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 |
27 | ENTRY (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. */ |
37 | 0: |
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 | |
47 | 5: |
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 |
54 | 1: |
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 |
131 | 3: |
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 | |
145 | 4: |
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 |
152 | END (STRCPY) |
153 | #ifndef USE_AS_STPCPY |
154 | libc_hidden_builtin_def (strcpy) |
155 | #endif |
156 | |