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Go64!
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Go64_1999-12_1999_CSW_Side_A.d64
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usrmod.asm
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Assembly Source File
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2023-02-26
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1KB
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59 lines
; Modulo function using USR()
; Copyright 1992,1999 Peter Karlsson
; For Go64!/Commodore World magazine
*= 49152
; BASIC ROM entry points used
usrvec = $0311
mov2f57 = $bbca
mov2f5c = $bbc7
frmnum = $ad8a
fdivmem = $bb0f
int = $bccc
fmultmem = $ba28
fsubmem = $b850
tmp1 = $57
tmp2 = $5c
; Setup the USR vector
lda #<modulo
ldx #>modulo
sta usrvec
stx usrvec+1
rts
; Entry point for the USR function
modulo ; Move numerator (FAC1) to TMP1
jsr mov2f57
; Retrieve denominator and
; move from FAC1 to TMP2
jsr frmnum
jsr mov2f5c
; Calculate FAC1=FAC1/TMP1
; retval=x/y
lda #<tmp1
ldy #>tmp1
jsr fdivmem
; Calculate FAC1=INT(FAC1)
; retval=int(x/y)
jsr int
; Calculate FAC1=FAC1*TMP2
; retval=int(x/y)*y
lda #<tmp2
ldy #>tmp2
jsr fmultmem
; Calculate FAC1=TMP1-FAC1
; retval=x-int(x/y)*y
; =mod(x,y)
lda #<tmp1
lda #>tmp1
jmp fsubmem