core.s (99%)
 create mode 100644 mandel.c
 create mode 100644 mandel.h

diff --git a/Makefile b/Makefile
index 711adcd..c94074b 100644
--- a/Makefile
+++ b/Makefile
@@ -2,8 +2,11 @@
 
 all : mandel.xex
 
-mandel.xex : mandel.o tables.o atari-asm-xex.cfg
-	ld65 -C ./atari-asm-xex.cfg --mapfile mandel.map -o $@ mandel.o tables.o
+mandel.xex : mandel.o mandel-core.o tables.o atari-xex.cfg
+	ld65 -C ./atari-xex.cfg --mapfile mandel.map -o $@ mandel.o mandel-core.o tables.o atari.lib
+
+mandel.s : mandel.c mandel.h
+	cc65 -o $@ mandel.c
 
 %.o : %.s
 	ca65 -o $@ $<
@@ -13,8 +16,7 @@ tables.s : tables.js
 
 clean :
 	rm -f tables.s
+	rm -f mandel.s
 	rm -f *.o
 	rm -f *.xex
 	rm -f mandel.map
-
-
diff --git a/atari-xex.cfg b/atari-xex.cfg
new file mode 100644
index 0000000..ee41c4c
--- /dev/null
+++ b/atari-xex.cfg
@@ -0,0 +1,62 @@
+# Sample linker configuration for C programs using the Atari binary file support.
+# Use with: cl65 -tatari -Catari-xex.cfg prog.c -o prog.xex
+FEATURES {
+    STARTADDRESS: default = $2000;
+}
+SYMBOLS {
+    __SYSTEM_CHECK__:    type = import;  # force inclusion of "system check" load chunk
+    __STACKSIZE__:       type = weak, value = $0800; # 2k stack
+    __STARTADDRESS__:    type = export, value = %S;
+    __RESERVED_MEMORY__: type = weak, value = $0000;
+    __SYSCHKHDR__:       type = export, value = 0; # Disable system check header
+    __SYSCHKTRL__:       type = export, value = 0; # Disable system check trailer
+}
+MEMORY {
+    ZP:         file = "", define = yes, start = $0082, size = $007E;
+# "system check" load chunk
+    SYSCHKCHNK: file = %O,               start = $2E00, size = $0300;
+# "main program" load chunk
+# Note we reserve $4000-7fff for the bank-switch window.
+    #MAIN:       file = %O, define = yes, start = %S,    size = $BC20 - __STACKSIZE__ - __RESERVED_MEMORY__ - %S;
+    MAIN:       file = %O, define = yes, start = %S,    size = $4000 - __STACKSIZE__ - __RESERVED_MEMORY__ - %S;
+
+# Note $a000-$bfff is against the BASIC cartridge, may require booting with OPTION.
+    TABLES:  file = %O, define = yes, start = $8000, size = $a000 - $8000;
+}
+FILES {
+    %O: format = atari;
+}
+FORMATS {
+    atari: runad = start,
+           initad = SYSCHKCHNK: __SYSTEM_CHECK__;
+}
+SEGMENTS {
+    ZEROPAGE:  load = ZP,         type = zp;
+    EXTZP:     load = ZP,         type = zp,                optional = yes;
+    SYSCHK:    load = SYSCHKCHNK, type = rw,  define = yes, optional = yes;
+    STARTUP:   load = MAIN,       type = ro,  define = yes;
+    LOWBSS:    load = MAIN,       type = rw,                optional = yes;  # not zero initialized
+    LOWCODE:   load = MAIN,       type = ro,  define = yes, optional = yes;
+    ONCE:      load = MAIN,       type = ro,                optional = yes;
+    CODE:      load = MAIN,       type = ro,  define = yes;
+    RODATA:    load = MAIN,       type = ro;
+    DATA:      load = MAIN,       type = rw;
+    INIT:      load = MAIN,       type = rw,                optional = yes;
+    BSS:       load = MAIN,       type = bss, define = yes;
+    TABLES:    load = TABLES,     type = ro,  optional = yes, align = 256;
+}
+FEATURES {
+    CONDES: type    = constructor,
+            label   = __CONSTRUCTOR_TABLE__,
+            count   = __CONSTRUCTOR_COUNT__,
+            segment = ONCE;
+    CONDES: type    = destructor,
+            label   = __DESTRUCTOR_TABLE__,
+            count   = __DESTRUCTOR_COUNT__,
+            segment = RODATA;
+    CONDES: type    = interruptor,
+            label   = __INTERRUPTOR_TABLE__,
+            count   = __INTERRUPTOR_COUNT__,
+            segment = RODATA,
+            import  = __CALLIRQ__;
+}
diff --git a/mandel.s b/mandel-core.s
similarity index 99%
rename from mandel.s
rename to mandel-core.s
index b52f24a..6ebb089 100644
--- a/mandel.s
+++ b/mandel-core.s
@@ -361,7 +361,7 @@ z_buffer:
         .word 0
     .endrepeat
 
-.export start
+.export _mandel_start
 
 ;max_fill_level = 6
 max_fill_level = 3
@@ -1745,7 +1745,7 @@ zero_byte_loop:
     rts
 .endproc
 
-.proc start
+.proc _mandel_start
 
     jsr imul8xe_init
 
diff --git a/mandel.c b/mandel.c
new file mode 100644
index 0000000..f287fa3
--- /dev/null
+++ b/mandel.c
@@ -0,0 +1,15 @@
+/**
+ * The UI and I/O wrapper for the Mandelbrot runner, in C.
+ *
+ * For the moment *all* logic is in mandel-core.s, I'm just
+ * trying to get this to run within a cc65 environment.
+ * Eventually just the inner loop fun will live in there.
+ */
+
+#include <stdlib.h>
+#include <stdio.h>
+#include "mandel.h"
+
+void main(void) {
+    mandel_start();
+}
\ No newline at end of file
diff --git a/mandel.h b/mandel.h
new file mode 100644
index 0000000..e43fad7
--- /dev/null
+++ b/mandel.h
@@ -0,0 +1,4 @@
+#include <inttypes.h>
+
+// From mandel-core.s:
+extern void mandel_start(void);

From 97fdc12565c9f2e6b853b0e97688179195ee5281 Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Sun, 28 Dec 2025 12:32:57 -0800
Subject: [PATCH 10/27] Put the tables before the main code, and shrink the
 segment

Leaves more room for code and dynamic data/stack
---
 atari-xex.cfg | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/atari-xex.cfg b/atari-xex.cfg
index ee41c4c..e9090b4 100644
--- a/atari-xex.cfg
+++ b/atari-xex.cfg
@@ -10,18 +10,19 @@ SYMBOLS {
     __RESERVED_MEMORY__: type = weak, value = $0000;
     __SYSCHKHDR__:       type = export, value = 0; # Disable system check header
     __SYSCHKTRL__:       type = export, value = 0; # Disable system check trailer
+    __TABLESEG_SIZE__:     type = weak, value = 6 * $100;
+    __FRAMEBUFFER_START__: type = weak, value = $a000;
 }
 MEMORY {
     ZP:         file = "", define = yes, start = $0082, size = $007E;
 # "system check" load chunk
     SYSCHKCHNK: file = %O,               start = $2E00, size = $0300;
-# "main program" load chunk
 # Note we reserve $4000-7fff for the bank-switch window.
-    #MAIN:       file = %O, define = yes, start = %S,    size = $BC20 - __STACKSIZE__ - __RESERVED_MEMORY__ - %S;
-    MAIN:       file = %O, define = yes, start = %S,    size = $4000 - __STACKSIZE__ - __RESERVED_MEMORY__ - %S;
-
 # Note $a000-$bfff is against the BASIC cartridge, may require booting with OPTION.
-    TABLES:  file = %O, define = yes, start = $8000, size = $a000 - $8000;
+    TABLES:     file = %O, define = yes, start = %S, size = __TABLESEG_SIZE__;
+# "main program" load chunk
+    MAIN:       file = %O, define = yes, start = %S + __TABLESEG_SIZE__, size = __FRAMEBUFFER_START__ - __STACKSIZE__ - __RESERVED_MEMORY__ - __TABLESEG_SIZE__ - %S;
+
 }
 FILES {
     %O: format = atari;
@@ -34,6 +35,7 @@ SEGMENTS {
     ZEROPAGE:  load = ZP,         type = zp;
     EXTZP:     load = ZP,         type = zp,                optional = yes;
     SYSCHK:    load = SYSCHKCHNK, type = rw,  define = yes, optional = yes;
+    TABLES:    load = TABLES,     type = ro,  optional = yes, align = 256;
     STARTUP:   load = MAIN,       type = ro,  define = yes;
     LOWBSS:    load = MAIN,       type = rw,                optional = yes;  # not zero initialized
     LOWCODE:   load = MAIN,       type = ro,  define = yes, optional = yes;
@@ -43,7 +45,6 @@ SEGMENTS {
     DATA:      load = MAIN,       type = rw;
     INIT:      load = MAIN,       type = rw,                optional = yes;
     BSS:       load = MAIN,       type = bss, define = yes;
-    TABLES:    load = TABLES,     type = ro,  optional = yes, align = 256;
 }
 FEATURES {
     CONDES: type    = constructor,

