mirror of
https://github.com/cc65/cc65.git
synced 2024-12-25 02:29:52 +00:00
61 lines
1.5 KiB
ArmAsm
61 lines
1.5 KiB
ArmAsm
;
|
|
; Ullrich von Bassewitz, 2004-06-30
|
|
;
|
|
; CC65 runtime: right shift support for ints
|
|
;
|
|
; 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 tosasrax
|
|
.import popax
|
|
.importzp tmp1
|
|
|
|
tosasrax:
|
|
and #$0F ; Bring the shift count into a valid range
|
|
sta tmp1 ; Save it
|
|
|
|
jsr popax ; Get the left hand operand
|
|
|
|
ldy tmp1 ; Get shift count
|
|
beq L9 ; Bail out if shift count zero
|
|
|
|
cpy #8 ; Shift count 8 or greater?
|
|
bcc L1 ; Jump if not
|
|
|
|
; Shift count is greater 8. The carry is set when we enter here.
|
|
|
|
tya
|
|
sbc #8
|
|
tay ; Adjust shift count
|
|
txa
|
|
ldx #$00 ; Shift by 8 bits
|
|
cmp #$00 ; Test sign bit
|
|
bpl L1
|
|
dex ; Make X the correct sign extended value
|
|
|
|
; Save the high byte so we can shift it
|
|
|
|
L1: stx tmp1 ; Save high byte
|
|
jmp L3
|
|
|
|
; Do the actual shift
|
|
|
|
L2: cpx #$80 ; Copy bit 15 into the carry
|
|
ror tmp1
|
|
ror a
|
|
L3: dey
|
|
bpl L2
|
|
|
|
; Done with shift
|
|
|
|
ldx tmp1
|
|
L9: rts
|
|
|
|
|
|
|