1
0
mirror of https://github.com/cc65/cc65.git synced 2024-10-30 12:28:25 +00:00
cc65/libsrc/runtime/lshr.s
cuz c122f18605 New code for the shift functions
git-svn-id: svn://svn.cc65.org/cc65/trunk@3143 b7a2c559-68d2-44c3-8de9-860c34a00d81
2004-07-05 22:24:06 +00:00

49 lines
1.0 KiB
ArmAsm

;
; 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