From a93dd00e3697f9af47bb09a118722678b597a4cf Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Sun, 28 Dec 2025 12:55:08 -0800
Subject: [PATCH 11/27] Rearrange the segments a bit

* put TABLES in the low memory, before the bank switch window
* reserve bank switch window
* put rest of the code after that and before the framebuffer

so TABLES lives just before $4000
and MAIN lives in $8000-$bfff

could split some more code and/or data into low mem

and/or move the tables not used in extended memory mode into
the bank switch window so they take no address space on XE
or expanded memory machines
---
 atari-xex.cfg | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/atari-xex.cfg b/atari-xex.cfg
index e9090b4..467d9d4 100644
--- a/atari-xex.cfg
+++ b/atari-xex.cfg
@@ -1,7 +1,7 @@
 # Sample linker configuration for C programs using the Atari binary file support.
 # Use with: cl65 -tatari -Catari-xex.cfg prog.c -o prog.xex
 FEATURES {
-    STARTADDRESS: default = $2000;
+    STARTADDRESS: default = $8000;
 }
 SYMBOLS {
     __SYSTEM_CHECK__:    type = import;  # force inclusion of "system check" load chunk
@@ -10,19 +10,24 @@ SYMBOLS {
     __RESERVED_MEMORY__: type = weak, value = $0000;
     __SYSCHKHDR__:       type = export, value = 0; # Disable system check header
     __SYSCHKTRL__:       type = export, value = 0; # Disable system check trailer
+    __TABLESEG_START__:    type = weak, value = $2E00 + $0300;
     __TABLESEG_SIZE__:     type = weak, value = 6 * $100;
-    __FRAMEBUFFER_START__: type = weak, value = $a000;
+    __BANKSY_START__:  type = weak, value = $4000;
+    __BANKSY_SIZE__:   type = weak, value = $4000;
+    __FRAMEBUFFER_START__: type = weak, value = $A000;
 }
 MEMORY {
+# Note -- $80 and $81 (LOMEM) appear to be reserved in ZP.
     ZP:         file = "", define = yes, start = $0082, size = $007E;
 # "system check" load chunk
     SYSCHKCHNK: file = %O,               start = $2E00, size = $0300;
-# Note we reserve $4000-7fff for the bank-switch window.
 # Note $a000-$bfff is against the BASIC cartridge, may require booting with OPTION.
-    TABLES:     file = %O, define = yes, start = %S, size = __TABLESEG_SIZE__;
+    TABLES:     file = %O, define = yes, start = __TABLESEG_START__, size = __TABLESEG_SIZE__;
+# We reserve $4000-7fff for the bank-switch window.
+# In theory we could keep data and code here that we only use on 48k/64k systems.
+    BANKSWITCH: file = "", define = yes, start = __BANKSY_START__, size = __BANKSY_SIZE__;
 # "main program" load chunk
-    MAIN:       file = %O, define = yes, start = %S + __TABLESEG_SIZE__, size = __FRAMEBUFFER_START__ - __STACKSIZE__ - __RESERVED_MEMORY__ - __TABLESEG_SIZE__ - %S;
-
+    MAIN:       file = %O, define = yes, start = %S, size = __FRAMEBUFFER_START__ - __STACKSIZE__ - __RESERVED_MEMORY__ - %S;
 }
 FILES {
     %O: format = atari;
@@ -36,6 +41,7 @@ SEGMENTS {
     EXTZP:     load = ZP,         type = zp,                optional = yes;
     SYSCHK:    load = SYSCHKCHNK, type = rw,  define = yes, optional = yes;
     TABLES:    load = TABLES,     type = ro,  optional = yes, align = 256;
+    BANKSWICH: load = BANKSWITCH, type = ro,  optional = yes;
     STARTUP:   load = MAIN,       type = ro,  define = yes;
     LOWBSS:    load = MAIN,       type = rw,                optional = yes;  # not zero initialized
     LOWCODE:   load = MAIN,       type = ro,  define = yes, optional = yes;

From 25c37a1188b8726f95cee5615fc94cbb34765b0c Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Wed, 8 Apr 2026 19:58:27 -0700
Subject: [PATCH 12/27] zeropage tweaks

* switched zero-page from hardcoded assignments to symbols
* moved most non-hotpath stuff out to .data
* merged ptr and pixel_ptr

Slight slowdown in Atari800MacX from 5m13s to 5m15s
---
 mandel-core.s | 103 +++++++++++++++++++++++++-------------------------
 1 file changed, 52 insertions(+), 51 deletions(-)

diff --git a/mandel-core.s b/mandel-core.s
index 6ebb089..34dff8b 100644
--- a/mandel-core.s
+++ b/mandel-core.s
@@ -1,44 +1,44 @@
-; Our zero-page vars
-ox              = $80 ; fixed6.26: center point x
-oy              = $84 ; fixed6.26: center point y
-cx              = $88 ; fixed6.26: c_x
-cy              = $8c ; fixed6.26: c_y
+.zeropage
 
-zx              = $90 ; fixed6.26: z_x
-zy              = $94 ; fixed6.26: z_y
-zx_2            = $98 ; fixed6.26: z_x^2
-zy_2            = $9c ; fixed6.26: z_y^2
+ox:              .res 4 ; fixed6.26: center point x
+oy:              .res 4 ; fixed6.26: center point y
+cx:              .res 4 ; fixed6.26: c_x
+cy:              .res 4 ; fixed6.26: c_y
 
-zx_zy           = $a0 ; fixed6.26: z_x * z_y
-dist            = $a4 ; fixed6.26: z_x^2 + z_y^2
-sx              = $a8 ; i16: screen pixel x
-sy              = $aa ; i16: screen pixel y
-z_buffer_active = $ac ; boolean: 1 if we triggered the lake, 0 if not
-z_buffer_start  = $ad ; u8: index into z_buffer
-z_buffer_end    = $ae ; u8: index into z_buffer
-iter            = $af ; u8: iteration count
+zx:              .res 4 ; fixed6.26: z_x
+zy:              .res 4 ; fixed6.26: z_y
+zx_2:            .res 4 ; fixed6.26: z_x^2
+zy_2:            .res 4 ; fixed6.26: z_y^2
 
-ptr             = $b0 ; u16
-pixel_ptr       = $b2 ; u16
-zoom            = $b4 ; u8: zoom shift level
-fill_level      = $b5 ; u8
-pixel_color     = $b6 ; u8
-pixel_mask      = $b7 ; u8
-pixel_shift     = $b8 ; u8
-pixel_offset    = $b9 ; u8
-palette_offset  = $ba ; u8
-chroma_offset   = $bb ; u8
-palette_ticks   = $bc ; u8
-chroma_ticks    = $bd ; u8
-count_frames    = $be ; u8
-; free space $bf
+zx_zy:           .res 4 ; fixed6.26: z_x * z_y
+dist:            .res 4 ; fixed6.26: z_x^2 + z_y^2
 
-count_iters     = $c0 ; u16
-text_col        = $c2 ; u8
-text_row        = $c3 ; u8
-; free space c4-cb
-temp            = $cc ; u16
-temp2           = $ce ; u16
+z_buffer_active: .res 1 ; boolean: 1 if we triggered the lake, 0 if not
+z_buffer_start:  .res 1 ; u8: index into z_buffer
+z_buffer_end:    .res 1 ; u8: index into z_buffer
+iter:            .res 1 ; u8: iteration count
+ptr:             .res 2 ; u16
+temp:            .res 2 ; u16
+temp2:           .res 2 ; u16
+
+.data
+; can move to .data
+sx:              .res 2 ; i16: screen pixel x
+sy:              .res 2 ; i16: screen pixel y
+zoom:            .res 1 ; u8: zoom shift level
+fill_level:      .res 1 ; u8
+pixel_color:     .res 1 ; u8
+pixel_mask:      .res 1 ; u8
+pixel_shift:     .res 1 ; u8
+pixel_offset:    .res 1 ; u8
+palette_offset:  .res 1 ; u8
+chroma_offset:   .res 1 ; u8
+palette_ticks:   .res 1 ; u8
+chroma_ticks:    .res 1 ; u8
+count_frames:    .res 1 ; u8
+count_iters:     .res 2 ; u16
+text_col:        .res 1 ; u8
+text_row:        .res 1 ; u8
 
 palette_delay = 23
 chroma_delay = 137
@@ -131,6 +131,8 @@ KEY_E     = 42
 KEY_X     = 22
 KEY_Y     = 43
 
+.data
+
 .struct float48
     exponent .byte
     mantissa .byte 5
@@ -142,7 +144,6 @@ KEY_Y     = 43
 .import sqr_lobyte
 .import sqr_hibyte
 
-.data
 
 strings:
 str_self:
@@ -1253,21 +1254,21 @@ enough:
 negative:
     ; temp1 = top half
     lda #.lobyte(framebuffer_top + stride * half_height)
-    sta pixel_ptr
+    sta ptr
     lda #.hibyte(framebuffer_top + stride * half_height)
-    sta pixel_ptr + 1
+    sta ptr + 1
     jmp point
 
 positive:
 
     lda #.lobyte(framebuffer_bottom)
-    sta pixel_ptr
+    sta ptr
     lda #.hibyte(framebuffer_bottom)
-    sta pixel_ptr + 1
+    sta ptr + 1
 
 point:
 
