1/* strcpy/stpcpy implementation for x86-64.
2 Copyright (C) 2002-2022 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19#include <sysdep.h>
20#include "asm-syntax.h"
21
22#ifndef USE_AS_STPCPY
23# define STRCPY strcpy
24#endif
25
26 .text
27ENTRY (STRCPY)
28 movq %rsi, %rcx /* Source register. */
29 andl $7, %ecx /* mask alignment bits */
30 movq %rdi, %rdx /* Duplicate destination pointer. */
31
32 jz 5f /* aligned => start loop */
33
34 neg %ecx /* We need to align to 8 bytes. */
35 addl $8,%ecx
36 /* Search the first bytes directly. */
370:
38 movb (%rsi), %al /* Fetch a byte */
39 testb %al, %al /* Is it NUL? */
40 movb %al, (%rdx) /* Store it */
41 jz 4f /* If it was NUL, done! */
42 incq %rsi
43 incq %rdx
44 decl %ecx
45 jnz 0b
46
475:
48 movq $0xfefefefefefefeff,%r8
49
50 /* Now the sources is aligned. Unfortunatly we cannot force
51 to have both source and destination aligned, so ignore the
52 alignment of the destination. */
53 .p2align 4
541:
55 /* 1st unroll. */
56 movq (%rsi), %rax /* Read double word (8 bytes). */
57 addq $8, %rsi /* Adjust pointer for next word. */
58 movq %rax, %r9 /* Save a copy for NUL finding. */
59 addq %r8, %r9 /* add the magic value to the word. We get
60 carry bits reported for each byte which
61 is *not* 0 */
62 jnc 3f /* highest byte is NUL => return pointer */
63 xorq %rax, %r9 /* (word+magic)^word */
64 orq %r8, %r9 /* set all non-carry bits */
65 incq %r9 /* add 1: if one carry bit was *not* set
66 the addition will not result in 0. */
67
68 jnz 3f /* found NUL => return pointer */
69
70 movq %rax, (%rdx) /* Write value to destination. */
71 addq $8, %rdx /* Adjust pointer. */
72
73 /* 2nd unroll. */
74 movq (%rsi), %rax /* Read double word (8 bytes). */
75 addq $8, %rsi /* Adjust pointer for next word. */
76 movq %rax, %r9 /* Save a copy for NUL finding. */
77 addq %r8, %r9 /* add the magic value to the word. We get
78 carry bits reported for each byte which
79 is *not* 0 */
80 jnc 3f /* highest byte is NUL => return pointer */
81 xorq %rax, %r9 /* (word+magic)^word */
82 orq %r8, %r9 /* set all non-carry bits */
83 incq %r9 /* add 1: if one carry bit was *not* set
84 the addition will not result in 0. */
85
86 jnz 3f /* found NUL => return pointer */
87
88 movq %rax, (%rdx) /* Write value to destination. */
89 addq $8, %rdx /* Adjust pointer. */
90
91 /* 3rd unroll. */
92 movq (%rsi), %rax /* Read double word (8 bytes). */
93 addq $8, %rsi /* Adjust pointer for next word. */
94 movq %rax, %r9 /* Save a copy for NUL finding. */
95 addq %r8, %r9 /* add the magic value to the word. We get
96 carry bits reported for each byte which
97 is *not* 0 */
98 jnc 3f /* highest byte is NUL => return pointer */
99 xorq %rax, %r9 /* (word+magic)^word */
100 orq %r8, %r9 /* set all non-carry bits */
101 incq %r9 /* add 1: if one carry bit was *not* set
102 the addition will not result in 0. */
103
104 jnz 3f /* found NUL => return pointer */
105
106 movq %rax, (%rdx) /* Write value to destination. */
107 addq $8, %rdx /* Adjust pointer. */
108
109 /* 4th unroll. */
110 movq (%rsi), %rax /* Read double word (8 bytes). */
111 addq $8, %rsi /* Adjust pointer for next word. */
112 movq %rax, %r9 /* Save a copy for NUL finding. */
113 addq %r8, %r9 /* add the magic value to the word. We get
114 carry bits reported for each byte which
115 is *not* 0 */
116 jnc 3f /* highest byte is NUL => return pointer */
117 xorq %rax, %r9 /* (word+magic)^word */
118 orq %r8, %r9 /* set all non-carry bits */
119 incq %r9 /* add 1: if one carry bit was *not* set
120 the addition will not result in 0. */
121
122 jnz 3f /* found NUL => return pointer */
123
124 movq %rax, (%rdx) /* Write value to destination. */
125 addq $8, %rdx /* Adjust pointer. */
126 jmp 1b /* Next iteration. */
127
128 /* Do the last few bytes. %rax contains the value to write.
129 The loop is unrolled twice. */
130 .p2align 4
1313:
132 /* Note that stpcpy needs to return with the value of the NUL
133 byte. */
134 movb %al, (%rdx) /* 1st byte. */
135 testb %al, %al /* Is it NUL. */
136 jz 4f /* yes, finish. */
137 incq %rdx /* Increment destination. */
138 movb %ah, (%rdx) /* 2nd byte. */
139 testb %ah, %ah /* Is it NUL?. */
140 jz 4f /* yes, finish. */
141 incq %rdx /* Increment destination. */
142 shrq $16, %rax /* Shift... */
143 jmp 3b /* and look at next two bytes in %rax. */
144
1454:
146#ifdef USE_AS_STPCPY
147 movq %rdx, %rax /* Destination is return value. */
148#else
149 movq %rdi, %rax /* Source is return value. */
150#endif
151 retq
152END (STRCPY)
153#ifndef USE_AS_STPCPY
154libc_hidden_builtin_def (strcpy)
155#endif
156

source code of glibc/sysdeps/x86_64/strcpy.S