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64 lines
1.6 KiB
ArmAsm
64 lines
1.6 KiB
ArmAsm
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; Ullrich von Bassewitz, 2011-07-10
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; CC65 runtime: 8x16 => 24 unsigned multiplication
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.export umul8x16r24, umul8x16r24m
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.export umul8x16r16, umul8x16r16m
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.include "zeropage.inc"
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;---------------------------------------------------------------------------
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; 8x16 => 24 unsigned multiplication routine. Because the overhead for a
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; 8x16 => 16 unsigned multiplication routine is small, we will tag it with
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; the matching labels as well.
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;
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; routine lhs rhs result result also in
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; -----------------------------------------------------------------------
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; umul8x16r24 ptr1-lo ax ax:sreg-lo ptr1:sreg-lo
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; umul8x16r24m ptr1-lo ptr3 ax:sreg-lo ptr1:sreg-lo
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;
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; ptr3 ist left intact by the routine.
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;
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umul8x16r24:
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umul8x16r16:
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sta ptr3
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stx ptr3+1
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umul8x16r24m:
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umul8x16r16m:
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ldx #0
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stx ptr1+1
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stx sreg
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ldy #8 ; Number of bits
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ldx ptr3 ; Get into register for speed
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lda ptr1
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ror a ; Get next bit into carry
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@L0: bcc @L1
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clc
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pha
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txa
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adc ptr1+1
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sta ptr1+1
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lda ptr3+1
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adc sreg
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sta sreg
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pla
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@L1: ror sreg
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ror ptr1+1
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ror a
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dey
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bne @L0
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sta ptr1 ; Save low byte of result
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ldx ptr1+1 ; Load high byte of result
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rts ; Done
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