-    ; pixel_ptr += sy * stride
+    ; ptr += sy * stride
     ;    temp * 40
     ; =  temp * 32  +  temp * 8
     ; = (temp << 5) + (temp << 3)
@@ -1275,10 +1276,10 @@ point:
     shl16 temp
     shl16 temp
     shl16 temp
-    add16 pixel_ptr, pixel_ptr, temp
+    add16 ptr, ptr, temp
     shl16 temp
     shl16 temp
-    add16 pixel_ptr, pixel_ptr, temp
+    add16 ptr, ptr, temp
 
     ; Ok so temp1 points to the start of the line, which is 40 bytes.
     ; Get the byte and bit offsets
@@ -1318,20 +1319,20 @@ shift_done:
 
 draw_pixel:
     ; read, mask, or, write
-    lda (pixel_ptr),y
+    lda (ptr),y
     and pixel_mask
     ora pixel_color
-    sta (pixel_ptr),y
+    sta (ptr),y
 
     dex
     beq done
     clc
     lda #40
-    adc pixel_ptr
-    sta pixel_ptr
+    adc ptr
+    sta ptr
     lda #0
-    adc pixel_ptr + 1
-    sta pixel_ptr + 1
+    adc ptr + 1
+    sta ptr + 1
     jmp draw_pixel
 
 done:

From 3ce4c1e580bfa6d186aa89f4e2b199cff7b7e5d7 Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Sat, 22 Aug 2026 13:01:23 -0700
Subject: [PATCH 13/27] Add some timing notes

---
 mandel-core.s | 68 +++++++++++++++++++++++++++++----------------------
 1 file changed, 39 insertions(+), 29 deletions(-)

diff --git a/mandel-core.s b/mandel-core.s
index 34dff8b..5080d7e 100644
--- a/mandel-core.s
+++ b/mandel-core.s
@@ -563,12 +563,13 @@ sqr16_patch_offset = 8
 ; input: arg as u8
 ; output: dest as u16
 ; clobbers a, x
+; 19 cyc
 .macro sqr8 dest, arg
-    ldx arg
-    lda sqr_lobyte,x
-    sta dest
-    lda sqr_hibyte,x
-    sta dest + 1
+    ldx arg           ; 3 cyc
+    lda sqr_lobyte,x  ; 5 cyc
+    sta dest          ; 3 cyc
+    lda sqr_hibyte,x  ; 5 cyc
+    sta dest + 1      ; 3 cyc
 .endmacro
 
 .segment "TABLES"
@@ -770,6 +771,10 @@ inner_loop:
 
 .endproc
 
+; min low-mem: 81 * 4 + 28 * 2 + 10 + 6 = 396 cyc
+; max low-mem: 92 * 4 + 28 * 2 + 50 + 6 = 480 cyc
+; min ext-mem: 51 * 4 + 28 * 2 + 10 + 6 = 276 cyc
+; max low-mem: 70 * 4 + 28 * 2 + 50 + 6 = 392 cyc
 .macro imul16_impl xe
     .local arg1
     .local arg2
@@ -787,32 +792,37 @@ inner_loop:
     ; h1*256*(h2*256 + l2) + l1*(h2*256 + l2)
     ; h1*h2*256*256 + h1*l2*256 + h2*l1*256 + l1*l2
 
-    imul8 result, arg1, arg2, xe
+    imul8 result, arg1, arg2, xe        ; 81-92 or 51-70
 
-    imul8 result + 2, arg1 + 1, arg2 + 1, xe
+    imul8 result + 2, arg1 + 1, arg2 + 1, xe ; 81-92 or 51-70
 
-    imul8 inter, arg1 + 1, arg2, xe
-    add16 result + 1, result + 1, inter
-    add_carry result + 3
+    imul8 inter, arg1 + 1, arg2, xe     ; 81-92 or 51-70
+    add16 result + 1, result + 1, inter ; 20 cyc
+    add_carry result + 3                ; 8 cyc
 
-    imul8 inter, arg1, arg2 + 1, xe
-    add16 result + 1, result + 1, inter
-    add_carry result + 3
+    imul8 inter, arg1, arg2 + 1, xe     ; 81-92 or 51-70
+    add16 result + 1, result + 1, inter ; 20 cyc
+    add_carry result + 3                ; 8 cyc
 
     ; In case of negative inputs, adjust high word
     ; https://stackoverflow.com/a/28827013
-    lda arg1 + 1
-    bpl arg1_pos
-    sub16 result + 2, result + 2, arg2
+    ; 10-50 cycles
+    lda arg1 + 1                       ; 3 cyc
+    bpl arg1_pos                       ; 2 cyc
+    sub16 result + 2, result + 2, arg2 ; 20 cyc
 arg1_pos:
-    lda arg2 + 1
-    bpl arg2_pos
-    sub16 result + 2, result + 2, arg1
+    lda arg2 + 1                       ; 3 cyc
+    bpl arg2_pos                       ; 2 cyc
+    sub16 result + 2, result + 2, arg1 ; 20 cyc
 arg2_pos:
 
     rts ; 6 cyc
 .endmacro
 
+; min base ram: 19 * 2 + 81 + 28 * 2 + 6 = 181
+; max base ram: 19 * 2 + 92 + 28 * 2 + 6 = 192
+; min ext ram: 19 * 2 + 51 + 28 * 2 + 6 = 151
+; max ext ram: 19 * 2 + 70 + 28 * 2 + 6 = 170
 .macro sqr16_impl xe
     .scope
         arg = FR0    ; 16-bit arg (clobbered)
@@ -820,9 +830,9 @@ arg2_pos:
         ;inter = temp2
         inter = FR1
 
-        lda arg + 1
-        bpl arg_pos
-        neg16 arg
+        lda arg + 1  ; 3 cyc
+        bpl arg_pos  ; 2 cyc
+        neg16 arg    ; 18 cyc
     arg_pos:
 
         ; hl * hl
@@ -830,15 +840,15 @@ arg2_pos:
         ; h*256*(h*256 + l) + l*(h*256 + l)
         ; h*h*256*256 + h*l*256 + h*l*256 + l*l
 
-        sqr8 result, arg
+        sqr8 result, arg          ; 19 cyc
 
-        sqr8 result + 2, arg + 1
+        sqr8 result + 2, arg + 1  ; 19 cyc
 
-        imul8 inter, arg + 1, arg, xe
-        add16 result + 1, result + 1, inter
-        add_carry result + 3
-        add16 result + 1, result + 1, inter
-        add_carry result + 3
+        imul8 inter, arg + 1, arg, xe        ; 81-92 / 51-70 cyc
+        add16 result + 1, result + 1, inter  ; 20 cyc
+        add_carry result + 3                 ; 8 cyc
+        add16 result + 1, result + 1, inter  ; 20 cyc
+        add_carry result + 3                 ; 8 cyc
 
         rts ; 6 cyc
     .endscope

From 173901e49a24922700c8d54825d822d0f62fd2d3 Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Sat, 22 Aug 2026 13:01:56 -0700
Subject: [PATCH 14/27] Add a copy of the old bit-shift multiplier code

---
 bitmul.s | 124 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 124 insertions(+)
 create mode 100644 bitmul.s

