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96 lines
1.5 KiB
ArmAsm
96 lines
1.5 KiB
ArmAsm
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; Ullrich von Bassewitz, 20.09.1998
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;
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; CC65 runtime: left shift support for longs
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;
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.export tosasleax, tosshleax
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.import addysp1
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.importzp sp, sreg, ptr1, ptr2
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tosshleax:
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tosasleax:
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; Get the lhs from stack into ptr1/ptr2
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pha
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ldy #0
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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 ptr2
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iny
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lda (sp),y
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sta ptr2+1
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pla
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jsr addysp1
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; Check for shift overflow or zero shift
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tay ; Low byte of shift count into y
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txa ; Get byte 2
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ora sreg
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ora sreg+1 ; Check high 24 bit
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bne @L6 ; Shift count too large
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cpy #32
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bcs @L6
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cpy #0 ; Shift count zero?
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beq @L5
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; We must shift. Shift by multiples of eight if possible
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tya
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@L1: cmp #8
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bcc @L3
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sbc #8
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ldx ptr2
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stx ptr2+1
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ldx ptr1+1
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stx ptr2
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ldx ptr1
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stx ptr1+1
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ldx #0
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stx ptr1
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beq @L1
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; Shift count is now less than eight. Do a real shift.
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@L3: tay ; Shift count to Y
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lda ptr1 ; Get one byte into A for speed
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cpy #0
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beq @L4a ; Jump if done
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@L4: asl a
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rol ptr1+1
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rol ptr2
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rol ptr2+1
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dey
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bne @L4
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; Put the result in place
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@L4a: ldx ptr2
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stx sreg
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ldx ptr2+1
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stx sreg+1
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ldx ptr1+1
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@L5: rts
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; Jump here if shift count overflow
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@L6: lda #0
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sta sreg+1
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sta sreg
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tax
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rts
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