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Diffstat (limited to 'librols/findbytes.c')
| -rw-r--r-- | librols/findbytes.c | 164 |
1 files changed, 164 insertions, 0 deletions
diff --git a/librols/findbytes.c b/librols/findbytes.c new file mode 100644 index 0000000..0b56597 --- /dev/null +++ b/librols/findbytes.c @@ -0,0 +1,164 @@ +/* + * This file has been modified for the cdrkit suite. + * + * The behaviour and appearence of the program code below can differ to a major + * extent from the version distributed by the original author(s). + * + * For details, see Changelog file distributed with the cdrkit package. If you + * received this file from another source then ask the distributing person for + * a log of modifications. + * + */ + +/* @(#)findbytes.c 1.2 03/06/15 Copyright 2000-2003 J. Schilling */ +/* + * Find a byte with specific value in memory. + * + * Copyright (c) 2000-2003 J. Schilling + * + * Based on a strlen() idea from Torbjorn Granlund (tege@sics.se) and + * Dan Sahlin (dan@sics.se) and the memchr() suggestion + * from Dick Karpinski (dick@cca.ucsf.edu). + */ +/* + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 + * as published by the Free Software Foundation. + * + * This program 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 General Public License for more details. + * + * You should have received a copy of the GNU General Public License along with + * this program; see the file COPYING. If not, write to the Free Software + * Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. + */ + +#include <mconfig.h> +#include <stdxlib.h> +#include <utypes.h> +#include <align.h> +#include <standard.h> +#include <strdefs.h> +#include <schily.h> + +#ifdef PROTOTYPES +EXPORT char * +findbytes(const void *vp, int cnt, char val) +#else +EXPORT char * +findbytes(vp, cnt, val) + const void *vp; + register int cnt; + char val; +#endif +{ + register Uchar uval = (Uchar)val; + register const Uchar *cp = (Uchar *)vp; + register const Ulong *lp; + register Ulong lval; + register Ulong lmask; + register Ulong magic_mask; + + /* + * Test byte-wise until cp is properly aligned for a long pointer. + */ + while (--cnt >= 0 && !laligned(cp)) { + if (*cp++ == uval) + return ((char *)--cp); + } + cnt++; + + /* + * The magic mask is a long word where all carry bits a clear. + * This are bits 8, 16, 24 ... + * In addition, the top bit is not set (e.g bit 31 or 63). The magic + * mask will look this way: + * + * bits: 01111110 11111110 ... 11111110 11111111 + * bytes: AAAAAAAA BBBBBBBB ... CCCCCCCC DDDDDDDD + * + * If we add anything to this magic number, no carry bit will change if + * it is the first carry bit left to a 0 byte. Adding anything != 0 + * to the magic number will just turn the carry bit left to the byte + * but does not propagate any further. + */ +#if SIZE_LONG == 4 + magic_mask = 0x7EFEFEFFL; +#else +#if SIZE_LONG == 8 + magic_mask = 0x7EFEFEFEFEFEFEFFL; +#else + /* + * #error will not work for all compilers (e.g. sunos4) + * The following line will abort compilation on all compilers + * if none of the above is defines. And that's what we want. + */ + error SIZE_LONG has unknown value +#endif +#endif + + lmask = val & 0xFF; + lmask |= lmask << 8; + lmask |= lmask << 16; +#if SIZE_LONG > 4 + lmask |= lmask << 32; +#endif +#if SIZE_LONG > 8 + error SIZE_LONG has unknown value +#endif + for (lp = (const Ulong *)cp; cnt >= sizeof (long); cnt -= sizeof (long)) { + /* + * We are not looking for 0 bytes so we need to xor with the + * long mask of repeated bytes. If any of the bytes matches our + * wanted char, we will create a 0 byte in the current long. + * But how will we find if at least one byte in a long is zero? + * + * If we add 'magic_mask' and any of the holes in the magic + * mask do not change, we most likely found a 0 byte in the + * long word. It is only a most likely match because if bits + * 24..30 (ot bits 56..62) are 0 but bit 31 (or bit 63) is set + * we will believe that we found a match but there is none. + * This will happen if there is 0x80nnnnnn / 0x80nnnnnnnnnnnnnn + */ + lval = (*lp++ ^ lmask); /* create 0 byte on match */ + lval = (lval + magic_mask) ^ ~lval; /* set bits unchanged by +*/ + if ((lval & ~magic_mask) != 0) { /* a magic hole was set */ + /* + * If any of the hole bits did not change by addition, + * we most likely had a match. + * If this was a correct match, find the matching byte. + */ + cp = (const Uchar *)(lp - 1); + + if (cp[0] == uval) + return ((char *)cp); + if (cp[1] == uval) + return ((char *)&cp[1]); + if (cp[2] == uval) + return ((char *)&cp[2]); + if (cp[3] == uval) + return ((char *)&cp[3]); +#if SIZE_LONG > 4 + if (cp[4] == uval) + return ((char *)&cp[4]); + if (cp[5] == uval) + return ((char *)&cp[5]); + if (cp[6] == uval) + return ((char *)&cp[6]); + if (cp[7] == uval) + return ((char *)&cp[7]); +#endif +#if SIZE_LONG > 8 + error SIZE_LONG has unknown value +#endif + } + } + + for (cp = (const Uchar *)lp; --cnt >= 0; ) { + if (*cp++ == uval) + return ((char *)--cp); + } + return ((char *)NULL); +} |