diff --git a/bitmul.s b/bitmul.s
new file mode 100644
index 0000000..df84704
--- /dev/null
+++ b/bitmul.s
@@ -0,0 +1,124 @@
+; the old 16-bit bit-and-shift multiplier
+; copied from old code, won't compile as-is
+
+; inner loop for imul16
+; bitnum < 8: 25 or 41 cycles
+; bitnum >= 8: 30 or 46 cycles
+.macro bitmul16 arg1, arg2, result, bitnum
+    .local zero
+    .local one
+    .local next
+
+    ; does 16-bit adds
+    ; arg1 and arg2 are treated as unsigned
+    ; negative signed inputs must be flipped first
+
+    ; 7 cycles up to the branch
+
+    ; check if arg1 has 0 or 1 bit in this place
+    ; 5 cycles either way
+    .if bitnum < 8
+        lda arg1                 ; 3 cyc
+        and #(1 << (bitnum))       ; 2 cyc
+    .else
+        lda arg1 + 1             ; 3 cyc
+        and #(1 << ((bitnum) - 8)) ; 2 cyc
+    .endif
+    bne one ; 2 cyc
+
+zero: ; 18 cyc, 23 cyc
+    lsr result + 3 ; 5 cyc
+    jmp next       ; 3 cyc
+
+one: ; 32 cyc, 37 cyc
+    ; 16-bit add on the top bits
+    clc            ; 2 cyc
+    lda result + 2 ; 3 cyc
+    adc arg2       ; 3 cyc
+    sta result + 2 ; 3 cyc
+    lda result + 3 ; 3 cyc
+    adc arg2 + 1   ; 3 cyc
+    ror a          ; 2 cyc - get a jump on the shift
+    sta result + 3 ; 3 cyc
+next:
+    ror result + 2 ; 5 cyc
+    ror result + 1 ; 5 cyc
+    .if bitnum >= 8
+        ; we can save 5 cycles * 8 bits = 40 cycles total by skipping this byte
+        ; when it's all uninitialized data
+        ror result ; 5 cyc
+    .endif
+
+.endmacro
+
+; 5 to 25 cycles
+.macro check_sign arg
+    ; Check sign bit and flip argument to postive,
+    ; keeping a count of sign bits in the X register.
+    .local positive
+    lda arg + 1   ; 3 cyc
+    bpl positive  ; 2 cyc
+    neg16 arg     ; 18 cyc
+    inx           ; 2 cyc
+positive:
+.endmacro
+
+; 518 - 828 cyc
+.macro imul16 dest, arg1, arg2
+    copy16 FR0, arg1  ; 12 cyc
+    copy16 FR1, arg2  ; 12 cyc
+    jsr imul16_func   ; 470-780 cyc
+    copy32 dest, FR2  ; 24 cyc
+.endmacro
+
+
+.macro shift_round_16 arg, shift
+    .repeat shift
+        shl32 arg
+    .endrepeat
+    round16 arg
+.endmacro
+
+.macro imul16_round dest, arg1, arg2, shift
+    copy16 FR0, arg1  ; 12 cyc
+    copy16 FR1, arg2  ; 12 cyc
+    jsr imul16_func   ; 470-780 cyc
+    shift_round_16 FR2, shift
+    copy16 dest, FR2 + 2  ; 12 cyc
+.endmacro
+
+; min 470 cycles
+; max 780 cycles
+.proc imul16_func
+    arg1 = FR0   ; 16-bit arg (clobbered)
+    arg2 = FR1   ; 16-bit arg (clobbered)
+    result = FR2 ; 32-bit result
+
+    ldx #0          ; 2 cyc
+    ; counts the number of sign bits in X
+    check_sign arg1 ; 5 to 25 cyc
+    check_sign arg2 ; 5 to 25 cyc
+    
+    ; zero out the 32-bit temp's top 16 bits
+    lda #0          ; 2 cyc
+    sta result + 2  ; 3 cyc
+    sta result + 3  ; 3 cyc
+    ; the bottom two bytes will get cleared by the shifts
+
+    ; unrolled loop for maximum speed, at the cost
+    ; of a larger routine
+    ; 440 to 696 cycles
+    .repeat 16, bitnum
+        ; bitnum < 8: 25 or 41 cycles
+        ; bitnum >= 8: 30 or 46 cycles
+        bitmul16 arg1, arg2, result, bitnum
+    .endrepeat
+
+    ; In case of mixed input signs, return a negative result.
+    cpx #1              ; 2 cyc
+    bne positive_result ; 2 cyc
+    neg32 result        ; 34 cyc
+positive_result:
+
+    rts ; 6 cyc
+.endproc

From d9f7ce3e356102f62af03f51f73eeea73c762562 Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Sat, 22 Aug 2026 14:27:52 -0700
Subject: [PATCH 15/27] whoops missed a bit

---
 mandel-core.s | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/mandel-core.s b/mandel-core.s
index 5080d7e..eefd557 100644
--- a/mandel-core.s
+++ b/mandel-core.s
@@ -819,10 +819,10 @@ arg2_pos:
     rts ; 6 cyc
 .endmacro
 
-; min base ram: 19 * 2 + 81 + 28 * 2 + 6 = 181
-; max base ram: 19 * 2 + 92 + 28 * 2 + 6 = 192
-; min ext ram: 19 * 2 + 51 + 28 * 2 + 6 = 151
-; max ext ram: 19 * 2 + 70 + 28 * 2 + 6 = 170
+; min base ram: 5 + 19 * 2 + 81 + 28 * 2 + 6 = 186
+; max base ram: 23 + 19 * 2 + 92 + 28 * 2 + 6 = 215
+; min ext ram: 5 + 19 * 2 + 51 + 28 * 2 + 6 = 156
+; max ext ram: 23 + 19 * 2 + 70 + 28 * 2 + 6 = 193
 .macro sqr16_impl xe
     .scope
         arg = FR0    ; 16-bit arg (clobbered)
@@ -830,6 +830,7 @@ arg2_pos:
         ;inter = temp2
         inter = FR1
 
+        ; 5-23 cycles
         lda arg + 1  ; 3 cyc
         bpl arg_pos  ; 2 cyc
         neg16 arg    ; 18 cyc

From b4cb773cf1fb128246a461c869f277e9ea5fa806 Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Sat, 22 Aug 2026 14:34:53 -0700
Subject: [PATCH 16/27] tweak comment

---
 mandel-core.s | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mandel-core.s b/mandel-core.s
index eefd557..5e56e87 100644
--- a/mandel-core.s
+++ b/mandel-core.s
@@ -771,10 +771,10 @@ inner_loop:
 
 .endproc
 
-; min low-mem: 81 * 4 + 28 * 2 + 10 + 6 = 396 cyc
-; max low-mem: 92 * 4 + 28 * 2 + 50 + 6 = 480 cyc
+; min base mem: 81 * 4 + 28 * 2 + 10 + 6 = 396 cyc
+; max base mem: 92 * 4 + 28 * 2 + 50 + 6 = 480 cyc
 ; min ext-mem: 51 * 4 + 28 * 2 + 10 + 6 = 276 cyc
-; max low-mem: 70 * 4 + 28 * 2 + 50 + 6 = 392 cyc
+; max ext-mem: 70 * 4 + 28 * 2 + 50 + 6 = 392 cyc
 .macro imul16_impl xe
     .local arg1
     .local arg2

From 829f46755ad73438828440a23ed082e46e7a6d8d Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Sat, 22 Aug 2026 14:43:17 -0700
Subject: [PATCH 17/27] Save another few cycles per multiple

add_carry took a fixed 8 cycles with a lda/adc/sta pattern

we can instead use bcc to handle the carry-not-set case in just
2 cycles, skipping over the inc which takes 5 cycles on the
carry-is-set case.

Result is 2-7 cycles instead of 8, saving 1-6 cycles twice
per 16-bit multiplication or square.

Neat!
---
 mandel-core.s | 34 ++++++++++++++++++----------------
 1 file changed, 18 insertions(+), 16 deletions(-)

diff --git a/mandel-core.s b/mandel-core.s
index 5e56e87..a153ff5 100644
--- a/mandel-core.s
+++ b/mandel-core.s
@@ -435,11 +435,13 @@ input_max:
     add 4, dest, arg1, arg2
 .endmacro
 
-; 8 cycles
+; 2-7 cycles
 .macro add_carry dest
-    lda dest ; 3 cyc
-    adc #0   ; 2 cyc
-    sta dest ; 3 cyc
+    .scope
+        bcc after ; 2 cyc
+        inc dest  ; 5 cyc
+    after:
+    .endscope
 .endmacro
 
 ; 2 + 9 * byte cycles
@@ -771,10 +773,10 @@ inner_loop:
 
 .endproc
 
-; min base mem: 81 * 4 + 28 * 2 + 10 + 6 = 396 cyc
-; max base mem: 92 * 4 + 28 * 2 + 50 + 6 = 480 cyc
-; min ext-mem: 51 * 4 + 28 * 2 + 10 + 6 = 276 cyc
-; max ext-mem: 70 * 4 + 28 * 2 + 50 + 6 = 392 cyc
+; min base mem: 81 * 4 + 22 * 2 + 10 + 6 = 384 cyc
+; max base mem: 92 * 4 + 27 * 2 + 50 + 6 = 478 cyc
+; min ext-mem: 51 * 4 + 22 * 2 + 10 + 6 = 264 cyc
+; max ext-mem: 70 * 4 + 27 * 2 + 50 + 6 = 390 cyc
 .macro imul16_impl xe
     .local arg1
     .local arg2
@@ -798,11 +800,11 @@ inner_loop:
 
     imul8 inter, arg1 + 1, arg2, xe     ; 81-92 or 51-70
     add16 result + 1, result + 1, inter ; 20 cyc
-    add_carry result + 3                ; 8 cyc
+    add_carry result + 3                ; 2-7 cyc
 
     imul8 inter, arg1, arg2 + 1, xe     ; 81-92 or 51-70
     add16 result + 1, result + 1, inter ; 20 cyc
-    add_carry result + 3                ; 8 cyc
+    add_carry result + 3                ; 2-7 cyc
 
     ; In case of negative inputs, adjust high word
     ; https://stackoverflow.com/a/28827013
@@ -819,10 +821,10 @@ arg2_pos:
     rts ; 6 cyc
 .endmacro
 
-; min base ram: 5 + 19 * 2 + 81 + 28 * 2 + 6 = 186
-; max base ram: 23 + 19 * 2 + 92 + 28 * 2 + 6 = 215
-; min ext ram: 5 + 19 * 2 + 51 + 28 * 2 + 6 = 156
-; max ext ram: 23 + 19 * 2 + 70 + 28 * 2 + 6 = 193
+; min base ram: 5 + 19 * 2 + 81 + 22 * 2 + 6 = 174
+; max base ram: 23 + 19 * 2 + 92 + 27 * 2 + 6 = 213
+; min ext ram: 5 + 19 * 2 + 51 + 22 * 2 + 6 = 144
+; max ext ram: 23 + 19 * 2 + 70 + 27 * 2 + 6 = 191
 .macro sqr16_impl xe
     .scope
         arg = FR0    ; 16-bit arg (clobbered)
@@ -847,9 +849,9 @@ arg2_pos:
 
         imul8 inter, arg + 1, arg, xe        ; 81-92 / 51-70 cyc
         add16 result + 1, result + 1, inter  ; 20 cyc
-        add_carry result + 3                 ; 8 cyc
+        add_carry result + 3                 ; 2-7 cyc
         add16 result + 1, result + 1, inter  ; 20 cyc
-        add_carry result + 3                 ; 8 cyc
+        add_carry result + 3                 ; 2-7 cyc
 
         rts ; 6 cyc
     .endscope

From 27995007c5da6b259069bf7147d0ce19c25125a9 Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Sat, 22 Aug 2026 15:25:58 -0700
Subject: [PATCH 18/27] experiment

