sixth viewport

skip experimental 6th viewport that got forgotten
and limit max zoom to 7 (range 0-7) which is what looks good

Makefile

@@ -2,8 +2,8 @@
 
 all : mandel.xex
 
-mandel.xex : mandel.o tables.o
+mandel.xex : mandel.o tables.o atari-asm-xex.cfg
-	ld65 -C ./atari-asm-xex.cfg -o $@ $+
+	ld65 -C ./atari-asm-xex.cfg -o $@ mandel.o tables.o
 
 %.o : %.s
 	ca65 -o $@ $<

atari-asm-xex.cfg

@@ -0,0 +1,28 @@
+FEATURES {
+    STARTADDRESS: default = $2E00;
+}
+SYMBOLS {
+    __STARTADDRESS__: type = export, value = %S;
+}
+MEMORY {
+    ZP:      file = "", define = yes, start = $0082, size = $007E;
+    MAIN:    file = %O, define = yes, start = %S,    size = $4000 - %S;
+    # Keep $4000-7fff clear for expanded RAM access window
+    TABLES:  file = %O, define = yes, start = $8000, size = $a000 - $8000;
+    # Keep $a000-$bfff clear for BASIC cartridge
+}
+FILES {
+    %O: format = atari;
+}
+FORMATS {
+    atari: runad = start;
+}
+SEGMENTS {
+    ZEROPAGE: load = ZP,      type = zp,  optional = yes;
+    EXTZP:    load = ZP,      type = zp,  optional = yes; # to enable modules to be able to link to C and assembler programs
+    CODE:     load = MAIN,    type = rw,                  define = yes;
+    RODATA:   load = MAIN,    type = ro   optional = yes;
+    DATA:     load = MAIN,    type = rw   optional = yes;
+    BSS:      load = MAIN,    type = bss, optional = yes, define = yes;
+    TABLES:   load = TABLES,  type = ro,  optional = yes, align = 256;
+}

imul8xe.s

@@ -1,175 +0,0 @@
-FR0    = $d4 ; float48
-PORTB = $d301
-
-
-EXTENDED_RAM = $4000 ; 16KiB bank on the XE
-
-; lookup table for top byte -> PORTB value for bank-switch
-.align 256
-bankswitch:
-    .repeat 256, i
-        .byte ((i & $c0) >> 5) | $c1
-    .endrepeat
-
-; 58-77 cycles
-; clobbers x, y, dest to dest + 3
-.macro imul8xe dest, arg1, arg2
-.local done
-.local output
-.local ptr
-
-    output = dest
-    ptr = dest + 2 ; scratch space assumed
-
-    ; bottom 14 bits except the LSB are the per-bank table index
-    ; add $4000 for the bank pointer
-    lda arg1     ; 3 cyc
-    and #$fe     ; 2 cyc
-    sta ptr      ; 3 cyc
-    lda arg2     ; 3 cyc
-    and #$3f     ; 2 cyc
-    clc          ; 2 cyc
-    adc #$40     ; 2 cyc
-    sta ptr + 1  ; 3 cyc
-    
-    ; top 2 bits are the table bank selector
-    ldx arg2          ; 3 cyc
-    lda bank_switch,x ; 4 cyc
-    sta PORTB         ; 4 cyc
-
-
-    ; copy the entry into output
-    ldy #0       ; 2 cyc
-    lda (ptr),y  ; 5 cyc
-    sta output   ; 3 cyc
-    iny          ; 2 cyc
-    lda (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
-    ; if we need to use them anywhere else
-    ;;; restore memory
-    ;;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 the second param one last time for the skipped bit
-    clc          ; 2 cyc
-    lda arg2     ; 3 cyc
-    adc output   ; 3 cyc
-    sta output   ; 3 cyc
-    lda #0       ; 2 cyc
-    adc output+1 ; 3 cyc
-    sta output+1 ; 3 cyc
-
-done:
-.endmacro
-
-.macro bank_switch bank
-    lda #((bank << 1) | $c1)
-    sta PORTB
-.endmacro
-
-proc imul8xe_init
-
-    ; go through the input set, in four 16KB chunks
-
-    arg1 = FR1
-    arg2 = FR2
-    result = FR0
-
-    lda #$00
-    sta arg1
-    sta arg2
-
-    ; $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
-; output: new multipliers in temp
-; clobbers: temp, temp2
-proc imul8xe_init_section
-    arg1 = FR1
-    arg2 = FR2
-    result = FR0
-    ptr = temp2
-
-    lda #$00
-    sta ptr
-    lda #$40
-    sta ptr + 1
-
-    ldx #0
-    ldy #0
-
-    ; outer loop: $00 -> $3f
-outer_loop:
-
-    ; reset result to 0
-    lda #0
-    sta result
-    sta result + 1
-
-    ; inner loop: $00 -> $ff
-inner_loop:
-
-    ; copy result to data set
-    lda result
-    sta (ptr),y
-    lda result + 1
-    sta (ptr),y
-
-    ; result += 2 * arg2
-    clc
-    lda arg2
-    adc result
-    sta result
-    lda #0
-    adc result + 1
-    sta result
-    lda arg2
-    adc result
-    sta result
-    lda #0
-    adc result + 1
-    sta result
-
-    ; inner loop check
-    inc arg1
-    inc arg1
-    inc ptr
-    inc ptr
-    bne inner_loop
-
-    ; outer loop check
-    inc arg2
-    inc ptr + 1
-    lda ptr + 1
-    cmp #$40
-    bne outer_loop
-
-    rts
-
-endproc

