1/* strcat(dest, src) -- Append SRC on the end of DEST.
2 Optimized for x86-64.
3 Copyright (C) 2002-2021 Free Software Foundation, Inc.
4 This file is part of the GNU C Library.
5 Contributed by Andreas Jaeger <aj@suse.de>, 2002.
6
7 The GNU C Library is free software; you can redistribute it and/or
8 modify it under the terms of the GNU Lesser General Public
9 License as published by the Free Software Foundation; either
10 version 2.1 of the License, or (at your option) any later version.
11
12 The GNU C Library is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 Lesser General Public License for more details.
16
17 You should have received a copy of the GNU Lesser General Public
18 License along with the GNU C Library; if not, see
19 <https://www.gnu.org/licenses/>. */
20
21#include <sysdep.h>
22#include "asm-syntax.h"
23
24/* Will be removed when new strcpy implementation gets merged. */
25
26 .text
27ENTRY (strcat)
28 movq %rdi, %rcx /* Dest. register. */
29 andl $7, %ecx /* mask alignment bits */
30 movq %rdi, %rax /* Duplicate destination pointer. */
31 movq $0xfefefefefefefeff,%r8
32
33 /* First step: Find end of destination. */
34 jz 4f /* aligned => start loop */
35
36 neg %ecx /* We need to align to 8 bytes. */
37 addl $8,%ecx
38 /* Search the first bytes directly. */
390: cmpb $0x0,(%rax) /* is byte NUL? */
40 je 2f /* yes => start copy */
41 incq %rax /* increment pointer */
42 decl %ecx
43 jnz 0b
44
45
46
47 /* Now the source is aligned. Scan for NUL byte. */
48 .p2align 4
494:
50 /* First unroll. */
51 movq (%rax), %rcx /* get double word (= 8 bytes) in question */
52 addq $8,%rax /* adjust pointer for next word */
53 movq %r8, %rdx /* magic value */
54 addq %rcx, %rdx /* add the magic value to the word. We get
55 carry bits reported for each byte which
56 is *not* 0 */
57 jnc 3f /* highest byte is NUL => return pointer */
58 xorq %rcx, %rdx /* (word+magic)^word */
59 orq %r8, %rdx /* set all non-carry bits */
60 incq %rdx /* add 1: if one carry bit was *not* set
61 the addition will not result in 0. */
62 jnz 3f /* found NUL => return pointer */
63
64 /* Second unroll. */
65 movq (%rax), %rcx /* get double word (= 8 bytes) in question */
66 addq $8,%rax /* adjust pointer for next word */
67 movq %r8, %rdx /* magic value */
68 addq %rcx, %rdx /* add the magic value to the word. We get
69 carry bits reported for each byte which
70 is *not* 0 */
71 jnc 3f /* highest byte is NUL => return pointer */
72 xorq %rcx, %rdx /* (word+magic)^word */
73 orq %r8, %rdx /* set all non-carry bits */
74 incq %rdx /* add 1: if one carry bit was *not* set
75 the addition will not result in 0. */
76 jnz 3f /* found NUL => return pointer */
77
78 /* Third unroll. */
79 movq (%rax), %rcx /* get double word (= 8 bytes) in question */
80 addq $8,%rax /* adjust pointer for next word */
81 movq %r8, %rdx /* magic value */
82 addq %rcx, %rdx /* add the magic value to the word. We get
83 carry bits reported for each byte which
84 is *not* 0 */
85 jnc 3f /* highest byte is NUL => return pointer */
86 xorq %rcx, %rdx /* (word+magic)^word */
87 orq %r8, %rdx /* set all non-carry bits */
88 incq %rdx /* add 1: if one carry bit was *not* set
89 the addition will not result in 0. */
90 jnz 3f /* found NUL => return pointer */
91
92 /* Fourth unroll. */
93 movq (%rax), %rcx /* get double word (= 8 bytes) in question */
94 addq $8,%rax /* adjust pointer for next word */
95 movq %r8, %rdx /* magic value */
96 addq %rcx, %rdx /* add the magic value to the word. We get
97 carry bits reported for each byte which
98 is *not* 0 */
99 jnc 3f /* highest byte is NUL => return pointer */
100 xorq %rcx, %rdx /* (word+magic)^word */
101 orq %r8, %rdx /* set all non-carry bits */
102 incq %rdx /* add 1: if one carry bit was *not* set
103 the addition will not result in 0. */
104 jz 4b /* no NUL found => continue loop */
105
106 .p2align 4 /* Align, it's a jump target. */
1073: subq $8,%rax /* correct pointer increment. */
108
109 testb %cl, %cl /* is first byte NUL? */
110 jz 2f /* yes => return */
111 incq %rax /* increment pointer */
112
113 testb %ch, %ch /* is second byte NUL? */
114 jz 2f /* yes => return */
115 incq %rax /* increment pointer */
116
117 testl $0x00ff0000, %ecx /* is third byte NUL? */
118 jz 2f /* yes => return pointer */
119 incq %rax /* increment pointer */
120
121 testl $0xff000000, %ecx /* is fourth byte NUL? */
122 jz 2f /* yes => return pointer */
123 incq %rax /* increment pointer */
124
125 shrq $32, %rcx /* look at other half. */
126
