The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/libkern/strspn.c

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    1 /*-
    2  * Copyright (c) 2005 David Schultz <das@FreeBSD.ORG>
    3  * All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice, this list of conditions and the following disclaimer.
   10  * 2. Redistributions in binary form must reproduce the above copyright
   11  *    notice, this list of conditions and the following disclaimer in the
   12  *    documentation and/or other materials provided with the distribution.
   13  *
   14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   24  * SUCH DAMAGE.
   25  */
   26 
   27 #include <sys/cdefs.h>
   28 __FBSDID("$FreeBSD: releng/7.4/sys/libkern/strspn.c 144545 2005-04-02 18:52:44Z das $");
   29 
   30 #include <sys/libkern.h>
   31 #include <sys/limits.h>
   32 #include <sys/types.h>
   33 
   34 #define IDX(c)  ((u_char)(c) / LONG_BIT)
   35 #define BIT(c)  ((u_long)1 << ((u_char)(c) % LONG_BIT))
   36 
   37 size_t
   38 strspn(const char *s, const char *charset)
   39 {
   40         /*
   41          * NB: idx and bit are temporaries whose use causes gcc 3.4.2 to
   42          * generate better code.  Without them, gcc gets a little confused.
   43          */
   44         const char *s1;
   45         u_long bit;
   46         u_long tbl[(UCHAR_MAX + 1) / LONG_BIT];
   47         int idx;
   48 
   49         if(*s == '\0')
   50                 return (0);
   51 
   52 #if LONG_BIT == 64      /* always better to unroll on 64-bit architectures */
   53         tbl[3] = tbl[2] = tbl[1] = tbl[0] = 0;
   54 #else
   55         for (idx = 0; idx < sizeof(tbl) / sizeof(tbl[0]); idx++)
   56                 tbl[idx] = 0;
   57 #endif
   58         for (; *charset != '\0'; charset++) {
   59                 idx = IDX(*charset);
   60                 bit = BIT(*charset);
   61                 tbl[idx] |= bit;
   62         }
   63 
   64         for(s1 = s; ; s1++) {
   65                 idx = IDX(*s1);
   66                 bit = BIT(*s1);
   67                 if ((tbl[idx] & bit) == 0)
   68                         break;
   69         }
   70         return (s1 - s);
   71 }

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