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WIP imul8 via table experiments

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planning to try a 64KB table of 8x7-bit multiplies in the high memory
on a 130XE or other high-memory-capable machine

not yet working or finished

too many cycles of overhead per invocation
This commit is contained in:
Brooke Vibber 2024-12-25 10:51:27 -08:00
commit 405cec6d51
2 changed files with 133 additions and 32 deletions
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mandel.s
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@ -372,51 +372,58 @@ fill_masks:
.local under256
.local next
.local small_product
; circa 92 cycles? this doesn't seem right
.scope
mul_factor_a = arg1
mul_factor_x = arg2
mul_product_lo = dest
mul_product_hi = dest + 1
lda mul_factor_a ; setup: 6 cycles
;ldx mul_factor_x
lda mul_factor_a ; 3 cyc
clc ; (a + x)^2/2: 23 cycles
adc mul_factor_x
tax
bcc under256
lda mul_hibyte512,x
bcs next
; (a + x)^2/2
clc ; 2 cyc
adc mul_factor_x ; 3 cyc
tax ; 2 cyc
bcc under256 ; 2 cyc
lda mul_hibyte512,x ; 4 cyc
bcs next ; 2 cyc
under256:
lda mul_hibyte256,x
sec
lda mul_hibyte256,x ; 4 cyc
sec ; 2 cyc
next:
sta mul_product_hi
lda mul_lobyte256,x
sta mul_product_hi ; 3 cyc
lda mul_lobyte256,x ; 4 cyc
ldx mul_factor_a ; - a^2/2: 20 cycles
sbc mul_lobyte256,x
sta mul_product_lo
lda mul_product_hi
sbc mul_hibyte256,x
sta mul_product_hi
; - a^2/2
ldx mul_factor_a ; 3 cyc
sbc mul_lobyte256,x ; 4 cyc
sta mul_product_lo ; 3 cyc
lda mul_product_hi ; 3 cyc
sbc mul_hibyte256,x ; 4 cyc
sta mul_product_hi ; 3 cyc
ldx mul_factor_x ; + x & a & 1: 22 cycles
txa ; (this is a kludge to correct a
and mul_factor_a ; roundoff error that makes odd * odd too low)
and #1
; + x & a & 1:
; (this is a kludge to correct a
; roundoff error that makes odd * odd too low)
ldx mul_factor_x ; 3 cyc
txa ; 2 cyc
and mul_factor_a ; 3 cyc
and #1 ; 2 cyc
clc
adc mul_product_lo
bcc small_product
inc mul_product_hi
clc ; 2 cyc
adc mul_product_lo ; 3 cyc
bcc small_product ; 2 cyc
inc mul_product_hi ; 5 cyc
; - x^2/2
small_product:
sec ; - x^2/2: 25 cycles
sbc mul_lobyte256,x
sta mul_product_lo
lda mul_product_hi
sbc mul_hibyte256,x
sta mul_product_hi
sec ; 2 cyc
sbc mul_lobyte256,x ; 4 cyc
sta mul_product_lo ; 3 cyc
lda mul_product_hi ; 3 cyc
sbc mul_hibyte256,x ; 4 cyc
sta mul_product_hi ; 3 cyc
.endscope
.endmacro