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d4697bc9 | 1 | /* Copyright (C) 1991-2014 Free Software Foundation, Inc. |
41bdb6e2 | 2 | This file is part of the GNU C Library. |
28f540f4 RM |
3 | Written by Torbjorn Granlund (tege@sics.se), |
4 | with help from Dan Sahlin (dan@sics.se); | |
5 | commentary by Jim Blandy (jimb@ai.mit.edu). | |
6 | ||
c84142e8 | 7 | The GNU C Library is free software; you can redistribute it and/or |
41bdb6e2 AJ |
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. | |
28f540f4 | 11 | |
c84142e8 UD |
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 | |
41bdb6e2 | 15 | Lesser General Public License for more details. |
28f540f4 | 16 | |
41bdb6e2 | 17 | You should have received a copy of the GNU Lesser General Public |
59ba27a6 PE |
18 | License along with the GNU C Library; if not, see |
19 | <http://www.gnu.org/licenses/>. */ | |
28f540f4 | 20 | |
28f540f4 | 21 | #include <string.h> |
a2616aed | 22 | #include <stdlib.h> |
28f540f4 | 23 | |
9a0a462c | 24 | #undef strlen |
28f540f4 RM |
25 | |
26 | /* Return the length of the null-terminated string STR. Scan for | |
27 | the null terminator quickly by testing four bytes at a time. */ | |
28f540f4 | 28 | size_t |
c84142e8 UD |
29 | strlen (str) |
30 | const char *str; | |
28f540f4 | 31 | { |
c84142e8 UD |
32 | const char *char_ptr; |
33 | const unsigned long int *longword_ptr; | |
71a5bd3e | 34 | unsigned long int longword, himagic, lomagic; |
28f540f4 RM |
35 | |
36 | /* Handle the first few characters by reading one character at a time. | |
37 | Do this until CHAR_PTR is aligned on a longword boundary. */ | |
38 | for (char_ptr = str; ((unsigned long int) char_ptr | |
39 | & (sizeof (longword) - 1)) != 0; | |
40 | ++char_ptr) | |
41 | if (*char_ptr == '\0') | |
42 | return char_ptr - str; | |
43 | ||
44 | /* All these elucidatory comments refer to 4-byte longwords, | |
45 | but the theory applies equally well to 8-byte longwords. */ | |
46 | ||
47 | longword_ptr = (unsigned long int *) char_ptr; | |
48 | ||
49 | /* Bits 31, 24, 16, and 8 of this number are zero. Call these bits | |
50 | the "holes." Note that there is a hole just to the left of | |
51 | each byte, with an extra at the end: | |
c84142e8 | 52 | |
28f540f4 | 53 | bits: 01111110 11111110 11111110 11111111 |
c84142e8 | 54 | bytes: AAAAAAAA BBBBBBBB CCCCCCCC DDDDDDDD |
28f540f4 RM |
55 | |
56 | The 1-bits make sure that carries propagate to the next 0-bit. | |
57 | The 0-bits provide holes for carries to fall into. */ | |
28f540f4 RM |
58 | himagic = 0x80808080L; |
59 | lomagic = 0x01010101L; | |
60 | if (sizeof (longword) > 4) | |
61 | { | |
62 | /* 64-bit version of the magic. */ | |
dfd2257a | 63 | /* Do the shift in two steps to avoid a warning if long has 32 bits. */ |
dfd2257a UD |
64 | himagic = ((himagic << 16) << 16) | himagic; |
65 | lomagic = ((lomagic << 16) << 16) | lomagic; | |
28f540f4 RM |
66 | } |
67 | if (sizeof (longword) > 8) | |
68 | abort (); | |
69 | ||
70 | /* Instead of the traditional loop which tests each character, | |
71 | we will test a longword at a time. The tricky part is testing | |
72 | if *any of the four* bytes in the longword in question are zero. */ | |
73 | for (;;) | |
74 | { | |
28f540f4 RM |
75 | longword = *longword_ptr++; |
76 | ||
71a5bd3e | 77 | if (((longword - lomagic) & ~longword & himagic) != 0) |
28f540f4 RM |
78 | { |
79 | /* Which of the bytes was the zero? If none of them were, it was | |
80 | a misfire; continue the search. */ | |
81 | ||
c84142e8 | 82 | const char *cp = (const char *) (longword_ptr - 1); |
28f540f4 RM |
83 | |
84 | if (cp[0] == 0) | |
85 | return cp - str; | |
86 | if (cp[1] == 0) | |
87 | return cp - str + 1; | |
88 | if (cp[2] == 0) | |
89 | return cp - str + 2; | |
90 | if (cp[3] == 0) | |
91 | return cp - str + 3; | |
92 | if (sizeof (longword) > 4) | |
93 | { | |
94 | if (cp[4] == 0) | |
95 | return cp - str + 4; | |
96 | if (cp[5] == 0) | |
97 | return cp - str + 5; | |
98 | if (cp[6] == 0) | |
99 | return cp - str + 6; | |
100 | if (cp[7] == 0) | |
101 | return cp - str + 7; | |
102 | } | |
103 | } | |
104 | } | |
105 | } | |
85dd1003 | 106 | libc_hidden_builtin_def (strlen) |