diff options
author | Jim Meyering <jim@meyering.net> | 1993-10-21 00:10:34 +0000 |
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committer | Jim Meyering <jim@meyering.net> | 1993-10-21 00:10:34 +0000 |
commit | 0f8257073af8038d7987792baf84949ac37778fd (patch) | |
tree | 23c313bacef1c1e04dd7f11c5deb7cd32c9a99b4 | |
parent | e9220f51174195df875c2a03126968615f00166e (diff) | |
download | coreutils-0f8257073af8038d7987792baf84949ac37778fd.tar.xz |
* memchr.c (memchr): Do the 32-bit assignment only if !LONG_64_BITS.
In the 64-bit assignment, be careful to cast the shift operand to
long.
Abort if sizeof (unsigned long) > 8.
-rw-r--r-- | lib/memchr.c | 64 |
1 files changed, 43 insertions, 21 deletions
diff --git a/lib/memchr.c b/lib/memchr.c index cb8d4a22a..749510636 100644 --- a/lib/memchr.c +++ b/lib/memchr.c @@ -1,4 +1,4 @@ -/* Copyright (C) 1991 Free Software Foundation, Inc. +/* Copyright (C) 1991, 1993 Free Software Foundation, Inc. Based on strlen implemention by Torbjorn Granlund (tege@sics.se), with help from Dan Sahlin (dan@sics.se) and commentary by Jim Blandy (jimb@ai.mit.edu); @@ -20,51 +20,63 @@ License along with the GNU C Library; see the file COPYING.LIB. If not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */ - - - /* Search no more than N bytes of S for C. */ char * -memchr(s, c, n) - unsigned char * s ; - int c ; +memchr (s, c, n) + unsigned char *s; + int c; unsigned n; { - unsigned char *char_ptr; - unsigned long int *longword_ptr; + const unsigned char *char_ptr; + const unsigned long int *longword_ptr; unsigned long int longword, magic_bits, charmask; c = (unsigned char) c; /* Handle the first few characters by reading one character at a time. - Do this until CHAR_PTR is aligned on a 4-byte border. */ - for (char_ptr = s; n > 0 && ((unsigned long int) char_ptr & 3) != 0; + Do this until CHAR_PTR is aligned on a longword boundary. */ + for (char_ptr = s; n > 0 && ((unsigned long int) char_ptr + & (sizeof (longword) - 1)) != 0; --n, ++char_ptr) if (*char_ptr == c) return (char *) 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 + 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. */ +#ifdef LONG_64_BITS + /* 64-bit version of the magic. */ + magic_bits = ((unsigned long int) 0x7efefefe << 32) | 0xfefefeff; +#else magic_bits = 0x7efefeff; +#endif /* LONG_64_BITS */ /* Set up a longword, each of whose bytes is C. */ charmask = c | (c << 8); charmask |= charmask << 16; +#ifdef LONG_64_BITS + charmask |= charmask << 32; +#endif /* LONG_64_BITS */ + 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 (n >= 4) + 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. @@ -104,11 +116,11 @@ memchr(s, c, n) /* Add MAGIC_BITS to LONGWORD. */ if ((((longword + magic_bits) - - /* Set those bits that were unchanged by the addition. */ + + /* Set those bits that were unchanged by the addition. */ ^ ~longword) - - /* Look at only the hole bits. If any of the hole bits + + /* 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) @@ -116,7 +128,7 @@ memchr(s, c, n) /* Which of the bytes was C? If none of them were, it was a misfire; continue the search. */ - unsigned char *cp = ( unsigned char *) (longword_ptr - 1); + const unsigned char *cp = (const unsigned char *) (longword_ptr - 1); if (cp[0] == c) return (char *) cp; @@ -126,12 +138,22 @@ memchr(s, c, n) return (char *) &cp[2]; if (cp[3] == c) return (char *) &cp[3]; +#ifdef LONG_64_BITS + if (cp[4] == c) + return (char *) &cp[4]; + if (cp[5] == c) + return (char *) &cp[5]; + if (cp[6] == c) + return (char *) &cp[6]; + if (cp[7] == c) + return (char *) &cp[7]; +#endif /* LONG_64_BITS */ } - n -= 4; + n -= sizeof (longword); } - char_ptr = ( unsigned char *) longword_ptr; + char_ptr = (const unsigned char *) longword_ptr; while (n-- > 0) { |