readme.md

@@ -14,33 +14,37 @@ Non-goals:
 
 Enjoy! I'll probably work on this off and on for the next few weeks until I've got it producing fractals.
 
--- brooke, january 2023 - february 2024
+-- brooke, january 2023 - december 2024
 
 ## Current state
 
-Basic rendering is functional, but no interactive behavior (zoom/pan) or benchmarking is done yet.
+Basic rendering is functional, with interactive zoom/pan (+/-/arrows) and 6 preset viewports via the number keys.
 
-The 16-bit signed integer multiplication works; it takes two 16-bit inputs and emits one 32-bit output in the zero page, using the Atari OS ROM's floating point registers as workspaces. Inputs are clobbered.
+The 16-bit signed integer multiplication takes two 16-bit inputs and emits one 32-bit output in the zero page, using the Atari OS ROM's floating point registers as workspaces. Inputs are clobbered.
 
-The main loop is a basic add-and-shift, using 16-bit adds which requires flipping the sign of negative inputs (otherwise you'd have to add all those sign-extension bits). Runs in 470-780 cycles depending on input.
+* 16-bit multiplies are decomposed into 4 8-bit unsigned multiplies and some addition
+* an optimized case for squares uses a table of 8-bit squares to reduce the number of 8-bit multiplication sub-ops
+* when expanded RAM is available as on 130XE, a 64KB 8-bit multiplication table accelerates the remaining multiplications
+* without expanded RAM, a table of half-squares is used to implement the algorithm from https://everything2.com/title/Fast+6502+multiplication
 
-The mandelbrot calculations are done using 4.12-precision fixed point numbers. It may be possible to squish this down to 3.13.
+The mandelbrot calculations are done using 3.13-precision fixed point numbers with 6.26-precision intermediates.
 
 Iterations are capped at 255.
 
 The pixels are run in a progressive layout to get the basic shape on screen faster.
 
-## Next steps
+There is a running counter of ms/px using the vertical blank interrupts as a timer, used to track our progress. :D
 
-Add a running counter of ms/px using the vertical blank interrupts as a timer. This'll show how further work improves it!
+There's a check for cycles in (zx,zy) output when in the 'lake'; if values repeat, they cannot escape. This is a big time saver in fractint.
 
-Check for cycles in (zx,zy) output when in the 'lake'; if values repeat, they cannot escape. This is a big time saver in fractint.
+There's some cute color cycling.
-
-I may be able to do a faster multiply using tables of squares for 8-bit component multiplication.
-(done)
 
 ## Deps and build instructions
 
 I'm using `ca65` as a macro assembler, and have a Unix-style `Makefile` for building. Should work fairly easily on Linux and Mac. Might work on "raw" Windows but I use WSL for that.
 
 Currently produces a `.xex` executable, which can be booted up in common Atari emulators and some i/o devices.
+
+## Todo
+
+See ideas in `todo.md`.

tables.js

@@ -22,7 +22,10 @@ console.log(
 .export mul_lobyte256
 .export mul_hibyte256
 .export mul_hibyte512
+.export sqr_lobyte
+.export sqr_hibyte
 
+; (i * i + 1) / 2 for the multiplier
 .align 256
 mul_lobyte256:
 ${db((i) => squares[i] & 0xff)}
@@ -35,4 +38,13 @@ ${db((i) => (squares[i] >> 8) & 0xff)}
 mul_hibyte512:
 ${db((i) => (squares[i + 256] >> 8) & 0xff)}
 
+; (i * i) for the plain squares
+.align 256
+sqr_lobyte:
+${db((i) => (i * i) & 0xff)}
+
+.align 256
+sqr_hibyte:
+${db((i) => ((i * i) >> 8) & 0xff)}
+
 `);

todo.md

@@ -0,0 +1,12 @@
+things to try:
+
+* skip add on the top-byte multiply in sqr8/mul8
+  * should save a few cycles, suggestion by jamey
+
+* patch the entire expanded-ram imul8xe on top of imul8 to avoid the 3-cycle thunk penalty :D
+
+* y-axis mirror optimization
+
+* extract viewport for display & re-input via keyboard
+
+* fujinet screenshot/viewport uploader