---
 mandel-core.s | 24 +++++++++++-------------
 1 file changed, 11 insertions(+), 13 deletions(-)

diff --git a/mandel-core.s b/mandel-core.s
index a153ff5..69980b8 100644
--- a/mandel-core.s
+++ b/mandel-core.s
@@ -592,7 +592,7 @@ bank_switch_table:
 .macro imul8 dest, arg1, arg2, xe
     .if xe
         ; using 64KB lookup table
-        ; 51-70 cycles
+        ; 52-69 cycles
         ; clobbers x, y, dest, ptr
         .scope
             output = dest
@@ -636,9 +636,7 @@ bank_switch_table:
             txa          ; 2 cyc
             adc output   ; 3 cyc
             sta output   ; 3 cyc
-            lda #0       ; 2 cyc
-            adc output+1 ; 3 cyc
-            sta output+1 ; 3 cyc
+            add_carry output + 1 ; 2-7 cyc
 
         done:
         .endscope
@@ -775,8 +773,8 @@ inner_loop:
 
 ; min base mem: 81 * 4 + 22 * 2 + 10 + 6 = 384 cyc
 ; max base mem: 92 * 4 + 27 * 2 + 50 + 6 = 478 cyc
-; min ext-mem: 51 * 4 + 22 * 2 + 10 + 6 = 264 cyc
-; max ext-mem: 70 * 4 + 27 * 2 + 50 + 6 = 390 cyc
+; min ext-mem: 52 * 4 + 22 * 2 + 10 + 6 = 268 cyc
+; max ext-mem: 69 * 4 + 27 * 2 + 50 + 6 = 386 cyc
 .macro imul16_impl xe
     .local arg1
     .local arg2
@@ -794,15 +792,15 @@ inner_loop:
     ; h1*256*(h2*256 + l2) + l1*(h2*256 + l2)
     ; h1*h2*256*256 + h1*l2*256 + h2*l1*256 + l1*l2
 
-    imul8 result, arg1, arg2, xe        ; 81-92 or 51-70
+    imul8 result, arg1, arg2, xe        ; 81-92 or 52-69
 
-    imul8 result + 2, arg1 + 1, arg2 + 1, xe ; 81-92 or 51-70
+    imul8 result + 2, arg1 + 1, arg2 + 1, xe ; 81-92 or 52-69
 
-    imul8 inter, arg1 + 1, arg2, xe     ; 81-92 or 51-70
+    imul8 inter, arg1 + 1, arg2, xe     ; 81-92 or 52-69
     add16 result + 1, result + 1, inter ; 20 cyc
     add_carry result + 3                ; 2-7 cyc
 
-    imul8 inter, arg1, arg2 + 1, xe     ; 81-92 or 51-70
+    imul8 inter, arg1, arg2 + 1, xe     ; 81-92 or 52-69
     add16 result + 1, result + 1, inter ; 20 cyc
     add_carry result + 3                ; 2-7 cyc
 
@@ -823,8 +821,8 @@ arg2_pos:
 
 ; min base ram: 5 + 19 * 2 + 81 + 22 * 2 + 6 = 174
 ; max base ram: 23 + 19 * 2 + 92 + 27 * 2 + 6 = 213
-; min ext ram: 5 + 19 * 2 + 51 + 22 * 2 + 6 = 144
-; max ext ram: 23 + 19 * 2 + 70 + 27 * 2 + 6 = 191
+; min ext ram: 5 + 19 * 2 + 52 + 22 * 2 + 6 = 145
+; max ext ram: 23 + 19 * 2 + 69 + 27 * 2 + 6 = 190
 .macro sqr16_impl xe
     .scope
         arg = FR0    ; 16-bit arg (clobbered)
@@ -847,7 +845,7 @@ arg2_pos:
 
         sqr8 result + 2, arg + 1  ; 19 cyc
 
-        imul8 inter, arg + 1, arg, xe        ; 81-92 / 51-70 cyc
+        imul8 inter, arg + 1, arg, xe        ; 81-92 / 52-69 cyc
         add16 result + 1, result + 1, inter  ; 20 cyc
         add_carry result + 3                 ; 2-7 cyc
         add16 result + 1, result + 1, inter  ; 20 cyc

From e284587edc743cce7961c61c0c0ccacce9ce9edd Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Sat, 22 Aug 2026 15:35:03 -0700
Subject: [PATCH 19/27] Fix regression from merging ptr and pixel_ptr

the XE fast-path assumed low byte of ptr never changes
to save a couple cycles
---
 mandel-core.s | 27 ++++++++++++++-------------
 1 file changed, 14 insertions(+), 13 deletions(-)

diff --git a/mandel-core.s b/mandel-core.s
index 34dff8b..348e072 100644
--- a/mandel-core.s
+++ b/mandel-core.s
@@ -18,6 +18,7 @@ z_buffer_start:  .res 1 ; u8: index into z_buffer
 z_buffer_end:    .res 1 ; u8: index into z_buffer
 iter:            .res 1 ; u8: iteration count
 ptr:             .res 2 ; u16
+pixel_ptr:       .res 2 ; u16
 temp:            .res 2 ; u16
 temp2:           .res 2 ; u16
 
@@ -1254,21 +1255,21 @@ enough:
 negative:
     ; temp1 = top half
     lda #.lobyte(framebuffer_top + stride * half_height)
-    sta ptr
+    sta pixel_ptr
     lda #.hibyte(framebuffer_top + stride * half_height)
-    sta ptr + 1
+    sta pixel_ptr + 1
     jmp point
 
 positive:
 
     lda #.lobyte(framebuffer_bottom)
-    sta ptr
+    sta pixel_ptr
     lda #.hibyte(framebuffer_bottom)
-    sta ptr + 1
+    sta pixel_ptr + 1
 
 point:
 
-    ; ptr += sy * stride
+    ; pixel_ptr += sy * stride
     ;    temp * 40
     ; =  temp * 32  +  temp * 8
     ; = (temp << 5) + (temp << 3)
@@ -1276,10 +1277,10 @@ point:
     shl16 temp
     shl16 temp
     shl16 temp
-    add16 ptr, ptr, temp
+    add16 pixel_ptr, pixel_ptr, temp
     shl16 temp
     shl16 temp
-    add16 ptr, ptr, temp
+    add16 pixel_ptr, pixel_ptr, temp
 
     ; Ok so temp1 points to the start of the line, which is 40 bytes.
     ; Get the byte and bit offsets
@@ -1319,20 +1320,20 @@ shift_done:
 
 draw_pixel:
     ; read, mask, or, write
-    lda (ptr),y
+    lda (pixel_ptr),y
     and pixel_mask
     ora pixel_color
-    sta (ptr),y
+    sta (pixel_ptr),y
 
     dex
     beq done
     clc
     lda #40
-    adc ptr
-    sta ptr
+    adc pixel_ptr
+    sta pixel_ptr
     lda #0
-    adc ptr + 1
-    sta ptr + 1
+    adc pixel_ptr + 1
+    sta pixel_ptr + 1
     jmp draw_pixel
 
 done:

From f6489670b117f8c4a2463a81c62c7af4b135852e Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Sat, 22 Aug 2026 15:58:17 -0700
Subject: [PATCH 20/27] comments

---
 mandel-core.s | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/mandel-core.s b/mandel-core.s
index f021749..ddcd7fc 100644
--- a/mandel-core.s
+++ b/mandel-core.s
@@ -793,14 +793,18 @@ inner_loop:
     ; h1*256*(h2*256 + l2) + l1*(h2*256 + l2)
     ; h1*h2*256*256 + h1*l2*256 + h2*l1*256 + l1*l2
 
+    ; l1 * l2
     imul8 result, arg1, arg2, xe        ; 81-92 or 52-69
 
+    ; 256 * 256 * h1 * h2
     imul8 result + 2, arg1 + 1, arg2 + 1, xe ; 81-92 or 52-69
 
+    ; 256 * h1 * l1
     imul8 inter, arg1 + 1, arg2, xe     ; 81-92 or 52-69
     add16 result + 1, result + 1, inter ; 20 cyc
     add_carry result + 3                ; 2-7 cyc
 
+    ; 256 * l1 * h2
     imul8 inter, arg1, arg2 + 1, xe     ; 81-92 or 52-69
     add16 result + 1, result + 1, inter ; 20 cyc
     add_carry result + 3                ; 2-7 cyc
@@ -842,10 +846,13 @@ arg2_pos:
         ; h*256*(h*256 + l) + l*(h*256 + l)
         ; h*h*256*256 + h*l*256 + h*l*256 + l*l
 
+        ; l * l
         sqr8 result, arg          ; 19 cyc
 
+        ; 256 * 256 * hl * hl
         sqr8 result + 2, arg + 1  ; 19 cyc
 
+        ; 2 * h * l * 256
         imul8 inter, arg + 1, arg, xe        ; 81-92 / 52-69 cyc
         add16 result + 1, result + 1, inter  ; 20 cyc
         add_carry result + 3                 ; 2-7 cyc

