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64 lines
1.2 KiB
ArmAsm
64 lines
1.2 KiB
ArmAsm
;
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; Ullrich von Bassewitz, 2009-11-05
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; Helper function for graphics functions: Multiply two values, one being
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; an 8.8 fixed point one, and return the rounded and scaled result.
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;
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; The module has two entry points: One is C callable and expects the
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; parameters in ax and the stack, the second is assembler callable and
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; expects the parameters in ax and ptr1
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;
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.export _tgi_imulround, tgi_imulround
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.import popax, imul16x16r32
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.include "zeropage.inc"
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;----------------------------------------------------------------------------
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;
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.code
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; C callable entry point
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_tgi_imulround:
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; Get arguments
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sta ptr1
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stx ptr1+1 ; Save lhs
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jsr popax ; Get rhs
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; ASM callable entry point
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tgi_imulround:
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; Multiplicate
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jsr imul16x16r32
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; Round the result
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cmp #$80 ; Frac(x) >= 0.5?
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txa
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ldy sreg+1 ; Check sign
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bmi @L1
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adc #$00
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tay
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lda sreg
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adc #$00
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tax
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tya
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rts
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@L1: sbc #$00
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tay
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lda sreg
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sbc #$00
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tax
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tya
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rts
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