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87 lines
1.3 KiB
ArmAsm
87 lines
1.3 KiB
ArmAsm
;
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; Ullrich von Bassewitz, 07.08.1998
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;
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; CC65 runtime: division for unsigned ints
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;
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.export tosudiva0, tosudivax, udiv16
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.import popsreg
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.importzp sreg, ptr1, ptr4
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tosudiva0:
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ldx #$00 ; Clear high byte
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tosudivax:
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sta ptr4
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stx ptr4+1 ; Save right operand
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jsr popsreg ; Get left operand
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; Do the division
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jsr udiv16
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; Result is in sreg, remainder in ptr1
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lda sreg
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ldx sreg+1
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rts
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;---------------------------------------------------------------------------
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; 16by16 division. Divide sreg by ptr4. Result is in sreg, remainder in ptr1
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; (see mult-div.s from "The Fridge").
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; This is also the entry point for the signed division
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udiv16: lda #0
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sta ptr1+1
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ldy #16
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ldx sreg+1
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beq udiv16by8a
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L0: asl sreg
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rol sreg+1
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rol a
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rol ptr1+1
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pha
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cmp ptr4
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lda ptr1+1
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sbc ptr4+1
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bcc L1
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sta ptr1+1
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pla
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sbc ptr4
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pha
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inc sreg
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L1: pla
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dey
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bne L0
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sta ptr1
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rts
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;---------------------------------------------------------------------------
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; 16by8 division
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udiv16by8:
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lda #0
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sta ptr1+1
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ldy #16
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udiv16by8a:
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@L0: asl sreg
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rol sreg+1
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rol a
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bcs @L1
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cmp ptr4
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bcc @L2
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@L1: sbc ptr4
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inc sreg
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@L2: dey
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bne @L0
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sta ptr1
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rts
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