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84 lines
2.0 KiB
ArmAsm
84 lines
2.0 KiB
ArmAsm
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; Ullrich von Bassewitz, 1998-08-05, 2004-06-25
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;
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; CC65 runtime: left shift support for ints and unsigneds
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;
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; Note: The standard declares a shift count that is negative or >= the
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; bitcount of the shifted type for undefined behaviour.
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;
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; Note^2: The compiler knowns about the register/zero page usage of this
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; function, so you need to change the compiler source if you change it!
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;
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.export tosaslax, tosshlax, aslaxy, shlaxy
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.import popax
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.importzp tmp1
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.macpack cpu
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tosshlax:
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tosaslax:
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sta tmp1 ; Save shift count
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jsr popax ; Get the left hand operand
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ldy tmp1 ; Get shift count
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; Run into shlaxy
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shlaxy:
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aslaxy:
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pha
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tya
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and #$0F
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beq L2 ; Nothing to shift
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sec
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sbc #8 ; Shift count 8 or greater?
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beq L3 ; Jump if exactly 8
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bcc L4 ; Jump if less than 8
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; Shift count is greater than 8.
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tay ; Shift count into Y
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pla ; Get low byte
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L1: asl a
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dey
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bne L1
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tax
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tya ; A = 0
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rts
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; Shift count is zero
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L2: pla
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rts
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; Shift count is exactly 8
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.if (.cpu .bitand CPU_ISET_65SC02)
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L3: plx ; Low byte from stack into X
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rts ; A is already zero
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.else
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L3: pla ; Low byte from stack ...
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tax ; ... into X
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lda #$00 ; Clear low byte
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rts
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.endif
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; Shift count is less than 8
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L4: adc #8 ; Correct counter
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tay ; Shift count into Y
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pla ; Restore low byte
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stx tmp1 ; Save high byte of lhs
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L5: asl a
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rol tmp1
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dey
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bne L5
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; Done with shift
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ldx tmp1
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L9: rts
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