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
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
|
/* strcat(dest, src) -- Append SRC on the end of DEST.
Optimized for x86-64.
Copyright (C) 2002-2016 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Andreas Jaeger <aj@suse.de>, 2002.
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/>. */
#include <sysdep.h>
#include "asm-syntax.h"
/* Will be removed when new strcpy implementation gets merged. */
.text
ENTRY (strcat)
movq %rdi, %rcx /* Dest. register. */
andl $7, %ecx /* mask alignment bits */
movq %rdi, %rax /* Duplicate destination pointer. */
movq $0xfefefefefefefeff,%r8
/* First step: Find end of destination. */
jz 4f /* aligned => start loop */
neg %ecx /* We need to align to 8 bytes. */
addl $8,%ecx
/* Search the first bytes directly. */
0: cmpb $0x0,(%rax) /* is byte NUL? */
je 2f /* yes => start copy */
incq %rax /* increment pointer */
decl %ecx
jnz 0b
/* Now the source is aligned. Scan for NUL byte. */
.p2align 4
4:
/* First unroll. */
movq (%rax), %rcx /* get double word (= 8 bytes) in question */
addq $8,%rax /* adjust pointer for next word */
movq %r8, %rdx /* magic value */
addq %rcx, %rdx /* add the magic value to the word. We get
carry bits reported for each byte which
is *not* 0 */
jnc 3f /* highest byte is NUL => return pointer */
xorq %rcx, %rdx /* (word+magic)^word */
orq %r8, %rdx /* set all non-carry bits */
incq %rdx /* add 1: if one carry bit was *not* set
the addition will not result in 0. */
jnz 3f /* found NUL => return pointer */
/* Second unroll. */
movq (%rax), %rcx /* get double word (= 8 bytes) in question */
addq $8,%rax /* adjust pointer for next word */
movq %r8, %rdx /* magic value */
addq %rcx, %rdx /* add the magic value to the word. We get
carry bits reported for each byte which
is *not* 0 */
jnc 3f /* highest byte is NUL => return pointer */
xorq %rcx, %rdx /* (word+magic)^word */
orq %r8, %rdx /* set all non-carry bits */
incq %rdx /* add 1: if one carry bit was *not* set
the addition will not result in 0. */
jnz 3f /* found NUL => return pointer */
/* Third unroll. */
movq (%rax), %rcx /* get double word (= 8 bytes) in question */
addq $8,%rax /* adjust pointer for next word */
movq %r8, %rdx /* magic value */
addq %rcx, %rdx /* add the magic value to the word. We get
carry bits reported for each byte which
is *not* 0 */
jnc 3f /* highest byte is NUL => return pointer */
xorq %rcx, %rdx /* (word+magic)^word */
orq %r8, %rdx /* set all non-carry bits */
incq %rdx /* add 1: if one carry bit was *not* set
the addition will not result in 0. */
jnz 3f /* found NUL => return pointer */
/* Fourth unroll. */
movq (%rax), %rcx /* get double word (= 8 bytes) in question */
addq $8,%rax /* adjust pointer for next word */
movq %r8, %rdx /* magic value */
addq %rcx, %rdx /* add the magic value to the word. We get
carry bits reported for each byte which
is *not* 0 */
jnc 3f /* highest byte is NUL => return pointer */
xorq %rcx, %rdx /* (word+magic)^word */
orq %r8, %rdx /* set all non-carry bits */
incq %rdx /* add 1: if one carry bit was *not* set
the addition will not result in 0. */
jz 4b /* no NUL found => continue loop */
.p2align 4 /* Align, it's a jump target. */
3: subq $8,%rax /* correct pointer increment. */
testb %cl, %cl /* is first byte NUL? */
jz 2f /* yes => return */
incq %rax /* increment pointer */
testb %ch, %ch /* is second byte NUL? */
jz 2f /* yes => return */
incq %rax /* increment pointer */
testl $0x00ff0000, %ecx /* is third byte NUL? */
jz 2f /* yes => return pointer */
incq %rax /* increment pointer */
testl $0xff000000, %ecx /* is fourth byte NUL? */
jz 2f /* yes => return pointer */
incq %rax /* increment pointer */
shrq $32, %rcx /* look at other half. */
testb %cl, %cl /* is first byte NUL? */
jz 2f /* yes => return */
incq %rax /* increment pointer */
testb %ch, %ch /* is second byte NUL? */
