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70 lines
1.0 KiB
ArmAsm
70 lines
1.0 KiB
ArmAsm
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; Ullrich von Bassewitz, 05.08.1998
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;
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; CC65 runtime: left shift support for ints
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;
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.export tosasla0, tosaslax, tosshla0, tosshlax
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.import popsreg, return0
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.importzp sreg
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tosshla0:
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tosasla0:
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ldx #0
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tosshlax:
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tosaslax:
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jsr popsreg ; get TOS into sreg
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cpx #0
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bne TooLarge
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cmp #16
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bcs TooLarge
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cmp #8 ; Shift count greater 8?
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beq L3 ; Jump if exactly 8
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bcc L1 ; Jump if no
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; Shift count is greater 8. Do the first 8 bits the fast way
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ldy sreg
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sty sreg+1
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stx sreg ; Low byte = 0
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sec
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sbc #8
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; Shift count less than 8 if we come here
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L1: tay ; Shift count --> Y
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beq Zero ; Done if shift count zero
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lda sreg ; get low byte for faster shift
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; Do the actual shift
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L2: asl a
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rol sreg+1
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dey
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bne L2
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; Done with shift
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ldx sreg+1
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rts
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; Shift count == 8
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L3: txa ; X == 0, now A == 0
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ldx sreg
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rts
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; Shift count was zero
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Zero: lda sreg
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ldx sreg+1
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rts
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; Shift count too large, result is zero
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TooLarge:
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jmp return0
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