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).
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/>. */
27 # define STRLEN strlen
30 /* Return the length of the null-terminated string STR. Scan for
31 the null terminator quickly by testing four bytes at a time. */
33 STRLEN (const char *str
)
36 const unsigned long int *longword_ptr
;
37 unsigned long int longword
, himagic
, lomagic
;
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;
44 if (*char_ptr
== '\0')
45 return char_ptr
- str
;
47 /* All these elucidatory comments refer to 4-byte longwords,
48 but the theory applies equally well to 8-byte longwords. */
50 longword_ptr
= (unsigned long int *) char_ptr
;
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:
56 bits: 01111110 11111110 11111110 11111111
57 bytes: AAAAAAAA BBBBBBBB CCCCCCCC DDDDDDDD
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)
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
;
70 if (sizeof (longword
) > 8)
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. */
78 longword
= *longword_ptr
++;
80 if (((longword
- lomagic
) & ~longword
& himagic
) != 0)
82 /* Which of the bytes was the zero? If none of them were, it was
83 a misfire; continue the search. */
85 const char *cp
= (const char *) (longword_ptr
- 1);
95 if (sizeof (longword
) > 4)
109 libc_hidden_builtin_def (strlen
)