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mult58.a
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mult58.a
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; mult58.a
; from codebase64, by litwr: https://www.codebase64.org/doku.php?id=base:another_fast_8bit_multiplication
; TobyLobster combined 8 bit results to make a 16 bit multiply, see mult16 for 8 bit version
;
; 16 bit x 16 bit unsigned multiply, 32 bit result
; Average cycles: 365.03
; 772 bytes
inputA = $02 ; 2 bytes (a0,a1)
inputB = $04 ; 2 bytes (b0,b1)
result = $06 ; 4 bytes
min = $0a
result_low = $0b
* = $0200
; align tables to page for speed
sqrlo
!for i, 0, 255 {
!byte <(i*i)
}
sqrhi
!for i, 0, 255 {
!byte >(i*i)
}
; ***************************************************************************************
; 16 bit x 16 bit unsigned multiply, 32 bit result
;
; On Entry:
; inputA: multiplier (2 bytes)
; inputB: multiplicand (2 bytes)
;
; On Exit:
; result: product (4 bytes)
mult
; (a0*b0) 8 bit multiply
ldx inputB ; 3
lda inputA ; 3
sta min ; 3
sec ; 2
sbc inputB ; 3
bcc + ; 2/3
; inputA >= inputB
stx min ; 3
ldx inputA ; 3
bcs ++ ; 3 ALWAYS branch
+
; inputA < inputB
sbc #0 ; 2 also sets carry
eor #255 ; 2
++
tay
lda sqrlo,x
sbc sqrlo,y
sta result
lda sqrhi,x
sbc sqrhi,y
tay
clc
ldx min
lda result
adc sqrlo,x
sta result
tya
adc sqrhi,x
ror
sta result+1 ; x is high byte
ror result
; (a1*b0) 8 bit multiply
ldx inputB ; 3
lda inputA+1 ; 3
sta min ; 3
sec ; 2
sbc inputB ; 3
bcc + ; 2/3
; inputA >= inputB
stx min ; 3
ldx inputA+1 ; 3
bcs ++ ; 3 ALWAYS branch
+
; inputA < inputB
sbc #0 ; 2 also sets carry
eor #255 ; 2
++
tay
lda sqrlo,x
sbc sqrlo,y
sta result_low
lda sqrhi,x
sbc sqrhi,y
tay
clc
ldx min
lda result_low
adc sqrlo,x
sta result_low
tya
adc sqrhi,x
ror
tax
lda result_low
ror
clc ;
adc result+1 ;
sta result+1 ;
txa ;
adc #0 ;
sta result+2 ;
; (a0*b1) 8 bit multiply
ldx inputB+1 ; 3
lda inputA ; 3
sta min ; 3
sec ; 2
sbc inputB+1 ; 3
bcc + ; 2/3
; inputA >= inputB
stx min ; 3
ldx inputA ; 3
bcs ++ ; 3 ALWAYS branch
+
; inputA < inputB
sbc #0 ; 2 also sets carry
eor #255 ; 2
++
tay
lda sqrlo,x
sbc sqrlo,y
sta result_low
lda sqrhi,x
sbc sqrhi,y
tay
clc
ldx min
lda result_low
adc sqrlo,x
sta result_low
tya
adc sqrhi,x
ror
tax
lda result_low
ror
clc ;
adc result+1 ;
sta result+1 ;
txa ;
adc result+2 ;
sta result+2 ;
lda #0 ;
rol ; remember the carry for result+3
sta result+3 ;
; (a1*b1) 8 bit multiply
ldx inputB+1 ; 3
lda inputA+1 ; 3
sta min ; 3
sec ; 2
sbc inputB+1 ; 3
bcc + ; 2/3
; inputA >= inputB
stx min ; 3
ldx inputA+1 ; 3
bcs ++ ; 3 ALWAYS branch
+
; inputA < inputB
sbc #0 ; 2 also sets carry
eor #255 ; 2
++
tay
lda sqrlo,x
sbc sqrlo,y
sta result_low
lda sqrhi,x
sbc sqrhi,y
tay
clc
ldx min
lda result_low
adc sqrlo,x
sta result_low
tya
adc sqrhi,x
ror
tax
lda result_low
ror
clc ;
adc result+2 ;
sta result+2 ;
txa ;
adc result+3 ;
sta result+3 ;
rts ;