From 23fa002f3393563da4195b6248a03632ee35872a Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Sat, 22 Aug 2026 16:30:41 -0700
Subject: [PATCH 21/27] comments

---
 mandel-core.s | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mandel-core.s b/mandel-core.s
index ddcd7fc..1f7234b 100644
--- a/mandel-core.s
+++ b/mandel-core.s
@@ -599,12 +599,14 @@ bank_switch_table:
             output = dest
 
             ; top 2 bits are the table bank selector
+            ; note we keep arg2 in X after this lookup as we need it later!
             ldx arg2                ; 3 cyc
             lda bank_switch_table,x ; 4 cyc
             sta PORTB               ; 4 cyc
 
             ; bottom 14 bits except the LSB are the per-bank table index
             ; add $4000 for the bank pointer
+            ; note the low byte of ptr is assumed to remain at 0! do not clobber it!
             txa          ; 2 cyc
             and #$3f     ; 2 cyc
             ora #$40     ; 2 cyc

From 65563b0e79b0b17f8de4a72795f82c36fdd66fbc Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Sat, 22 Aug 2026 16:45:09 -0700
Subject: [PATCH 22/27] Decent speedup in XE mode

Noticed that the separate addition for the low 1 bit case was
doing some dupe memory loads. Ended up making separate code
paths for even and odd values so the even saves two cycles
(from 52 down to 50 cycles) and the odd saves 14 cycles (from
69 down to 55 cycles). nice!

This gets the XE runtime on default view down from 3m38s to 3m33s,
a 5 second runtime improvement
---
 mandel-core.s | 69 +++++++++++++++++++++++++++++----------------------
 1 file changed, 40 insertions(+), 29 deletions(-)

diff --git a/mandel-core.s b/mandel-core.s
index 1f7234b..5159e2f 100644
--- a/mandel-core.s
+++ b/mandel-core.s
@@ -593,7 +593,9 @@ bank_switch_table:
 .macro imul8 dest, arg1, arg2, xe
     .if xe
         ; using 64KB lookup table
-        ; 52-69 cycles
+        ; 50-55 cycles
+        ; min: 11 + 9 + 9 + 21 = 50
+        ; max: 11 + 9 + 9 + 26 = 55
         ; clobbers x, y, dest, ptr
         .scope
             output = dest
@@ -612,15 +614,36 @@ bank_switch_table:
             ora #$40     ; 2 cyc
             sta ptr + 1  ; 3 cyc
 
-            ; copy the entry into output
+            ; mask off the low bit for the index, as the table contains
+            ; entries for every other arg1 value...
             lda arg1     ; 3 cyc
-            and #$fe     ; 2 cyc
             tay          ; 2 cyc
-            lda (ptr),y  ; 5 cyc
-            sta output   ; 3 cyc
-            iny          ; 2 cyc
-            lda (ptr),y  ; 5 cyc
-            sta output+1 ; 3 cyc
+            and #1       ; 2 cyc
+            bne odd      ; 2 cyc
+
+        even:
+            ; copy the entry into output
+            lda (ptr),y    ; 5 cyc
+            sta output     ; 3 cyc
+            iny            ; 2 cyc
+            lda (ptr),y    ; 5 cyc
+            sta output + 1 ; 3 cyc
+            jmp done       ; 3 cyc
+
+        odd:
+
+            ; skip the LSB for the index
+            dey            ; 2 cyc
+
+            ; add arg2 one last time for the skipped bit
+            txa            ; 2 cyc
+            clc            ; 2 cyc
+            adc (ptr), y   ; 5 cyc
+            sta output     ; 3 cyc
+            lda #0         ; 2 cyc
+            iny            ; 2 cyc
+            adc (ptr),y    ; 5 cyc
+            sta output + 1 ; 3 cyc
 
             ; note: we are not restoring memory to save 6 cycles!
             ; this means those 16kb have to be switched back to base RAM
@@ -629,18 +652,6 @@ bank_switch_table:
             ;;lda #$81     ; 2 cyc - disabled
             ;;sta PORTB    ; 4 cyc - disabled
 
-            ; check that 1 bit we skipped to fit into space
-            lda arg1     ; 3 cyc
-            and #1       ; 2 cyc
-            beq done     ; 2 cyc
-
-            ; add arg2 one last time for the skipped bit
-            clc          ; 2 cyc
-            txa          ; 2 cyc
-            adc output   ; 3 cyc
-            sta output   ; 3 cyc
-            add_carry output + 1 ; 2-7 cyc
-
         done:
         .endscope
     .else
@@ -776,8 +787,8 @@ inner_loop:
 
 ; min base mem: 81 * 4 + 22 * 2 + 10 + 6 = 384 cyc
 ; max base mem: 92 * 4 + 27 * 2 + 50 + 6 = 478 cyc
-; min ext-mem: 52 * 4 + 22 * 2 + 10 + 6 = 268 cyc
-; max ext-mem: 69 * 4 + 27 * 2 + 50 + 6 = 386 cyc
+; min ext-mem: 50 * 4 + 22 * 2 + 10 + 6 = 260 cyc
+; max ext-mem: 55 * 4 + 27 * 2 + 50 + 6 = 330 cyc
 .macro imul16_impl xe
     .local arg1
     .local arg2
@@ -796,18 +807,18 @@ inner_loop:
     ; h1*h2*256*256 + h1*l2*256 + h2*l1*256 + l1*l2
 
     ; l1 * l2
-    imul8 result, arg1, arg2, xe        ; 81-92 or 52-69
+    imul8 result, arg1, arg2, xe        ; 81-92 or 50-55
 
     ; 256 * 256 * h1 * h2
-    imul8 result + 2, arg1 + 1, arg2 + 1, xe ; 81-92 or 52-69
+    imul8 result + 2, arg1 + 1, arg2 + 1, xe ; 81-92 or 50-55
 
     ; 256 * h1 * l1
-    imul8 inter, arg1 + 1, arg2, xe     ; 81-92 or 52-69
+    imul8 inter, arg1 + 1, arg2, xe     ; 81-92 or 50-55
     add16 result + 1, result + 1, inter ; 20 cyc
     add_carry result + 3                ; 2-7 cyc
 
     ; 256 * l1 * h2
-    imul8 inter, arg1, arg2 + 1, xe     ; 81-92 or 52-69
+    imul8 inter, arg1, arg2 + 1, xe     ; 81-92 or 50-55
     add16 result + 1, result + 1, inter ; 20 cyc
     add_carry result + 3                ; 2-7 cyc
 
@@ -828,8 +839,8 @@ arg2_pos:
 
 ; min base ram: 5 + 19 * 2 + 81 + 22 * 2 + 6 = 174
 ; max base ram: 23 + 19 * 2 + 92 + 27 * 2 + 6 = 213
-; min ext ram: 5 + 19 * 2 + 52 + 22 * 2 + 6 = 145
-; max ext ram: 23 + 19 * 2 + 69 + 27 * 2 + 6 = 190
+; min ext ram: 5 + 19 * 2 + 50 + 22 * 2 + 6 = 143
+; max ext ram: 23 + 19 * 2 + 55 + 27 * 2 + 6 = 176
 .macro sqr16_impl xe
     .scope
         arg = FR0    ; 16-bit arg (clobbered)
@@ -855,7 +866,7 @@ arg2_pos:
         sqr8 result + 2, arg + 1  ; 19 cyc
 
         ; 2 * h * l * 256
-        imul8 inter, arg + 1, arg, xe        ; 81-92 / 52-69 cyc
+        imul8 inter, arg + 1, arg, xe        ; 81-92 / 50-55 cyc
         add16 result + 1, result + 1, inter  ; 20 cyc
         add_carry result + 3                 ; 2-7 cyc
         add16 result + 1, result + 1, inter  ; 20 cyc

From e029213c51da3bf1ff19dc13578c9220184099fa Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Sat, 22 Aug 2026 17:53:32 -0700
Subject: [PATCH 23/27] comment fix

---
 mandel-core.s | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mandel-core.s b/mandel-core.s
index 5159e2f..2777bda 100644
--- a/mandel-core.s
+++ b/mandel-core.s
@@ -812,7 +812,7 @@ inner_loop:
     ; 256 * 256 * h1 * h2
     imul8 result + 2, arg1 + 1, arg2 + 1, xe ; 81-92 or 50-55
 
-    ; 256 * h1 * l1
+    ; 256 * h1 * l2
     imul8 inter, arg1 + 1, arg2, xe     ; 81-92 or 50-55
     add16 result + 1, result + 1, inter ; 20 cyc
     add_carry result + 3                ; 2-7 cyc

From f3a92708d23d7822e4433f685313970a42047c9b Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Sat, 22 Aug 2026 18:48:05 -0700
Subject: [PATCH 24/27] unclobber arg in sqr16

this'll make it easier to use direct targets bypassing function args

costs 2 cycles on negatives in this version for now
but it should save us later
---
 mandel-core.s | 137 ++++++++++++++++++++++++++++++--------------------
 1 file changed, 82 insertions(+), 55 deletions(-)

diff --git a/mandel-core.s b/mandel-core.s
index 2777bda..64c5540 100644
--- a/mandel-core.s
+++ b/mandel-core.s
@@ -533,6 +533,20 @@ input_max:
     neg 4, arg
 .endmacro
 