jz 2f /* yes => return */
incq %rax /* increment pointer */
testl $0xff0000, %ecx /* is third byte NUL? */
jz 2f /* yes => return pointer */
incq %rax /* increment pointer */
2:
/* Second step: Copy source to destination. */
movq %rsi, %rcx /* duplicate */
andl $7,%ecx /* mask alignment bits */
movq %rax, %rdx /* move around */
jz 22f /* aligned => start loop */
neg %ecx /* align to 8 bytes. */
addl $8, %ecx
/* Align the source pointer. */
21:
movb (%rsi), %al /* Fetch a byte */
testb %al, %al /* Is it NUL? */
movb %al, (%rdx) /* Store it */
jz 24f /* If it was NUL, done! */
incq %rsi
incq %rdx
decl %ecx
jnz 21b
/* Now the sources is aligned. Unfortunatly we cannot force
to have both source and destination aligned, so ignore the
alignment of the destination. */
.p2align 4
22:
/* 1st unroll. */
movq (%rsi), %rax /* Read double word (8 bytes). */
addq $8, %rsi /* Adjust pointer for next word. */
movq %rax, %r9 /* Save a copy for NUL finding. */
addq %r8, %r9 /* add the magic value to the word. We get
carry bits reported for each byte which
is *not* 0 */
jnc 23f /* highest byte is NUL => return pointer */
xorq %rax, %r9 /* (word+magic)^word */
orq %r8, %r9 /* set all non-carry bits */
incq %r9 /* add 1: if one carry bit was *not* set
the addition will not result in 0. */
jnz 23f /* found NUL => return pointer */
movq %rax, (%rdx) /* Write value to destination. */
addq $8, %rdx /* Adjust pointer. */
/* 2nd unroll. */
movq (%rsi), %rax /* Read double word (8 bytes). */
addq $8, %rsi /* Adjust pointer for next word. */
movq %rax, %r9 /* Save a copy for NUL finding. */
addq %r8, %r9 /* add the magic value to the word. We get
carry bits reported for each byte which
is *not* 0 */
jnc 23f /* highest byte is NUL => return pointer */
xorq %rax, %r9 /* (word+magic)^word */
orq %r8, %r9 /* set all non-carry bits */
incq %r9 /* add 1: if one carry bit was *not* set
the addition will not result in 0. */
jnz 23f /* found NUL => return pointer */
movq %rax, (%rdx) /* Write value to destination. */
addq $8, %rdx /* Adjust pointer. */
/* 3rd unroll. */
movq (%rsi), %rax /* Read double word (8 bytes). */
addq $8, %rsi /* Adjust pointer for next word. */
movq %rax, %r9 /* Save a copy for NUL finding. */
addq %r8, %r9 /* add the magic value to the word. We get
carry bits reported for each byte which
is *not* 0 */
jnc 23f /* highest byte is NUL => return pointer */
xorq %rax, %r9 /* (word+magic)^word */
orq %r8, %r9 /* set all non-carry bits */
incq %r9 /* add 1: if one carry bit was *not* set
the addition will not result in 0. */
jnz 23f /* found NUL => return pointer */
movq %rax, (%rdx) /* Write value to destination. */
addq $8, %rdx /* Adjust pointer. */
/* 4th unroll. */
movq (%rsi), %rax /* Read double word (8 bytes). */
addq $8, %rsi /* Adjust pointer for next word. */
movq %rax, %r9 /* Save a copy for NUL finding. */
addq %r8, %r9 /* add the magic value to the word. We get
carry bits reported for each byte which
is *not* 0 */
jnc 23f /* highest byte is NUL => return pointer */
xorq %rax, %r9 /* (word+magic)^word */
orq %r8, %r9 /* set all non-carry bits */
incq %r9 /* add 1: if one carry bit was *not* set
the addition will not result in 0. */
jnz 23f /* found NUL => return pointer */
movq %rax, (%rdx) /* Write value to destination. */
addq $8, %rdx /* Adjust pointer. */
jmp 22b /* Next iteration. */
/* Do the last few bytes. %rax contains the value to write.
The loop is unrolled twice. */
.p2align 4
23:
movb %al, (%rdx) /* 1st byte. */
testb %al, %al /* Is it NUL. */
jz 24f /* yes, finish. */
incq %rdx /* Increment destination. */
movb %ah, (%rdx) /* 2nd byte. */
testb %ah, %ah /* Is it NUL?. */
jz 24f /* yes, finish. */
incq %rdx /* Increment destination. */
shrq $16, %rax /* Shift... */
jmp 23b /* and look at next two bytes in %rax. */
24:
movq %rdi, %rax /* Source is return value. */
retq
END (strcat)
libc_hidden_builtin_def (strcat)
|
