Mercurial > hg > octave-kai > gnulib-hg
annotate lib/memchr.c @ 2932:e422838277f4
Update from libc.
Adjust for portability:
[HAVE_STDLIB_H]: Include stdlib.h.
[HAVE_BP_SYM_H || _LIBC]: Guard inclusion of bp-sym.h.
Undef __memchr, too.
[!weak_alias]: Define __memchr to memchr.
| author | Jim Meyering <jim@meyering.net> |
|---|---|
| date | Sat, 28 Oct 2000 08:22:11 +0000 |
| parents | 807294ed0f4f |
| children | 42147e1c0cee |
| rev | line source |
|---|---|
| 2932 | 1 /* Copyright (C) 1991,93,96,97,99,2000 Free Software Foundation, Inc. |
| 884 | 2 Based on strlen implementation by Torbjorn Granlund (tege@sics.se), |
| 14 | 3 with help from Dan Sahlin (dan@sics.se) and |
| 4 commentary by Jim Blandy (jimb@ai.mit.edu); | |
| 5 adaptation to memchr suggested by Dick Karpinski (dick@cca.ucsf.edu), | |
| 6 and implemented by Roland McGrath (roland@ai.mit.edu). | |
| 7 | |
| 394 | 8 NOTE: The canonical source of this file is maintained with the GNU C Library. |
| 9 Bugs can be reported to bug-glibc@prep.ai.mit.edu. | |
| 14 | 10 |
| 394 | 11 This program is free software; you can redistribute it and/or modify it |
| 12 under the terms of the GNU General Public License as published by the | |
| 13 Free Software Foundation; either version 2, or (at your option) any | |
| 14 later version. | |
| 15 | |
| 16 This program is distributed in the hope that it will be useful, | |
| 14 | 17 but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 394 | 18 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 19 GNU General Public License for more details. | |
| 14 | 20 |
| 394 | 21 You should have received a copy of the GNU General Public License |
| 22 along with this program; if not, write to the Free Software | |
|
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23 Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, |
|
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24 USA. */ |
| 14 | 25 |
| 166 | 26 #ifdef HAVE_CONFIG_H |
| 1872 | 27 # include <config.h> |
| 166 | 28 #endif |
| 29 | |
| 394 | 30 #undef __ptr_t |
| 31 #if defined (__cplusplus) || (defined (__STDC__) && __STDC__) | |
| 32 # define __ptr_t void * | |
| 33 #else /* Not C++ or ANSI C. */ | |
| 34 # define __ptr_t char * | |
| 35 #endif /* C++ or ANSI C. */ | |
| 36 | |
| 2932 | 37 #if defined _LIBC |
| 448 | 38 # include <string.h> |
| 2932 | 39 # include <memcopy.h> |
| 40 #else | |
| 41 # define reg_char char | |
| 448 | 42 #endif |
| 43 | |
| 2932 | 44 #if HAVE_STDLIB_H || defined _LIBC |
| 45 # include <stdlib.h> | |
| 46 #endif | |
| 47 | |
| 48 #if HAVE_LIMITS_H || defined _LIBC | |
| 443 | 49 # include <limits.h> |
| 394 | 50 #endif |
| 51 | |
| 52 #define LONG_MAX_32_BITS 2147483647 | |
| 53 | |
| 54 #ifndef LONG_MAX | |
| 1872 | 55 # define LONG_MAX LONG_MAX_32_BITS |
| 394 | 56 #endif |
| 57 | |
| 58 #include <sys/types.h> | |
| 2932 | 59 #if HAVE_BP_SYM_H || defined _LIBC |
| 60 # include <bp-sym.h> | |
| 61 #else | |
| 62 # define BP_SYM(sym) sym | |
| 63 #endif | |
| 394 | 64 |
| 2932 | 65 #undef memchr |
| 66 #undef __memchr | |
| 394 | 67 |
| 14 | 68 /* Search no more than N bytes of S for C. */ |
| 394 | 69 __ptr_t |
| 2932 | 70 __memchr (s, c_in, n) |
| 394 | 71 const __ptr_t s; |
| 2932 | 72 int c_in; |
| 394 | 73 size_t n; |
| 14 | 74 { |
|
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75 const unsigned char *char_ptr; |
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76 const unsigned long int *longword_ptr; |
| 14 | 77 unsigned long int longword, magic_bits, charmask; |
| 2932 | 78 unsigned reg_char c; |
| 14 | 79 |
| 2932 | 80 c = (unsigned char) c_in; |
| 14 | 81 |
| 82 /* Handle the first few characters by reading one character at a time. | |
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83 Do this until CHAR_PTR is aligned on a longword boundary. */ |
| 448 | 84 for (char_ptr = (const unsigned char *) s; |
| 85 n > 0 && ((unsigned long int) char_ptr | |
| 86 & (sizeof (longword) - 1)) != 0; | |
| 14 | 87 --n, ++char_ptr) |
| 88 if (*char_ptr == c) | |
| 394 | 89 return (__ptr_t) char_ptr; |
| 14 | 90 |
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91 /* All these elucidatory comments refer to 4-byte longwords, |
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92 but the theory applies equally well to 8-byte longwords. */ |
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93 |
| 14 | 94 longword_ptr = (unsigned long int *) char_ptr; |
| 95 | |
| 96 /* Bits 31, 24, 16, and 8 of this number are zero. Call these bits | |
| 97 the "holes." Note that there is a hole just to the left of | |
| 98 each byte, with an extra at the end: | |
| 448 | 99 |
| 14 | 100 bits: 01111110 11111110 11111110 11111111 |
| 448 | 101 bytes: AAAAAAAA BBBBBBBB CCCCCCCC DDDDDDDD |
| 14 | 102 |
