ARM: Consolidate with generic unwinder wrapper code
[glibc.git] / string / strlen.c
blobd066bde5777962923b54e2b5e9417ba1aa0b75ab
1 /* Copyright (C) 1991-2015 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).
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.
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.
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/>. */
21 #include <string.h>
22 #include <stdlib.h>
24 #undef strlen
26 /* Return the length of the null-terminated string STR. Scan for
27 the null terminator quickly by testing four bytes at a time. */
28 size_t
29 strlen (const char *str)
31 const char *char_ptr;
32 const unsigned long int *longword_ptr;
33 unsigned long int longword, himagic, lomagic;
35 /* Handle the first few characters by reading one character at a time.
36 Do this until CHAR_PTR is aligned on a longword boundary. */
37 for (char_ptr = str; ((unsigned long int) char_ptr
38 & (sizeof (longword) - 1)) != 0;
39 ++char_ptr)
40 if (*char_ptr == '\0')
41 return char_ptr - str;
43 /* All these elucidatory comments refer to 4-byte longwords,
44 but the theory applies equally well to 8-byte longwords. */
46 longword_ptr = (unsigned long int *) char_ptr;
48 /* Bits 31, 24, 16, and 8 of this number are zero. Call these bits
49 the "holes." Note that there is a hole just to the left of
50 each byte, with an extra at the end:
52 bits: 01111110 11111110 11111110 11111111
53 bytes: AAAAAAAA BBBBBBBB CCCCCCCC DDDDDDDD
55 The 1-bits make sure that carries propagate to the next 0-bit.
56 The 0-bits provide holes for carries to fall into. */
57 himagic = 0x80808080L;
58 lomagic = 0x01010101L;
59 if (sizeof (longword) > 4)
61 /* 64-bit version of the magic. */
62 /* Do the shift in two steps to avoid a warning if long has 32 bits. */
63 himagic = ((himagic << 16) << 16) | himagic;
64 lomagic = ((lomagic << 16) << 16) | lomagic;
66 if (sizeof (longword) > 8)
67 abort ();
69 /* Instead of the traditional loop which tests each character,
70 we will test a longword at a time. The tricky part is testing
71 if *any of the four* bytes in the longword in question are zero. */
72 for (;;)
74 longword = *longword_ptr++;
76 if (((longword - lomagic) & ~longword & himagic) != 0)
78 /* Which of the bytes was the zero? If none of them were, it was
79 a misfire; continue the search. */
81 const char *cp = (const char *) (longword_ptr - 1);
83 if (cp[0] == 0)
84 return cp - str;
85 if (cp[1] == 0)
86 return cp - str + 1;
87 if (cp[2] == 0)
88 return cp - str + 2;
89 if (cp[3] == 0)
90 return cp - str + 3;
91 if (sizeof (longword) > 4)
93 if (cp[4] == 0)
94 return cp - str + 4;
95 if (cp[5] == 0)
96 return cp - str + 5;
97 if (cp[6] == 0)
98 return cp - str + 6;
99 if (cp[7] == 0)
100 return cp - str + 7;
105 libc_hidden_builtin_def (strlen)