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which included commits to RCS files with non-trunk default branches. git-svn-id: svn://svn.cc65.org/cc65/trunk@3 b7a2c559-68d2-44c3-8de9-860c34a00d81
186 lines
3.0 KiB
ArmAsm
186 lines
3.0 KiB
ArmAsm
;
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; Ullrich von Bassewitz, 20.09.1998
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; CC65 runtime: right shift support for longs
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;
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.export tosasreax, tosshreax
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.import addysp1
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.importzp sp, sreg, ptr1, ptr2
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; --------------------------------------------------------------------
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; signed shift
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.proc tosasreax
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jsr getlhs ; Get the lhs from the stack
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jsr checkovf ; Check for overflow
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bcs L6 ; Jump if shift count too large
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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 ptr1+1
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stx ptr1
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ldx ptr2
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stx ptr1+1
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ldy #0
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ldx ptr2+1
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stx ptr2
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bpl L2
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dey ; Get sign
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L2: sty ptr2+1
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jmp 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 ptr2+1 ; 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: cmp #$80 ; Get sign bit into C
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ror a
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ror ptr2
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ror ptr1+1
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ror ptr1
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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: sta sreg+1
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lda ptr2
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sta sreg
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ldx ptr1+1
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lda ptr1
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L5: rts
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; Jump here if shift count overflow
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L6: ldx #0
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lda ptr2+1 ; Check sign
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bpl L7
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dex
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L7: stx sreg+1
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stx sreg
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txa
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rts
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.endproc
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; --------------------------------------------------------------------
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; unsigned shift
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.proc tosshreax
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jsr getlhs ; Get the lhs from the stack
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jsr checkovf ; Check for overflow
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bcs L6 ; Jump if shift count too large
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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 ptr1+1
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stx ptr1
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ldx ptr2
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stx ptr1+1
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ldx ptr2+1
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stx ptr2
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ldx #0
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stx ptr2+1
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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 ptr2+1 ; 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: lsr a
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ror ptr2
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ror ptr1+1
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ror ptr1
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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: sta sreg+1
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lda ptr2
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sta sreg
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ldx ptr1+1
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lda ptr1
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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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.endproc
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; --------------------------------------------------------------------
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; Helpers
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.proc getlhs ; 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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jmp addysp1
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.endproc
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.proc checkovf ; Check for shift overflow
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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 TooLarge ; Shift count too large
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cpy #32
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bcc Ok
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TooLarge:
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sec
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Ok: rts
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.endproc
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