6502/cc65
1
0
Fork 0
mirror of https://github.com/cc65/cc65.git synced 2024-12-23 19:29:37 +00:00
Code Issues Projects Releases Wiki Activity

Add another entry point to the shift left routine, that shifts A/X by Y

Browse Source 
without going over the stack.


git-svn-id: svn://svn.cc65.org/cc65/trunk@5742 b7a2c559-68d2-44c3-8de9-860c34a00d81
This commit is contained in:
uz 2012-06-24 22:04:00 +00:00
parent e3fb0233c8
commit b9ffe5de13
1 changed files with 49 additions and 24 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

73
libsrc/runtime/shl.s
View File

@ -11,45 +11,70 @@
;
.export tosaslax, tosshlax
.import popax
.importzp tmp1
.export tosaslax, tosshlax, aslaxy, shlaxy
.import popax
.importzp tmp1
.macpack cpu
tosshlax:
tosaslax:
and #$0F ; Bring the shift count into a valid range
sta tmp1 ; Save it
sta tmp1 ; Save shift count 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 L3 ; Jump if not
; Run into shlaxy
; Shift count is greater 7. The carry is set when we enter here.
tax
shlaxy:
aslaxy:
pha
tya
sbc #8
tay
txa
jmp L2
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 ; Get low byte
L1: asl a
L2: dey
bpl L1
dey
bne L1
tax
lda #$00
tya ; A = 0
rts
; Shift count is less than 8.
; Shift count is zero
L3: stx tmp1 ; Save high byte of lhs
L4: asl a
L2: pla
rts
; Shift count is exactly 8
.if (.cpu .bitand CPU_ISET_65SC02)
L3: plx ; Low byte from stack into X
rts ; A is already zero
.else
L3: pla ; Low byte from stack ...
tax ; ... into X
lda #$00 ; Clear low byte
rts
.endif
; 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: asl a
rol tmp1
dey
bne L4
bne L5
; Done with shift