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38 lines
978 B
ArmAsm
38 lines
978 B
ArmAsm
;
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; Ullrich von Bassewitz, 07.08.1998
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; CC65 runtime: modulo operation for signed ints
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;
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; When negating values, we will ignore the possibility here, that one of the
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; values if $8000, in which case the negate will fail.
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.export tosmoda0, tosmodax
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.import popsargs, udiv16, negax
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.importzp ptr1, tmp1
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tosmoda0:
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ldx #0
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tosmodax:
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jsr popsargs ; Get arguments from stack, adjust sign
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jsr udiv16 ; Do the division
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lda ptr1 ; Load low byte of result
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ldx ptr1+1 ; Load high byte of result
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; Adjust the sign of the result. tmp1 contains the high byte of the left
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; operand, tmp2 contains the high byte of the right operand. The sign of
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; the result of the modulo operation is the same as that of the left
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; operand
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bit tmp1
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bpl Pos ; Jump if sign of result positive
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; Result is negative
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jmp negax ; Adjust the sign
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; Result is positive
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Pos: rts
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