| 103 The 1-bits make sure that carries propagate to the next 0-bit. | |
| 104 The 0-bits provide holes for carries to fall into. */ | |
| 394 | 105 |
| 106 if (sizeof (longword) != 4 && sizeof (longword) != 8) | |
| 107 abort (); | |
| 108 | |
| 109 #if LONG_MAX <= LONG_MAX_32_BITS | |
| 110 magic_bits = 0x7efefeff; | |
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111 #else |
| 394 | 112 magic_bits = ((unsigned long int) 0x7efefefe << 32) | 0xfefefeff; |
| 113 #endif | |
| 14 | 114 |
| 115 /* Set up a longword, each of whose bytes is C. */ | |
| 116 charmask = c | (c << 8); | |
| 117 charmask |= charmask << 16; | |
| 394 | 118 #if LONG_MAX > LONG_MAX_32_BITS |
| 400 | 119 charmask |= charmask << 32; |
| 394 | 120 #endif |
| 14 | 121 |
| 122 /* Instead of the traditional loop which tests each character, | |
| 123 we will test a longword at a time. The tricky part is testing | |
| 124 if *any of the four* bytes in the longword in question are zero. */ | |
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125 while (n >= sizeof (longword)) |
| 14 | 126 { |
| 127 /* We tentatively exit the loop if adding MAGIC_BITS to | |
| 128 LONGWORD fails to change any of the hole bits of LONGWORD. | |
| 129 | |
| 130 1) Is this safe? Will it catch all the zero bytes? | |
| 131 Suppose there is a byte with all zeros. Any carry bits | |
| 132 propagating from its left will fall into the hole at its | |
| 133 least significant bit and stop. Since there will be no | |
| 134 carry from its most significant bit, the LSB of the | |
| 135 byte to the left will be unchanged, and the zero will be | |
| 136 detected. | |
| 137 | |
| 138 2) Is this worthwhile? Will it ignore everything except | |
| 139 zero bytes? Suppose every byte of LONGWORD has a bit set | |
| 140 somewhere. There will be a carry into bit 8. If bit 8 | |
| 141 is set, this will carry into bit 16. If bit 8 is clear, | |
| 142 one of bits 9-15 must be set, so there will be a carry | |
| 143 into bit 16. Similarly, there will be a carry into bit | |
| 144 24. If one of bits 24-30 is set, there will be a carry | |
| 145 into bit 31, so all of the hole bits will be changed. | |
| 146 | |
| 147 The one misfire occurs when bits 24-30 are clear and bit | |
| 148 31 is set; in this case, the hole at bit 31 is not | |
| 149 changed. If we had access to the processor carry flag, | |
| 150 we could close this loophole by putting the fourth hole | |
| 151 at bit 32! | |
| 152 | |
| 153 So it ignores everything except 128's, when they're aligned | |
| 154 properly. | |
| 155 | |
| 156 3) But wait! Aren't we looking for C, not zero? | |
| 157 Good point. So what we do is XOR LONGWORD with a longword, | |
| 158 each of whose bytes is C. This turns each byte that is C | |
| 159 into a zero. */ | |
| 160 | |
| 161 longword = *longword_ptr++ ^ charmask; | |
| 162 | |
| 163 /* Add MAGIC_BITS to LONGWORD. */ | |
| 164 if ((((longword + magic_bits) | |
| 448 | 165 |
| 394 | 166 /* Set those bits that were unchanged by the addition. */ |
| 14 | 167 ^ ~longword) |
| 448 | 168 |
| 394 | 169 /* Look at only the hole bits. If any of the hole bits |
| 14 | 170 are unchanged, most likely one of the bytes was a |
| 171 zero. */ | |
| 172 & ~magic_bits) != 0) | |
| 173 { | |
| 174 /* Which of the bytes was C? If none of them were, it was | |
| 175 a misfire; continue the search. */ | |
| 176 | |
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177 const unsigned char *cp = (const unsigned char *) (longword_ptr - 1); |
| 14 | 178 |
| 179 if (cp[0] == c) | |
| 394 | 180 return (__ptr_t) cp; |
| 14 | 181 if (cp[1] == c) |
| 394 | 182 return (__ptr_t) &cp[1]; |
| 14 | 183 if (cp[2] == c) |
| 394 | 184 return (__ptr_t) &cp[2]; |
| 14 | 185 if (cp[3] == c) |
| 394 | 186 return (__ptr_t) &cp[3]; |
| 187 #if LONG_MAX > 2147483647 | |
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188 if (cp[4] == c) |
| 394 | 189 return (__ptr_t) &cp[4]; |
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190 if (cp[5] == c) |
| 394 | 191 return (__ptr_t) &cp[5]; |
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192 if (cp[6] == c) |
| 394 | 193 return (__ptr_t) &cp[6]; |
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194 if (cp[7] == c) |
| 394 | 195 return (__ptr_t) &cp[7]; |
| 196 #endif | |
| 14 | 197 } |
| 198 | |
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199 n -= sizeof (longword); |
| 14 | 200 } |
| 201 | |
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202 char_ptr = (const unsigned char *) longword_ptr; |
| 14 | 203 |
| 204 while (n-- > 0) | |
| 205 { | |
| 206 if (*char_ptr == c) | |
| 394 | 207 return (__ptr_t) char_ptr; |
| 14 | 208 else |
| 209 ++char_ptr; | |
| 210 } | |
| 211 | |
| 212 return 0; | |
| 213 } | |
| 2932 | 214 #ifdef weak_alias |
| 215 weak_alias (__memchr, BP_SYM (memchr)) | |
| 216 #endif |