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;
; Ullrich von Bassewitz, 2004-06-30
;
; CC65 runtime: right shift support for unsigned longs
;
; Note: The standard declares a shift count that is negative or >= the
; bitcount of the shifted type for undefined behaviour.
;
; Note^2: The compiler knowns about the register/zero page usage of this
; function, so you need to change the compiler source if you change it!
;
.export tosshreax
.import popeax
.importzp sreg, tmp1
tosshreax:
and #$1F ; Bring the shift count into a valid range
sta tmp1 ; Save it
jsr popeax ; Get the left hand operand
ldy tmp1 ; Get shift count
beq L9 ; Bail out if shift count zero
stx tmp1 ; Save byte 1
; Do the actual shift. Faster solutions are possible but need a lot more code.
L2: lsr sreg+1
ror sreg
ror tmp1
ror a
dey
bne L2
; Shift done
ldx tmp1
L9: rts
|
