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authorUlrich Drepper <drepper@redhat.com>2004-12-22 20:10:10 +0000
committerUlrich Drepper <drepper@redhat.com>2004-12-22 20:10:10 +0000
commita334319f6530564d22e775935d9c91663623a1b4 (patch)
treeb5877475619e4c938e98757d518bb1e9cbead751 /string/strnlen.c
parent0ecb606cb6cf65de1d9fc8a919bceb4be476c602 (diff)
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(CFLAGS-tst-align.c): Add -mpreferred-stack-boundary=4.
Diffstat (limited to 'string/strnlen.c')
-rw-r--r--string/strnlen.c161
1 files changed, 0 insertions, 161 deletions
diff --git a/string/strnlen.c b/string/strnlen.c
deleted file mode 100644
index 454257b..0000000
--- a/string/strnlen.c
+++ /dev/null
@@ -1,161 +0,0 @@
-/* Find the length of STRING, but scan at most MAXLEN characters.
- Copyright (C) 1991,1993,1997,2000,2001,2005 Free Software Foundation, Inc.
- Contributed by Jakub Jelinek <jakub@redhat.com>.
-
- Based on strlen written by Torbjorn Granlund (tege@sics.se),
- with help from Dan Sahlin (dan@sics.se);
- commentary by Jim Blandy (jimb@ai.mit.edu).
-
- The GNU C Library is free software; you can redistribute it and/or
- modify it under the terms of the GNU Lesser General Public License as
- published by the Free Software Foundation; either version 2.1 of the
- License, or (at your option) any later version.
-
- The GNU C Library is distributed in the hope that it will be useful,
- but WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- Lesser General Public License for more details.
-
- You should have received a copy of the GNU Lesser General Public
- License along with the GNU C Library; see the file COPYING.LIB. If not,
- write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
- Boston, MA 02111-1307, USA. */
-
-#include <string.h>
-#include <stdlib.h>
-
-/* Find the length of S, but scan at most MAXLEN characters. If no
- '\0' terminator is found in that many characters, return MAXLEN. */
-size_t
-__strnlen (const char *str, size_t maxlen)
-{
- const char *char_ptr, *end_ptr = str + maxlen;
- const unsigned long int *longword_ptr;
- unsigned long int longword, magic_bits, himagic, lomagic;
-
- if (maxlen == 0)
- return 0;
-
- if (__builtin_expect (end_ptr < str, 0))
- end_ptr = (const char *) ~0UL;
-
- /* Handle the first few characters by reading one character at a time.
- Do this until CHAR_PTR is aligned on a longword boundary. */
- for (char_ptr = str; ((unsigned long int) char_ptr
- & (sizeof (longword) - 1)) != 0;
- ++char_ptr)
- if (*char_ptr == '\0')
- {
- if (char_ptr > end_ptr)
- char_ptr = end_ptr;
- return char_ptr - str;
- }
-
- /* All these elucidatory comments refer to 4-byte longwords,
- but the theory applies equally well to 8-byte longwords. */
-
- longword_ptr = (unsigned long int *) char_ptr;
-
- /* Bits 31, 24, 16, and 8 of this number are zero. Call these bits
- the "holes." Note that there is a hole just to the left of
- each byte, with an extra at the end:
-
- bits: 01111110 11111110 11111110 11111111
- bytes: AAAAAAAA BBBBBBBB CCCCCCCC DDDDDDDD
-
- The 1-bits make sure that carries propagate to the next 0-bit.
- The 0-bits provide holes for carries to fall into. */
- magic_bits = 0x7efefeffL;
- himagic = 0x80808080L;
- lomagic = 0x01010101L;
- if (sizeof (longword) > 4)
- {
- /* 64-bit version of the magic. */
- /* Do the shift in two steps to avoid a warning if long has 32 bits. */
- magic_bits = ((0x7efefefeL << 16) << 16) | 0xfefefeffL;
- himagic = ((himagic << 16) << 16) | himagic;
- lomagic = ((lomagic << 16) << 16) | lomagic;
- }
- if (sizeof (longword) > 8)
- abort ();
-
- /* Instead of the traditional loop which tests each character,
- we will test a longword at a time. The tricky part is testing
- if *any of the four* bytes in the longword in question are zero. */
- while (longword_ptr < (unsigned long int *) end_ptr)
- {
- /* We tentatively exit the loop if adding MAGIC_BITS to
- LONGWORD fails to change any of the hole bits of LONGWORD.
-
- 1) Is this safe? Will it catch all the zero bytes?
- Suppose there is a byte with all zeros. Any carry bits
- propagating from its left will fall into the hole at its
- least significant bit and stop. Since there will be no
- carry from its most significant bit, the LSB of the
- byte to the left will be unchanged, and the zero will be
- detected.
-
- 2) Is this worthwhile? Will it ignore everything except
- zero bytes? Suppose every byte of LONGWORD has a bit set
- somewhere. There will be a carry into bit 8. If bit 8
- is set, this will carry into bit 16. If bit 8 is clear,
- one of bits 9-15 must be set, so there will be a carry
- into bit 16. Similarly, there will be a carry into bit
- 24. If one of bits 24-30 is set, there will be a carry
- into bit 31, so all of the hole bits will be changed.
-
- The one misfire occurs when bits 24-30 are clear and bit
- 31 is set; in this case, the hole at bit 31 is not
- changed. If we had access to the processor carry flag,
- we could close this loophole by putting the fourth hole
- at bit 32!
-
- So it ignores everything except 128's, when they're aligned
- properly. */
-
- longword = *longword_ptr++;
-
- if ((longword - lomagic) & himagic)
- {
- /* Which of the bytes was the zero? If none of them were, it was
- a misfire; continue the search. */
-
- const char *cp = (const char *) (longword_ptr - 1);
-
- char_ptr = cp;
- if (cp[0] == 0)
- break;
- char_ptr = cp + 1;
- if (cp[1] == 0)
- break;
- char_ptr = cp + 2;
- if (cp[2] == 0)
- break;
- char_ptr = cp + 3;
- if (cp[3] == 0)
- break;
- if (sizeof (longword) > 4)
- {
- char_ptr = cp + 4;
- if (cp[4] == 0)
- break;
- char_ptr = cp + 5;
- if (cp[5] == 0)
- break;
- char_ptr = cp + 6;
- if (cp[6] == 0)
- break;
- char_ptr = cp + 7;
- if (cp[7] == 0)
- break;
- }
- }
- char_ptr = end_ptr;
- }
-
- if (char_ptr > end_ptr)
- char_ptr = end_ptr;
- return char_ptr - str;
-}
-weak_alias (__strnlen, strnlen)
-libc_hidden_def (strnlen)