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44 lines
782 B
ArmAsm
44 lines
782 B
ArmAsm
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; Ullrich von Bassewitz, 07.08.1998
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; CC65 runtime: multiplication for ints
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.export tosumula0, tosumulax, tosmula0, tosmulax
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.import popsreg
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.importzp sreg, tmp1, ptr4
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tosmula0:
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tosumula0:
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ldx #0
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tosmulax:
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tosumulax:
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mul16: sta ptr4
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stx ptr4+1 ; Save right operand
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jsr popsreg ; Get left operand
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; Do ptr4*sreg --> AX (see mult-div.s from "The Fridge").
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lda #0
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sta tmp1
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ldx sreg+1 ; Get into register for speed
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ldy #16 ; Number of bits
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L0: lsr tmp1
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ror a
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ror ptr4+1
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ror ptr4
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bcc L1
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clc
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adc sreg
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pha
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txa ; hi byte of left op
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adc tmp1
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sta tmp1
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pla
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L1: dey
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bpl L0
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lda ptr4 ; Load the result
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ldx ptr4+1
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rts ; Done
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