1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
|
;
; Ullrich von Bassewitz, 1998-08-05, 2004-06-25
;
; CC65 runtime: left shift support for ints and 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 tosaslax, tosshlax, aslaxy, shlaxy
.import popax
.importzp tmp1
.macpack cpu
tosshlax:
tosaslax:
sta tmp1 ; Save shift count
jsr popax ; Get the left hand operand
ldy tmp1 ; Get shift count
; Run into shlaxy
shlaxy:
aslaxy:
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 ; Get low byte
L1: asl a
dey
bne L1
tax
tya ; A = 0
rts
; Shift count is zero
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 L5
; Done with shift
ldx tmp1
L9: rts
|
