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A description of positions [left, right] is appropriate more for C code than for Assembly code. (A description of timing [first argument, second argument] is more appropriate for the way that Assembly code is written.)
46 lines
1005 B
ArmAsm
46 lines
1005 B
ArmAsm
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; Ullrich von Bassewitz, 2010-11-03
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; CC65 runtime: 16x16 => 32 signed multiplication
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.export imul16x16r32
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.import negax, umul16x16r32m, negeax
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.include "zeropage.inc"
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;---------------------------------------------------------------------------
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; 16x16 => 32 signed multiplication routine.
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;
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; LHS RHS result result also in
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; -------------------------------------------------------------
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; ax ptr1 ax:sreg
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;
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; There is probably a faster way to do this.
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;
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imul16x16r32:
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stx tmp1
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cpx #0
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bpl @L1
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jsr negax
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@L1: sta ptr3
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stx ptr3+1
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lda ptr1+1
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eor tmp1
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sta tmp1
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lda ptr1
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ldx ptr1+1
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bpl @L2
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jsr negax
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sta ptr1
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stx ptr1+1
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@L2: jsr umul16x16r32m
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ldy tmp1
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bpl @L3
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jmp negeax
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@L3: rts
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