mirror of
https://github.com/cc65/cc65.git
synced 2024-12-26 08:32:00 +00:00
c6db670be5
the stack. git-svn-id: svn://svn.cc65.org/cc65/trunk@5761 b7a2c559-68d2-44c3-8de9-860c34a00d81
76 lines
1.8 KiB
ArmAsm
76 lines
1.8 KiB
ArmAsm
;
|
|
; Ullrich von Bassewitz, 2004-06-30
|
|
;
|
|
; CC65 runtime: right shift support for unsigneds
|
|
;
|
|
; 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 tosshrax, shraxy
|
|
.import popax
|
|
.importzp tmp1
|
|
|
|
tosshrax:
|
|
sta tmp1 ; Save shift count
|
|
jsr popax ; Get the left hand operand
|
|
ldy tmp1 ; Get shift count
|
|
|
|
; Run into shraxy
|
|
|
|
shraxy:
|
|
pha
|
|
tya
|
|
and #$0F
|
|
beq L2 ; Nothing to shift
|
|
sec
|
|
sbc #8 ; Shift count 8 or greater?
|
|
beq L3 ; Jump if exactly 8
|
|
bcc L4 ; Jump if less than 8
|
|
|
|
; Shift count is greater than 8.
|
|
|
|
tay ; Shift count into Y
|
|
pla ; Discard low byte
|
|
txa ; Get high byte
|
|
|
|
L1: lsr a
|
|
dey
|
|
bne L1
|
|
ldx #$00 ; High byte is zero
|
|
rts
|
|
|
|
; Shift count is zero
|
|
|
|
L2: pla
|
|
rts
|
|
|
|
; Shift count is exactly 8
|
|
|
|
L3: pla ; Drop low byte from stack ...
|
|
txa ; Move high byte to low
|
|
ldx #$00 ; Clear high byte
|
|
rts
|
|
|
|
; Shift count is less than 8
|
|
|
|
L4: adc #8 ; Correct counter
|
|
tay ; Shift count into Y
|
|
pla ; Restore low byte
|
|
stx tmp1 ; Save high byte of lhs
|
|
L5: lsr tmp1
|
|
ror a
|
|
dey
|
|
bne L5
|
|
|
|
; Done with shift
|
|
|
|
ldx tmp1
|
|
rts
|
|
|
|
|