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99 lines
1.7 KiB
ArmAsm
99 lines
1.7 KiB
ArmAsm
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; Ullrich von Bassewitz, 17.08.1998
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; CC65 runtime: division for long unsigned ints
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;
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.export tosudiv0ax, tosudiveax, getlop, udiv32
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.import addysp1
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.importzp sp, sreg, tmp3, tmp4, ptr1, ptr2, ptr3, ptr4
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tosudiv0ax:
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ldy #$00
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sty sreg
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sty sreg+1
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tosudiveax:
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jsr getlop ; Get the paramameters
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jsr udiv32 ; Do the division
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lda ptr1 ; Result is in ptr1:sreg
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ldx ptr1+1
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rts
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; Pop the parameters for the long division and put it into the relevant
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; memory cells. Called from the signed divisions also.
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getlop: sta ptr3 ; Put right operand in place
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stx ptr3+1
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lda sreg
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sta ptr4
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lda sreg+1
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sta ptr4+1
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ldy #0 ; Put left operand in place
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lda (sp),y
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sta ptr1
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iny
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lda (sp),y
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sta ptr1+1
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iny
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lda (sp),y
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sta sreg
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iny
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lda (sp),y
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sta sreg+1
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jmp addysp1 ; Drop parameters
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; Do (ptr1:sreg) / (ptr3:ptr4) --> (ptr1:sreg), remainder in (ptr2:tmp3:tmp4)
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; This is also the entry point for the signed division
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udiv32: lda #0
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sta ptr2+1
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sta tmp3
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sta tmp4
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; sta ptr1+1
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ldy #32
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L0: asl ptr1
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rol ptr1+1
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rol sreg
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rol sreg+1
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rol a
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rol ptr2+1
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rol tmp3
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rol tmp4
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; Do a subtraction. we do not have enough space to store the intermediate
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; result, so we may have to do the subtraction twice.
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pha
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cmp ptr3
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lda ptr2+1
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sbc ptr3+1
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lda tmp3
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sbc ptr4
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lda tmp4
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sbc ptr4+1
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bcc L1
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; Overflow, do the subtraction again, this time store the result
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sta tmp4 ; We have the high byte already
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pla
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sbc ptr3 ; byte 0
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pha
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lda ptr2+1
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sbc ptr3+1
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sta ptr2+1 ; byte 1
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lda tmp3
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sbc ptr4
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sta tmp3 ; byte 2
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inc ptr1 ; Set result bit
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L1: pla
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dey
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bne L0
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sta ptr2
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rts
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