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36 lines
904 B
ArmAsm
36 lines
904 B
ArmAsm
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; Ullrich von Bassewitz, 2010-11-02
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; CC65 runtime: 8x8 => 16 multiplication
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.export umul8x8r16
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.export mul8x8r16 := umul8x8r16
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.importzp ptr1, ptr3
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;---------------------------------------------------------------------------
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; 8x8 => 16 multiplication routine.
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;
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; lhs rhs result result also in
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; -------------------------------------------------------------
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; ptr1-lo ptr3-lo ax ptr1
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;
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umul8x8r16:
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lda #0 ; Clear byte 1
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ldy #8 ; Number of bits
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lsr ptr1 ; Get first bit of lhs into carry
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@L0: bcc @L1
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clc
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adc ptr3
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@L1: ror
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ror ptr1
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dey
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bne @L0
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tax
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stx ptr1+1 ; Result in a/x and ptr1
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lda ptr1 ; Load the result
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rts ; Done
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