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slightly faster integer bytes multiplication routine

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Irmen de Jong
2023-08-14 16:58:44 +02:00
parent bbb6c53457
commit 4c8beefdcb
2 changed files with 203 additions and 51 deletions
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68
compiler/res/prog8lib/math.asm
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@@ -10,37 +10,47 @@
multiply_bytes .proc
; -- multiply 2 bytes A and Y, result as byte in A (signed or unsigned)
sta P8ZP_SCRATCH_B1 ; num1
sty P8ZP_SCRATCH_REG ; num2
lda #0
beq _enterloop
_doAdd clc
adc P8ZP_SCRATCH_B1
_loop asl P8ZP_SCRATCH_B1
_enterloop lsr P8ZP_SCRATCH_REG
bcs _doAdd
bne _loop
rts
.pend
; https://github.com/TobyLobster/multiply_test/blob/main/tests/mult29.a
_multiplicand = P8ZP_SCRATCH_B1
_multiplier = P8ZP_SCRATCH_REG
multiply_bytes_into_word .proc
; -- multiply 2 bytes A and Y, result as word in A/Y (unsigned)
sta P8ZP_SCRATCH_B1
sty P8ZP_SCRATCH_REG
lda #0
ldx #8
lsr P8ZP_SCRATCH_B1
- bcc +
clc
adc P8ZP_SCRATCH_REG
+ ror a
ror P8ZP_SCRATCH_B1
dex
bne -
tay
lda P8ZP_SCRATCH_B1
rts
sty _multiplicand
lsr a
sta _multiplier
lda #0
ldx #2
-
bcc +
clc
adc _multiplicand
+
ror a
ror _multiplier
bcc +
clc
adc _multiplicand
+
ror a
ror _multiplier
bcc +
clc
adc _multiplicand
+
ror a
ror _multiplier
bcc +
clc
adc _multiplicand
+
ror a
ror _multiplier
dex
bne -
; tay ; if you want 16 bits result in AY, enable this again
lda _multiplier
rts
.pend