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33 lines
1.0 KiB
ArmAsm
33 lines
1.0 KiB
ArmAsm
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; Christian Krueger, 24-May-2018
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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 is $8000, in which case the negate will fail.
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.export tosmoda0, tosmodax
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.import absvaludiv16, negax
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.importzp sp, sreg, tmp1
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tosmoda0:
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ldx #0
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tosmodax:
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; Prepare adjustment of the sign of the result. The sign of the result of the
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; modulo operation is the same as that of the left operand.
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pha
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ldy #1 ; Prepare lhs operant hi-byte fetch
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lda (sp),y
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sta tmp1 ; Save post negation indicator to tmp1
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pla ; Back to entry accu
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jsr absvaludiv16
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ldx sreg+1 ; Remainder to return registers
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lda sreg
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ldy tmp1 ; Fetch indicator
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bmi negate
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rts
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negate: jmp negax
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