diff options
| -rw-r--r-- | manual/string.texi | 7 | ||||
| -rw-r--r-- | string/string.h | 4 | ||||
| -rw-r--r-- | sysdeps/generic/memrchr.c | 201 | ||||
| -rw-r--r-- | sysdeps/i386/bits/string.h | 21 |
4 files changed, 233 insertions, 0 deletions
diff --git a/manual/string.texi b/manual/string.texi index a151ddd48c..2d28dd2e47 100644 --- a/manual/string.texi +++ b/manual/string.texi @@ -1063,6 +1063,13 @@ located byte, or a null pointer if no match was found. @end deftypefun @comment string.h +@comment GNU +@deftypefun {void *} memrchr (const void *@var{block}, int @var{c}, size_t @var{size}) +The function @code{memrchr} is like @code{memchr}, except that it searches +backwards from the end of the block defined by @var{block} and @var{size} +(instead of forwards from the front). + +@comment string.h @comment ISO @deftypefun {char *} strchr (const char *@var{string}, int @var{c}) The @code{strchr} function finds the first occurrence of the character diff --git a/string/string.h b/string/string.h index 6c913a85c6..03cf103ad6 100644 --- a/string/string.h +++ b/string/string.h @@ -64,6 +64,10 @@ extern __ptr_t memchr __P ((__const __ptr_t __s, int __c, size_t __n)); /* Search in S for C. This is similar to `memchr' but there is no length limit. */ extern __ptr_t rawmemchr __P ((__const __ptr_t __s, int __c)); + +/* Search N bytes of S for the final occurrence of C. */ +extern __ptr_t __memrchr __P ((__const __ptr_t __s, int __c, size_t __n)); +extern __ptr_t memrchr __P ((__const __ptr_t __s, int __c, size_t __n)); #endif diff --git a/sysdeps/generic/memrchr.c b/sysdeps/generic/memrchr.c new file mode 100644 index 0000000000..4b9f92e3fe --- /dev/null +++ b/sysdeps/generic/memrchr.c @@ -0,0 +1,201 @@ +/* memrchr -- find the last occurrence of a byte in a memory block + Copyright (C) 1991, 1993, 1996, 1997, 1999 Free Software Foundation, Inc. + Based on strlen implementation by Torbjorn Granlund (tege@sics.se), + with help from Dan Sahlin (dan@sics.se) and + commentary by Jim Blandy (jimb@ai.mit.edu); + adaptation to memchr suggested by Dick Karpinski (dick@cca.ucsf.edu), + and implemented by Roland McGrath (roland@ai.mit.edu). + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Library General Public License as + published by the Free Software Foundation; either version 2 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 + Library General Public License for more details. + + You should have received a copy of the GNU Library 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. */ + +#ifdef HAVE_CONFIG_H +#include <config.h> +#endif + +#undef __ptr_t +#if defined (__cplusplus) || (defined (__STDC__) && __STDC__) +# define __ptr_t void * +#else /* Not C++ or ANSI C. */ +# define __ptr_t char * +#endif /* C++ or ANSI C. */ + +#if defined (_LIBC) +# include <string.h> +# include <memcopy.h> +#else +# define reg_char char +#endif + +#if defined (HAVE_LIMITS_H) || defined (_LIBC) +# include <limits.h> +#endif + +#define LONG_MAX_32_BITS 2147483647 + +#ifndef LONG_MAX +#define LONG_MAX LONG_MAX_32_BITS +#endif + +#include <sys/types.h> + +#undef memchr + + +/* Search no more than N bytes of S for C. */ +__ptr_t +__memrchr (s, c_in, n) + const __ptr_t s; + int c_in; + size_t n; +{ + const unsigned char *char_ptr; + const unsigned long int *longword_ptr; + unsigned long int longword, magic_bits, charmask; + unsigned reg_char c; + + c = (unsigned char) c_in; + + /* Handle the last few characters by reading one character at a time. + Do this until CHAR_PTR is aligned on a longword boundary. */ + for (char_ptr = (const unsigned char *) s + n; + n > 0 && ((unsigned long int) char_ptr + & (sizeof (longword) - 1)) != 0; + --n) + if (*--char_ptr == c) + return (__ptr_t) char_ptr; + + /* 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. */ + + if (sizeof (longword) != 4 && sizeof (longword) != 8) + abort (); + +#if LONG_MAX <= LONG_MAX_32_BITS + magic_bits = 0x7efefeff; +#else + magic_bits = ((unsigned long int) 0x7efefefe << 32) | 0xfefefeff; +#endif + + /* Set up a longword, each of whose bytes is C. */ + charmask = c | (c << 8); + charmask |= charmask << 16; +#if LONG_MAX > LONG_MAX_32_BITS + charmask |= charmask << 32; +#endif + + /* 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 (n >= sizeof (longword)) + { + /* 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. + + 3) But wait! Aren't we looking for C, not zero? + Good point. So what we do is XOR LONGWORD with a longword, + each of whose bytes is C. This turns each byte that is C + into a zero. */ + + longword = *--longword_ptr ^ charmask; + + /* Add MAGIC_BITS to LONGWORD. */ + if ((((longword + magic_bits) + + /* Set those bits that were unchanged by the addition. */ + ^ ~longword) + + /* Look at only the hole bits. If any of the hole bits + are unchanged, most likely one of the bytes was a + zero. */ + & ~magic_bits) != 0) + { + /* Which of the bytes was C? If none of them were, it was + a misfire; continue the search. */ + + const unsigned char *cp = (const unsigned char *) longword_ptr; + + if (cp[0] == c) + return (__ptr_t) cp; + if (cp[1] == c) + return (__ptr_t) &cp[1]; + if (cp[2] == c) + return (__ptr_t) &cp[2]; + if (cp[3] == c) + return (__ptr_t) &cp[3]; +#if LONG_MAX > 2147483647 + if (cp[4] == c) + return (__ptr_t) &cp[4]; + if (cp[5] == c) + return (__ptr_t) &cp[5]; + if (cp[6] == c) + return (__ptr_t) &cp[6]; + if (cp[7] == c) + return (__ptr_t) &cp[7]; +#endif + } + + n -= sizeof (longword); + } + + char_ptr = (const unsigned char *) longword_ptr; + + while (n-- > 0) + { + if (*--char_ptr == c) + return (__ptr_t) char_ptr; + } + + return 0; +} +weak_alias (__memrchr, memrchr) diff --git a/sysdeps/i386/bits/string.h b/sysdeps/i386/bits/string.h index 44d6f8ba43..6fc78b3799 100644 --- a/sysdeps/i386/bits/string.h +++ b/sysdeps/i386/bits/string.h @@ -305,6 +305,27 @@ memchr (__const void *__s, int __c, size_t __n) } #endif +#define _HAVE_STRING_ARCH_memrchr 1 +#ifndef _FORCE_INLINES +__STRING_INLINE void * +__memrchr (__const void *__s, int __c, size_t __n) +{ + register unsigned long int __d0; + register void *__res; + if (__n == 0) + return NULL; + __asm__ __volatile__ + ("std\n\t" + "repne; scasb\n\t" + "je 1f\n\t" + "movl $1,%0\n" + "1:" + : "=D" (__res), "=&c" (__d0) + : "a" (__c), "0" (__s), "1" (__n)); + return __res - 1; +} +#endif + /* Return the length of S. */ #define _HAVE_STRING_ARCH_strlen 1 #ifndef _FORCE_INLINES |