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
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
|
/* Copyright (C) 1996-2013 Free Software Foundation, Inc.
Contributed by Richard Henderson (rth@tamu.edu)
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library. If not, see
<http://www.gnu.org/licenses/>. */
/* Bytewise compare two null-terminated strings. */
#include <sysdep.h>
.set noat
.set noreorder
.text
ENTRY(strcmp)
#ifdef PROF
ldgp gp, 0(pv)
lda AT, _mcount
jmp AT, (AT), _mcount
.prologue 1
#else
.prologue 0
#endif
ldq_u t0, 0(a0) # e0 : give cache time to catch up
xor a0, a1, t2 # .. e1 : are s1 and s2 co-aligned?
ldq_u t1, 0(a1) # e0 :
and t2, 7, t2 # .. e1 :
lda t3, -1 # e0 :
bne t2, $unaligned # .. e1 :
/* On entry to this basic block:
t0 == the first destination word for masking back in
t1 == the first source word.
t3 == -1. */
$aligned:
mskqh t3, a0, t3 # e0 :
nop # .. e1 :
ornot t1, t3, t1 # e0 :
ornot t0, t3, t0 # .. e1 :
cmpbge zero, t1, t7 # e0 : bits set iff null found
bne t7, $eos # e1 (zdb)
/* Aligned compare main loop.
On entry to this basic block:
t0 == an s1 word.
t1 == an s2 word not containing a null. */
$a_loop:
xor t0, t1, t2 # e0 :
bne t2, $wordcmp # .. e1 (zdb)
ldq_u t1, 8(a1) # e0 :
ldq_u t0, 8(a0) # .. e1 :
addq a1, 8, a1 # e0 :
addq a0, 8, a0 # .. e1 :
cmpbge zero, t1, t7 # e0 :
beq t7, $a_loop # .. e1 (zdb)
br $eos # e1 :
/* The two strings are not co-aligned. Align s1 and cope. */
$unaligned:
and a0, 7, t4 # e0 : find s1 misalignment
and a1, 7, t5 # .. e1 : find s2 misalignment
subq a1, t4, a1 # e0 :
/* If s2 misalignment is larger than s2 misalignment, we need
extra startup checks to avoid SEGV. */
cmplt t4, t5, t8 # .. e1 :
beq t8, $u_head # e1 :
mskqh t3, t5, t3 # e0 :
ornot t1, t3, t3 # e0 :
cmpbge zero, t3, t7 # e1 : is there a zero?
beq t7, $u_head # e1 :
/* We've found a zero in the first partial word of s2. Align
our current s1 and s2 words and compare what we've got. */
extql t1, t5, t1 # e0 :
extql t0, a0, t0 # e0 :
cmpbge zero, t1, t7 # .. e1 : find that zero again
br $eos # e1 : and finish up
.align 3
$u_head:
/* We know just enough now to be able to assemble the first
full word of s2. We can still find a zero at the end of it.
On entry to this basic block:
t0 == first word of s1
t1 == first partial word of s2. */
ldq_u t2, 8(a1) # e0 : load second partial s2 word
lda t3, -1 # .. e1 : create leading garbage mask
extql t1, a1, t1 # e0 : create first s2 word
mskqh t3, a0, t3 # e0 :
extqh t2, a1, t4 # e0 :
ornot t0, t3, t0 # .. e1 : kill s1 garbage
or t1, t4, t1 # e0 : s2 word now complete
cmpbge zero, t0, t7 # .. e1 : find zero in first s1 word
ornot t1, t3, t1 # e0 : kill s2 garbage
lda t3, -1 # .. e1 :
mskql t3, a1, t3 # e0 : mask for s2[1] bits we have seen
bne t7, $eos # .. e1 :
xor t0, t1, t4 # e0 : compare aligned words
bne t4, $wordcmp # .. e1 (zdb)
or t2, t3, t3 # e0 :
cmpbge zero, t3, t7 # e1 :
bne t7, $u_final # e1 :
/* Unaligned copy main loop. In order to avoid reading too much,
the loop is structured to detect zeros in aligned words from s2.
This has, unfortunately, effectively pulled half of a loop
iteration out into the head and half into the tail, but it does
prevent nastiness from accumulating in the very thing we want
to run as fast as possible.
On entry to this basic block:
t2 == the unshifted low-bits from the next s2 word. */
.align 3
$u_loop:
extql t2, a1, t3 # e0 :
ldq_u t2, 16(a1) # .. e1 : load next s2 high bits
ldq_u t0, 8(a0) # e0 : load next s1 word
addq a1, 8, a1 # .. e1 :
addq a0, 8, a0 # e0 :
nop # .. e1 :
extqh t2, a1, t1 # e0 :
cmpbge zero, t0, t7 # .. e1 : find zero in current s1 word
or t1, t3, t1 # e0 :
bne t7, $eos # .. e1 :
xor t0, t1, t4 # e0 : compare the words
bne t4, $wordcmp # .. e1 (zdb)
cmpbge zero, t2, t4 # e0 : find zero in next low bits
beq t4, $u_loop # .. e1 (zdb)
/* We've found a zero in the low bits of the last s2 word. Get
the next s1 word and align them. */
$u_final:
ldq_u t0, 8(a0) # e1 :
extql t2, a1, t1 # .. e0 :
cmpbge zero, t1, t7 # e0 :
/* We've found a zero somewhere in a word we just read.
On entry to this basic block:
t0 == s1 word
t1 == s2 word
t7 == cmpbge mask containing the zero. */
.align 3
$eos:
negq t7, t6 # e0 : create bytemask of valid data
and t6, t7, t8 # e1 :
subq t8, 1, t6 # e0 :
or t6, t8, t7 # e1 :
zapnot t0, t7, t0 # e0 : kill the garbage
zapnot t1, t7, t1 # .. e1 :
xor t0, t1, v0 # e0 : and compare
beq v0, $done # .. e1 :
/* Here we have two differing co-aligned words in t0 & t1.
Bytewise compare them and return (t0 > t1 ? 1 : -1). */
$wordcmp:
cmpbge t0, t1, t2 # e0 : comparison yields bit mask of ge
cmpbge t1, t0, t3 # .. e1 :
xor t2, t3, t0 # e0 : bits set iff t0/t1 bytes differ
negq t0, t1 # e1 : clear all but least bit
and t0, t1, t0 # e0 :
lda v0, -1 # .. e1 :
and t0, t2, t1 # e0 : was bit set in t0 > t1?
cmovne t1, 1, v0 # .. e1 (zdb)
$done:
ret # e1 :
END(strcmp)
libc_hidden_builtin_def (strcmp)
|