+.macro copy_neg bytes, dest, arg
+    sec ; 2 cyc
+    .repeat bytes, byte ; 8 * byte cycles
+        lda #00         ; 2 cyc
+        sbc arg + byte  ; 3 cyc
+        sta dest + byte  ; 3 cyc
+    .endrepeat
+.endmacro
+
+; 18 cycles
+.macro copy_neg16 dest, arg
+    copy_neg 2, dest, arg
+.endmacro
+
 ; 11-27 + 18 * shift cycles
 ; 65-81 cycles for shift=3
 .macro shift_round_16 arg, shift
@@ -790,70 +804,58 @@ inner_loop:
 ; min ext-mem: 50 * 4 + 22 * 2 + 10 + 6 = 260 cyc
 ; max ext-mem: 55 * 4 + 27 * 2 + 50 + 6 = 330 cyc
 .macro imul16_impl xe
-    .local arg1
-    .local arg2
-    .local result
-    .local inter
-    .local arg1_pos
-    .local arg2_pos
-    arg1 = FR0   ; 16-bit arg (clobbered)
-    arg2 = FR1   ; 16-bit arg (clobbered)
-    result = FR2 ; 32-bit result
-    inter = temp2
+    .scope
+        arg1 = FR0    ; 16-bit arg
+        arg2 = FR1    ; 16-bit arg
+        result = FR2  ; 32-bit result (output)
+        inter = temp2 ; 16-bit temporary (clobbered)
 
-    ; h1l1 * h2l2
-    ; (h1*256 + l1) * (h2*256 + l2)
-    ; h1*256*(h2*256 + l2) + l1*(h2*256 + l2)
-    ; h1*h2*256*256 + h1*l2*256 + h2*l1*256 + l1*l2
+        ; h1l1 * h2l2
+        ; (h1*256 + l1) * (h2*256 + l2)
+        ; h1*256*(h2*256 + l2) + l1*(h2*256 + l2)
+        ; h1*h2*256*256 + h1*l2*256 + h2*l1*256 + l1*l2
 
-    ; l1 * l2
-    imul8 result, arg1, arg2, xe        ; 81-92 or 50-55
+        ; l1 * l2
+        imul8 result, arg1, arg2, xe        ; 81-92 or 50-55
 
-    ; 256 * 256 * h1 * h2
-    imul8 result + 2, arg1 + 1, arg2 + 1, xe ; 81-92 or 50-55
+        ; 256 * 256 * h1 * h2
+        imul8 result + 2, arg1 + 1, arg2 + 1, xe ; 81-92 or 50-55
 
-    ; 256 * h1 * l2
-    imul8 inter, arg1 + 1, arg2, xe     ; 81-92 or 50-55
-    add16 result + 1, result + 1, inter ; 20 cyc
-    add_carry result + 3                ; 2-7 cyc
+        ; 256 * h1 * l2
+        imul8 inter, arg1 + 1, arg2, xe     ; 81-92 or 50-55
+        add16 result + 1, result + 1, inter ; 20 cyc
+        add_carry result + 3                ; 2-7 cyc
 
-    ; 256 * l1 * h2
-    imul8 inter, arg1, arg2 + 1, xe     ; 81-92 or 50-55
-    add16 result + 1, result + 1, inter ; 20 cyc
-    add_carry result + 3                ; 2-7 cyc
+        ; 256 * l1 * h2
+        imul8 inter, arg1, arg2 + 1, xe     ; 81-92 or 50-55
+        add16 result + 1, result + 1, inter ; 20 cyc
+        add_carry result + 3                ; 2-7 cyc
 
-    ; In case of negative inputs, adjust high word
-    ; https://stackoverflow.com/a/28827013
-    ; 10-50 cycles
-    lda arg1 + 1                       ; 3 cyc
-    bpl arg1_pos                       ; 2 cyc
-    sub16 result + 2, result + 2, arg2 ; 20 cyc
-arg1_pos:
-    lda arg2 + 1                       ; 3 cyc
-    bpl arg2_pos                       ; 2 cyc
-    sub16 result + 2, result + 2, arg1 ; 20 cyc
-arg2_pos:
+        ; In case of negative inputs, adjust high word
+        ; https://stackoverflow.com/a/28827013
+        ; 10-50 cycles
+        lda arg1 + 1                       ; 3 cyc
+        bpl arg1_pos                       ; 2 cyc
+        sub16 result + 2, result + 2, arg2 ; 20 cyc
+    arg1_pos:
 
-    rts ; 6 cyc
+        lda arg2 + 1                       ; 3 cyc
+        bpl arg2_pos                       ; 2 cyc
+        sub16 result + 2, result + 2, arg1 ; 20 cyc
+    arg2_pos:
+
+        rts ; 6 cyc
+    .endscope
 .endmacro
 
-; min base ram: 5 + 19 * 2 + 81 + 22 * 2 + 6 = 174
-; max base ram: 23 + 19 * 2 + 92 + 27 * 2 + 6 = 213
-; min ext ram: 5 + 19 * 2 + 50 + 22 * 2 + 6 = 143
-; max ext ram: 23 + 19 * 2 + 55 + 27 * 2 + 6 = 176
-.macro sqr16_impl xe
+
+; min base: 19 * 2 + 81 + 22 * 2 = 163
+; max base: 19 * 2 + 92 + 27 * 2 = 184
+; min ext: 19 * 2 + 50 + 22 * 2 = 132
+; max ext: 19 * 2 + 55 + 27 * 2 = 147
+.macro sqr16_impl_inner result, arg, xe
     .scope
-        arg = FR0    ; 16-bit arg (clobbered)
-        result = FR2 ; 32-bit result
-        ;inter = temp2
-        inter = FR1
-
-        ; 5-23 cycles
-        lda arg + 1  ; 3 cyc
-        bpl arg_pos  ; 2 cyc
-        neg16 arg    ; 18 cyc
-    arg_pos:
-
+    inter = temp2
         ; hl * hl
         ; (h*256 + l) * (h*256 + l)
         ; h*256*(h*256 + l) + l*(h*256 + l)
@@ -871,8 +873,33 @@ arg2_pos:
         add_carry result + 3                 ; 2-7 cyc
         add16 result + 1, result + 1, inter  ; 20 cyc
         add_carry result + 3                 ; 2-7 cyc
+    .endscope
+.endmacro
 
-        rts ; 6 cyc
+
+; min base ram: 5 + 163 + 6 = 174
+; max base ram: 7 + 184 + 18 + 6 = 215
+; min ext ram: 5 + 132 + 6 = 143
+; max ext ram: 7 + 147 + 18 + 6 = 178
+.macro sqr16_impl xe
+    .scope
+        arg = FR0    ; 16-bit arg
+        negated = FR1
+        result = FR2 ; 32-bit result
+
+        ; 5-7 cycles
+        lda arg + 1                ; 3 cyc
+        bpl arg_pos                ; 2 cyc
+        jmp arg_neg                ; 3 cyc
+
+    arg_pos:
+        sqr16_impl_inner result, arg, xe      ; 163-184 / 132-147 cyc
+        rts                                   ; 6 cyc
+
+    arg_neg:
+        copy_neg16 negated, arg               ; 18 cyc
+        sqr16_impl_inner result, negated, xe  ; 163-184 / 132-147 cyc
+        rts                                   ; 6 cyc
     .endscope
 .endmacro
 

From d93dd2e6a6b6c9adedd9cb718c5227f0bff62558 Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Sun, 23 Aug 2026 15:18:25 -0700
Subject: [PATCH 25/27] step 1: sqr16_impl and imul16_impl take argument
 addresses

first step to removing function call overhead
---
 mandel-core.s | 49 ++++++++++++++++++++++++++-----------------------
 1 file changed, 26 insertions(+), 23 deletions(-)

diff --git a/mandel-core.s b/mandel-core.s
index 64c5540..2e1c8b2 100644
--- a/mandel-core.s
+++ b/mandel-core.s
@@ -799,15 +799,15 @@ inner_loop:
 
 .endproc
 
-; min base mem: 81 * 4 + 22 * 2 + 10 + 6 = 384 cyc
-; max base mem: 92 * 4 + 27 * 2 + 50 + 6 = 478 cyc
-; min ext-mem: 50 * 4 + 22 * 2 + 10 + 6 = 260 cyc
-; max ext-mem: 55 * 4 + 27 * 2 + 50 + 6 = 330 cyc
-.macro imul16_impl xe
+; min base mem: 81 * 4 + 22 * 2 + 10 = 378 cyc
+; max base mem: 92 * 4 + 27 * 2 + 50 = 472 cyc
+; min ext-mem: 50 * 4 + 22 * 2 + 10 = 254 cyc
+; max ext-mem: 55 * 4 + 27 * 2 + 50 = 324 cyc
+.macro imul16_impl result, arg1, arg2, xe
     .scope
-        arg1 = FR0    ; 16-bit arg
-        arg2 = FR1    ; 16-bit arg
-        result = FR2  ; 32-bit result (output)
+        ;arg1         ; 16-bit arg
+        ;arg2         ; 16-bit arg
+        ;result       ; 32-bit result (output)
         inter = temp2 ; 16-bit temporary (clobbered)
 
