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faster MUL for small numbers

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This commit is contained in:
David Schmenk 2023-12-16 09:39:31 -08:00
parent 097bde5257
commit 3ddb448775
1 changed files with 56 additions and 2 deletions
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58
src/vmsrc/apple/plvm802.s
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@ -577,17 +577,71 @@ IDXW PLA
;*
MUL LDX #$10
LDA NOS,S
EOR #$FFFF
CMP TOS,S
BCS _MULSWP
- ASL ; SKIP LEADING ZEROS
BCS +
DEX
BNE -
BEQ _MULEX
+ EOR #$FFFF
STA TMP
LDA #$0000
LDA TOS,S
DEX
BEQ _MULEX
_MULLP ASL
ASL TMP ; MULTPLR
BCS +
ADC TOS,S ; MULTPLD
+ DEX
BNE _MULLP
_MULEX STA NOS,S ; PROD
JMP DROP
_MULSWP LDA TOS,S
- ASL ; SKIP LEADING ZEROS
BCS +
DEX
BNE -
BEQ _MULEX
+ EOR #$FFFF
STA TMP
LDA NOS,S
DEX
BEQ _MULEX
_MULSLP ASL
ASL TMP ; MULTPLR
BCS +
ADC NOS,S ; MULTPLD
+ DEX
BNE _MULSLP
STA NOS,S ; PROD
JMP DROP
;
;MUL LDX #$04
; LDA NOS,S
; EOR #$FFFF
; STA TMP
; LDA #$0000
;_MULLP ASL
; ASL TMP ; MULTPLR
; BCS +
; ADC TOS,S ; MULTPLD
;+ ASL
; ASL TMP ; MULTPLR
; BCS +
; ADC TOS,S ; MULTPLD
;+ ASL
; ASL TMP ; MULTPLR
; BCS +
; ADC TOS,S ; MULTPLD
;+ ASL
; ASL TMP ; MULTPLR
; BCS +
; ADC TOS,S ; MULTPLD
;+ DEX
; BNE _MULLP
; STA NOS,S ; PROD
; JMP DROP
;*
;* INTERNAL DIVIDE ALGORITHM
;*