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1/* Copyright (C) 1991-2019 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
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
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 <http://www.gnu.org/licenses/>. */
20
21#include <string.h>
22#include <stdlib.h>
23
24#undef strlen
25
26#ifndef STRLEN
27# define STRLEN strlen
28#endif
29
30/* Return the length of the null-terminated string STR. Scan for
31 the null terminator quickly by testing four bytes at a time. */
32size_t
33STRLEN (const char *str)
34{
35 const char *char_ptr;
36 const unsigned long int *longword_ptr;
37 unsigned long int longword, himagic, lomagic;
38
39 /* Handle the first few characters by reading one character at a time.
40 Do this until CHAR_PTR is aligned on a longword boundary. */
41 for (char_ptr = str; ((unsigned long int) char_ptr
42 & (sizeof (longword) - 1)) != 0;
43 ++char_ptr)
44 if (*char_ptr == '\0')
45 return char_ptr - str;
46
47 /* All these elucidatory comments refer to 4-byte longwords,
48 but the theory applies equally well to 8-byte longwords. */
49
50 longword_ptr = (unsigned long int *) char_ptr;
51
52 /* Bits 31, 24, 16, and 8 of this number are zero. Call these bits
53 the "holes." Note that there is a hole just to the left of
54 each byte, with an extra at the end:
55
56 bits: 01111110 11111110 11111110 11111111
57 bytes: AAAAAAAA BBBBBBBB CCCCCCCC DDDDDDDD
58
59 The 1-bits make sure that carries propagate to the next 0-bit.
60 The 0-bits provide holes for carries to fall into. */
61 himagic = 0x80808080L;
62 lomagic = 0x01010101L;
63 if (sizeof (longword) > 4)
64 {
65 /* 64-bit version of the magic. */
66 /* Do the shift in two steps to avoid a warning if long has 32 bits. */
67 himagic = ((himagic << 16) << 16) | himagic;
68 lomagic = ((lomagic << 16) << 16) | lomagic;
69 }
70 if (sizeof (longword) > 8)
71 abort ();
72
73 /* Instead of the traditional loop which tests each character,
74 we will test a longword at a time. The tricky part is testing
75 if *any of the four* bytes in the longword in question are zero. */
76 for (;;)
77 {
78 longword = *longword_ptr++;
79
80 if (((longword - lomagic) & ~longword & himagic) != 0)
81 {
82 /* Which of the bytes was the zero? If none of them were, it was
83 a misfire; continue the search. */
84
85 const char *cp = (const char *) (longword_ptr - 1);
86
87 if (cp[0] == 0)
88 return cp - str;
89 if (cp[1] == 0)
90 return cp - str + 1;
91 if (cp[2] == 0)
92 return cp - str + 2;
93 if (cp[3] == 0)
94 return cp - str + 3;
95 if (sizeof (longword) > 4)
96 {
97 if (cp[4] == 0)
98 return cp - str + 4;
99 if (cp[5] == 0)
100 return cp - str + 5;
101 if (cp[6] == 0)
102 return cp - str + 6;
103 if (cp[7] == 0)
104 return cp - str + 7;
105 }
106 }
107 }
108}
109libc_hidden_builtin_def (strlen)
110

Warning: That file was not part of the compilation database. It may have many parsing errors.