         ; h1l1 * h2l2
@@ -843,8 +843,6 @@ inner_loop:
         bpl arg2_pos                       ; 2 cyc
         sub16 result + 2, result + 2, arg1 ; 20 cyc
     arg2_pos:
-
-        rts ; 6 cyc
     .endscope
 .endmacro
 
@@ -877,15 +875,15 @@ inner_loop:
 .endmacro
 
 
-; min base ram: 5 + 163 + 6 = 174
-; max base ram: 7 + 184 + 18 + 6 = 215
-; min ext ram: 5 + 132 + 6 = 143
-; max ext ram: 7 + 147 + 18 + 6 = 178
-.macro sqr16_impl xe
+; min base ram: 5 + 163 + 3 = 171
+; max base ram: 7 + 184 + 18 = 209
+; min ext ram: 5 + 132 + 3 = 140
+; max ext ram: 7 + 147 + 18 = 172
+.macro sqr16_impl result, arg, xe
     .scope
-        arg = FR0    ; 16-bit arg
+        ; arg        ; 16-bit arg
         negated = FR1
-        result = FR2 ; 32-bit result
+        ; result     ; 32-bit result
 
         ; 5-7 cycles
         lda arg + 1                ; 3 cyc
@@ -894,29 +892,34 @@ inner_loop:
 
     arg_pos:
         sqr16_impl_inner result, arg, xe      ; 163-184 / 132-147 cyc
-        rts                                   ; 6 cyc
+        jmp done                              ; 3 cyc
 
     arg_neg:
         copy_neg16 negated, arg               ; 18 cyc
         sqr16_impl_inner result, negated, xe  ; 163-184 / 132-147 cyc
-        rts                                   ; 6 cyc
+
+    done:
     .endscope
 .endmacro
 
 .proc imul16_func
-    imul16_impl 0
+    imul16_impl FR2, FR0, FR1, 0
+    rts
 .endproc
 
 .proc imul16xe_func
-    imul16_impl 1
+    imul16_impl FR2, FR0, FR1, 1
+    rts
 .endproc
 
 .proc sqr16_func
-    sqr16_impl 0
+    sqr16_impl FR2, FR0, 0
+    rts
 .endproc
 
 .proc sqr16xe_func
-    sqr16_impl 1
+    sqr16_impl FR2, FR0, 1
+    rts
 .endproc
 
 ; 11-27 cycles

From e58df379e72ced940342df9a34b8aeee53480355 Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Sun, 23 Aug 2026 15:48:48 -0700
Subject: [PATCH 26/27] step 2: break out the multiplication hotspot

mandelbrot_hotspot_impl macro calls through to the
sqr16_impl and imul16_impl macros with the xe mode

this is backed by two realized functions, as
mandelbrot_hotspot and mandelbrot_hotspot_xe

these are also called via direct jmp instead of jsr/rts
because there's only one call site so we can save 6 cycles
per iteration by jmp/jmp

could save 6 more cycles per iter by specializing all of
the mandelbrot proc but there isn't room in ram right now

sqr16_func is removed as it is unused and we ran out of
code space adding the hotspot's extra implementations

imul16_func is kept, as it's called via zoom_factor
in a couple of places. this forwards to the xe version
at a cost of 3 cycles, as the call sites aren't patched
---
 mandel-core.s | 85 +++++++++++++++++++++++++++++----------------------
 1 file changed, 48 insertions(+), 37 deletions(-)

diff --git a/mandel-core.s b/mandel-core.s
index 2e1c8b2..17ecfc4 100644
--- a/mandel-core.s
+++ b/mandel-core.s
@@ -558,8 +558,6 @@ input_max:
 
 ; input: arg1, arg2 as fixed4.12
 ; output: dest as fixed8.24
-; patch point jsr at 16 bytes in
-imul16_patch_offset = 16
 .macro imul16 dest, arg1, arg2
     copy16 FR0, arg1  ; 12 cyc
     copy16 FR1, arg2  ; 12 cyc
@@ -569,13 +567,11 @@ imul16_patch_offset = 16
 
 ; input: arg as fixed4.12
 ; output: dest as fixed8.24
-; patch point jsr at 8 bytes in
-sqr16_patch_offset = 8
-.macro sqr16 dest, arg
-    copy16 FR0, arg   ; 12 cyc
-    jsr sqr16_func    ; ? cyc
-    copy32 dest, FR2  ; 24 cyc
-.endmacro
+;.macro sqr16 dest, arg
+;    copy16 FR0, arg   ; 12 cyc
+;    jsr sqr16_func    ; ? cyc
+;    copy32 dest, FR2  ; 24 cyc
+;.endmacro
 
 ; input: arg as u8
 ; output: dest as u16
@@ -912,15 +908,15 @@ inner_loop:
     rts
 .endproc
 
-.proc sqr16_func
-    sqr16_impl FR2, FR0, 0
-    rts
-.endproc
+;.proc sqr16_func
+;    sqr16_impl FR2, FR0, 0
+;    rts
+;.endproc
 
-.proc sqr16xe_func
-    sqr16_impl FR2, FR0, 1
-    rts
-.endproc
+;.proc sqr16xe_func
+;    sqr16_impl FR2, FR0, 1
+;    rts
+;.endproc
 
 ; 11-27 cycles
 .macro round16 arg
@@ -1160,16 +1156,11 @@ keep_going:
     shift_round_16 zy, 3
 
     ; zx_2 = zx * zx
-fixup_sqr16_1:
-    sqr16 zx_2, zx + 2
-
     ; zy_2 = zy * zy
-fixup_sqr16_2:
-    sqr16 zy_2, zy + 2
-
     ; zx_zy = zx * zy
-fixup_imul16_1:
-    imul16 zx_zy, zx + 2, zy + 2
+fixup_mandelbrot_hotspot:
+    jmp mandelbrot_hotspot
+after_mandelbrot_hotspot:
 
     ; dist = zx_2 + zy_2
     add32 dist, zx_2, zy_2
@@ -1265,6 +1256,27 @@ next:
 
 .endproc
 
+.macro mandelbrot_hotspot_impl xe 
+    ; zx_2 = zx * zx
+    sqr16_impl zx_2, zx + 2, xe
+
+    ; zy_2 = zy * zy
+    sqr16_impl zy_2, zy + 2, xe
+
+    ; zx_zy = zx * zy
+    imul16_impl zx_zy, zx + 2, zy + 2, xe
+
+    jmp mandelbrot::after_mandelbrot_hotspot
+.endmacro
+
+.proc mandelbrot_hotspot
+    mandelbrot_hotspot_impl 0
+.endproc
+
+.proc mandelbrot_hotspot_xe
+    mandelbrot_hotspot_impl 1
+.endproc
+
 .macro scale_zoom dest
     ; clobbers X, flags
     .local cont
@@ -2192,22 +2204,21 @@ init:
     sta imul16_func
     lda #.lobyte(imul16xe_func)
     sta imul16_func + 1
-    sta mandelbrot::fixup_imul16_1 + imul16_patch_offset + 1
     lda #.hibyte(imul16xe_func)
     sta imul16_func + 2
-    sta mandelbrot::fixup_imul16_1 + imul16_patch_offset + 2
 
     ; ditto for sqr16_func -> sqr16xe_func
-    lda #$4c ; 'jmp' opcode
-    sta sqr16_func
-    lda #.lobyte(sqr16xe_func)
-    sta sqr16_func + 1
-    sta mandelbrot::fixup_sqr16_1 + sqr16_patch_offset + 1
-    sta mandelbrot::fixup_sqr16_2 + sqr16_patch_offset + 1
-    lda #.hibyte(sqr16xe_func)
-    sta sqr16_func + 2
-    sta mandelbrot::fixup_sqr16_1 + sqr16_patch_offset + 2
-    sta mandelbrot::fixup_sqr16_2 + sqr16_patch_offset + 2
+    ;lda #$4c ; 'jmp' opcode
+    ;sta sqr16_func
+    ;lda #.lobyte(sqr16xe_func)
+    ;sta sqr16_func + 1
+    ;lda #.hibyte(sqr16xe_func)
+    ;sta sqr16_func + 2
+
+    lda #.lobyte(mandelbrot_hotspot_xe)
+    sta mandelbrot::fixup_mandelbrot_hotspot + 1
+    lda #.hibyte(mandelbrot_hotspot_xe)
+    sta mandelbrot::fixup_mandelbrot_hotspot + 2
 
 
     ; create the lookup table

From 2ed28e5590e47c24f9a166272d95a08f1ddec8d2 Mon Sep 17 00:00:00 2001
From: Brooke Vibber <bvibber@pobox.com>
Date: Sun, 23 Aug 2026 16:08:18 -0700
Subject: [PATCH 27/27] drop some old commented out code

---
 mandel-core.s | 8 --------
 1 file changed, 8 deletions(-)

diff --git a/mandel-core.s b/mandel-core.s
index 17ecfc4..a43894d 100644
--- a/mandel-core.s
+++ b/mandel-core.s
@@ -1051,14 +1051,6 @@ common:
     ; zx_zy = 0
     ; dist = 0
     ; iter = 0
-;    lda #00
-;    ldx #(iter - zx + 1)
-;initloop:
-;    sta zx - 1,x
-;    dex
-;    bne initloop
-;    sta z_buffer_start
-;    sta z_buffer_end
 
     lda #00
     sta zx