brooke/mandel-6502
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brooke:fastmul
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compare: brooke:9682b4a6b38620ff1ec939087426571d368d0419
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brooke:fastmul
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1 changed files with 12 additions and 27 deletions
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mandel.s
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@ -30,18 +30,15 @@ FRX = $ec
.endmacro .endmacro
; inner loop for imul16 ; inner loop for imul16
; bitnum < 8: 25 or 41 cycles ; 24 to 44 cycles
; bitnum >= 8: 30 or 46 cycles
.macro bitmul16 arg1, arg2, result, bitnum .macro bitmul16 arg1, arg2, result, bitnum
.local zero
.local one
.local next .local next
; does 16-bit adds ; does 16-bit adds
; arg1 must be 0 or positive ; arg1 must be 0 or positive
; arg2 must be 0 or positive ; arg2 must be 0 or positive
; 7 cycles up to the branch clc ; 2 cyc
; check if arg1 has 0 or 1 bit in this place ; check if arg1 has 0 or 1 bit in this place
; 5 cycles either way ; 5 cycles either way
@ -52,29 +49,21 @@ FRX = $ec
lda arg1 + 1 ; 3 cyc lda arg1 + 1 ; 3 cyc
and #(1 << (bitnum - 8)) ; 2 cyc and #(1 << (bitnum - 8)) ; 2 cyc
.endif .endif
bne one ; 2 cyc beq next ; 2 cyc
zero: ; 18 cyc, 23 cyc
lsr result + 3 ; 5 cyc
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
jmp next ; 3 cyc
one: ; 32 cyc, 37 cyc
; 16-bit add on the top bits ; 16-bit add on the top bits
clc ; 2 cyc
lda result + 2 ; 3 cyc lda result + 2 ; 3 cyc
adc arg2 ; 3 cyc adc arg2 ; 3 cyc
sta result + 2 ; 3 cyc sta result + 2 ; 3 cyc
lda result + 3 ; 3 cyc lda result + 3 ; 3 cyc
adc arg2 + 1 ; 3 cyc adc arg2 + 1 ; 3 cyc
ror a ; 2 cyc ror a ; 2 cyc - get a jump on the shift
sta result + 3 ; 3 cyc sta result + 3 ; 3 cyc
; Shift the 32-bit result down by one bit,
; saving the previous carry.
ror result + 3 ; 5 cyc
next:
ror result + 2 ; 5 cyc ror result + 2 ; 5 cyc
ror result + 1 ; 5 cyc ror result + 1 ; 5 cyc
.if bitnum >= 8 .if bitnum >= 8
@ -82,9 +71,6 @@ one: ; 32 cyc, 37 cyc
; when it's all uninitialized data ; when it's all uninitialized data
ror result ; 5 cyc ror result ; 5 cyc
.endif .endif
next:
.endmacro .endmacro
; 5 to 25 cycles ; 5 to 25 cycles
@ -121,8 +107,8 @@ positive:
; of a larger routine ; of a larger routine
; 424 to 672 cycles ; 424 to 672 cycles
.repeat 16, bitnum .repeat 16, bitnum
; first half: 22 to 40 cycles ; first half: 24 to 40 cycles
; second half: 29 to 47 cycles ; second half: 29 to 44 cycles
bitmul16 arg1, arg2, result, bitnum bitmul16 arg1, arg2, result, bitnum
.endrepeat .endrepeat
@ -167,7 +153,7 @@ loop:
.proc start .proc start
looplong: loop:
; FR0 = 5 ; FR0 = 5
; FR1 = -3 ; FR1 = -3
lda #5 lda #5
@ -182,6 +168,5 @@ looplong:
jsr imul16 jsr imul16
; should have 32-bit -15 in FR2 ; should have 32-bit -15 in FR2
loop:
jmp loop jmp loop
.endproc .endproc