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update round & sketch out the iter cycle count

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Brooke Vibber 2023-01-05 11:32:15 -08:00
parent 7f70f14fc2
commit 2340f8210e
1 changed files with 19 additions and 118 deletions
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mandel.s
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@ -176,137 +176,38 @@ next:
.endmacro
.macro round16_addsub arg
; Round top 16 bits of 32-bit fixed-point number in-place
.local zero
.local one
.local positive
.local negative
.local neg2
.local next
; no round - 5 cycles
; one, pos - 28 cycles
; one, neg - 31 cycles
; average = 5 / 2 + (28 + 31) / 4
; = 5/2 + 59 / 4
; = 2.5 + 14.75
; = 17.25 cycles average on evenly distributed data
lda arg + 1 ; 3 cyc
bpl zero ; 2 cyc
one:
; check sign bit
lda arg + 3 ; 3 cyc
bpl positive ; 2 cyc
negative:
sec ; 2 cyc
lda arg + 2 ; 3 cyc
sbc #1 ; 2 cyc
sta arg + 2 ; 3 cyc
lda arg + 3 ; 3 cyc
sbc #0 ; 2 cyc
sta arg + 3 ; 3 cyc
jmp next ; 3 cyc
positive:
clc ; 2 cyc
lda arg + 2 ; 3 cyc
adc #1 ; 2 cyc
sta arg + 2 ; 3 cyc
lda arg + 3 ; 3 cyc
adc #0 ; 2 cyc
sta arg + 3 ; 3 cyc
zero:
next:
.endmacro
.macro round16_addsub_copy arg, dest
; Round top 16 bits of 32-bit fixed-point number and copy it
.local zero
.local one
.local positive
.local negative
.local neg2
.local next
; no round - 17 cycles
; round, positive - 31 cycles
; round, negative - 31 cycles
; average = 17 / 2 + (31 + 31) / 4
; = 17 / 2 + 62 / 4
; = 24 cycles average
;
; compare with 13.75 cyc in-place plus three copies at 12 cycles
; 13.75 + 36 = 49.75 (41 - 64)
; versus three rounds+copies: 72 (51 - 93)
lda arg + 1 ; 3 cyc
bpl zero ; 2 cyc
one:
; check sign bit
lda arg + 3 ; 3 cyc
bpl positive ; 2 cyc
negative:
sec ; 2 cyc
lda arg + 2 ; 3 cyc
sbc #1 ; 2 cyc
sta dest ; 3 cyc
lda arg + 3 ; 3 cyc
sbc #0 ; 2 cyc
jmp next ; 3 cyc
positive:
clc ; 2 cyc
lda arg + 2 ; 3 cyc
adc #1 ; 2 cyc
sta dest ; 3 cyc
lda arg + 3 ; 3 cyc
adc #0 ; 2 cyc
jmp next ; 3 cyc
zero:
lda arg + 2 ; 3 cyc
sta dest ; 3 cyc
lda arg + 3 ; 3 cyc
next:
sta dest + 2 ; 3 cyc
.endmacro
.proc iter
; (cx and cy should be pre-scaled to 6.26 fixed point)
; still working on the fixed-point
; should we just use 16-bit adds?
; does that require extra rounding?
; is the integer precision right?
; (cx and cy should be pre-scaled to 4.12 fixed point - -8..+7.9)
; zx = 0
; zy = 0
; zx_2 = 0
; zy_2 = 0
; zx_zy = 0
; still working on the fixed-point
loop:
; iters++
; 1627 - 2603 cyc
; 6.26:
; zx = zx_2 + zy_2 + cx
; zy = zx_zy + zx_zy + cy
; round to 6.10.
; iters++ = 2 cyc
; 12.20:
; zx_2 = zx * zx
; zy_2 = zy * zy
; dist = zx_2 + zy_2
; if dist >= 4 break, else continue iterating
; 4.12: (-8 .. +7.9)
; zx = zx_2 + zy_2 + cx = 3 * 20 = 60 cyc
; zy = zx_zy + zx_zy + cy = 3 * 20 = 60 cyc
; round zx_2, zy_2, dist to 6.26
; 8.24:
; zx_2 = zx * zx = 470 - 780 cyc
; zy_2 = zy * zy = 470 - 780 cyc
; zx_zy = zx * zy = 470 - 780 cyc
; dist = zx_2 + zy_2 = 38 cyc
; if dist >= 4 break, else continue iterating = 7 cyc
; shift and round zx_2, zy_2, dist up to 4.12 = 2 * (20 + 5) - 2 * (20 + 28) = 50 - 96 cyc
; if may be in the lake, look for looping output with a small buffer
; as an optimization vs running to max iters