127 testb %cl, %cl /* is first byte NUL? */
128 jz 2f /* yes => return */
129 incq %rax /* increment pointer */
130
131 testb %ch, %ch /* is second byte NUL? */
132 jz 2f /* yes => return */
133 incq %rax /* increment pointer */
134
135 testl $0xff0000, %ecx /* is third byte NUL? */
136 jz 2f /* yes => return pointer */
137 incq %rax /* increment pointer */
138
1392:
140 /* Second step: Copy source to destination. */
141
142 movq %rsi, %rcx /* duplicate */
143 andl $7,%ecx /* mask alignment bits */
144 movq %rax, %rdx /* move around */
145 jz 22f /* aligned => start loop */
146
147 neg %ecx /* align to 8 bytes. */
148 addl $8, %ecx
149 /* Align the source pointer. */
15021:
151 movb (%rsi), %al /* Fetch a byte */
152 testb %al, %al /* Is it NUL? */
153 movb %al, (%rdx) /* Store it */
154 jz 24f /* If it was NUL, done! */
155 incq %rsi
156 incq %rdx
157 decl %ecx
158 jnz 21b
159
160 /* Now the sources is aligned. Unfortunatly we cannot force
161 to have both source and destination aligned, so ignore the
162 alignment of the destination. */
163 .p2align 4
16422:
165 /* 1st unroll. */
166 movq (%rsi), %rax /* Read double word (8 bytes). */
167 addq $8, %rsi /* Adjust pointer for next word. */
168 movq %rax, %r9 /* Save a copy for NUL finding. */
169 addq %r8, %r9 /* add the magic value to the word. We get
170 carry bits reported for each byte which
171 is *not* 0 */
172 jnc 23f /* highest byte is NUL => return pointer */
173 xorq %rax, %r9 /* (word+magic)^word */
174 orq %r8, %r9 /* set all non-carry bits */
175 incq %r9 /* add 1: if one carry bit was *not* set
176 the addition will not result in 0. */
177
178 jnz 23f /* found NUL => return pointer */
179
180 movq %rax, (%rdx) /* Write value to destination. */
181 addq $8, %rdx /* Adjust pointer. */
182
183 /* 2nd unroll. */
184 movq (%rsi), %rax /* Read double word (8 bytes). */
185 addq $8, %rsi /* Adjust pointer for next word. */
186 movq %rax, %r9 /* Save a copy for NUL finding. */
187 addq %r8, %r9 /* add the magic value to the word. We get
188 carry bits reported for each byte which
189 is *not* 0 */
190 jnc 23f /* highest byte is NUL => return pointer */
191 xorq %rax, %r9 /* (word+magic)^word */
192 orq %r8, %r9 /* set all non-carry bits */
193 incq %r9 /* add 1: if one carry bit was *not* set
194 the addition will not result in 0. */
195
196 jnz 23f /* found NUL => return pointer */
197
198 movq %rax, (%rdx) /* Write value to destination. */
199 addq $8, %rdx /* Adjust pointer. */
200
201 /* 3rd unroll. */
202 movq (%rsi), %rax /* Read double word (8 bytes). */
203 addq $8, %rsi /* Adjust pointer for next word. */
204 movq %rax, %r9 /* Save a copy for NUL finding. */
205 addq %r8, %r9 /* add the magic value to the word. We get
206 carry bits reported for each byte which
207 is *not* 0 */
208 jnc 23f /* highest byte is NUL => return pointer */
209 xorq %rax, %r9 /* (word+magic)^word */
210 orq %r8, %r9 /* set all non-carry bits */
211 incq %r9 /* add 1: if one carry bit was *not* set
212 the addition will not result in 0. */
213
214 jnz 23f /* found NUL => return pointer */
215
216 movq %rax, (%rdx) /* Write value to destination. */
217 addq $8, %rdx /* Adjust pointer. */
218
219 /* 4th unroll. */
220 movq (%rsi), %rax /* Read double word (8 bytes). */
221 addq $8, %rsi /* Adjust pointer for next word. */
222 movq %rax, %r9 /* Save a copy for NUL finding. */
223 addq %r8, %r9 /* add the magic value to the word. We get
224 carry bits reported for each byte which
225 is *not* 0 */
226 jnc 23f /* highest byte is NUL => return pointer */
227 xorq %rax, %r9 /* (word+magic)^word */
228 orq %r8, %r9 /* set all non-carry bits */
229 incq %r9 /* add 1: if one carry bit was *not* set
230 the addition will not result in 0. */
231
232 jnz 23f /* found NUL => return pointer */
233
234 movq %rax, (%rdx) /* Write value to destination. */
235 addq $8, %rdx /* Adjust pointer. */
236 jmp 22b /* Next iteration. */
237
238 /* Do the last few bytes. %rax contains the value to write.
239 The loop is unrolled twice. */
240 .p2align 4
24123:
242 movb %al, (%rdx) /* 1st byte. */
243 testb %al, %al /* Is it NUL. */
244 jz 24f /* yes, finish. */
245 incq %rdx /* Increment destination. */
246 movb %ah, (%rdx) /* 2nd byte. */
247 testb %ah, %ah /* Is it NUL?. */
248 jz 24f /* yes, finish. */
249 incq %rdx /* Increment destination. */
250 shrq $16, %rax /* Shift... */
251 jmp 23b /* and look at next two bytes in %rax. */
252
253
25424:
255 movq %rdi, %rax /* Source is return value. */
256 retq
257END (strcat)
258libc_hidden_builtin_def (strcat)
259