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64 lines
1.6 KiB
ArmAsm
64 lines
1.6 KiB
ArmAsm
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; Ullrich von Bassewitz, 2009-08-17
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; CC65 runtime: multiplication for ints. Short versions.
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.export tosumula0, tosmula0
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.export mul8x16, mul8x16a
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.import popptr1
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.importzp ptr1, ptr4
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;---------------------------------------------------------------------------
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; 8x16 routine with external entry points used by the 16x16 routine in mul.s
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tosmula0:
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tosumula0:
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sta ptr4
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mul8x16:jsr popptr1 ; Get left operand (Y=0 by popptr1)
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tya ; Clear byte 1
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ldy #8 ; Number of bits
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ldx ptr1+1 ; check if lhs is 8 bit only
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beq mul8x8 ; Do 8x8 multiplication if high byte zero
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mul8x16a:
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sta ptr4+1 ; Clear byte 2
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lsr ptr4 ; Get first bit into carry
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@L0: bcc @L1
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clc
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adc ptr1
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tax
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lda ptr1+1 ; hi byte of left op
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adc ptr4+1
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sta ptr4+1
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txa
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@L1: ror ptr4+1
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ror a
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ror ptr4
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dey
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bne @L0
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tax
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lda ptr4 ; Load the result
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rts
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;---------------------------------------------------------------------------
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; 8x8 multiplication routine
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mul8x8:
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lsr ptr4 ; Get first bit into carry
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@L0: bcc @L1
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clc
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adc ptr1
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@L1: ror
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ror ptr4
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dey
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bne @L0
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tax
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lda ptr4 ; Load the result
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rts ; Done
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