TLA  Line data    Source code

       1                 : /*
       2                 :  * bsearch_arg.c: bsearch variant with a user-supplied pointer
       3                 :  *
       4                 :  * Copyright (c) 2021-2023, PostgreSQL Global Development Group
       5                 :  * Copyright (c) 1990 Regents of the University of California.
       6                 :  * All rights reserved.
       7                 :  *
       8                 :  * Redistribution and use in source and binary forms, with or without
       9                 :  * modification, are permitted provided that the following conditions
      10                 :  * are met:
      11                 :  * 1. Redistributions of source code must retain the above copyright
      12                 :  *    notice, this list of conditions and the following disclaimer.
      13                 :  * 2. Redistributions in binary form must reproduce the above copyright
      14                 :  *    notice, this list of conditions and the following disclaimer in the
      15                 :  *    documentation and/or other materials provided with the distribution.
      16                 :  * 3. [rescinded 22 July 1999]
      17                 :  * 4. Neither the name of the University nor the names of its contributors
      18                 :  *    may be used to endorse or promote products derived from this software
      19                 :  *    without specific prior written permission.
      20                 :  *
      21                 :  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
      22                 :  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
      23                 :  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
      24                 :  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
      25                 :  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
      26                 :  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
      27                 :  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
      28                 :  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
      29                 :  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
      30                 :  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
      31                 :  * SUCH DAMAGE.
      32                 :  *
      33                 :  * src/port/bsearch_arg.c
      34                 :  */
      35                 : 
      36                 : #include "c.h"
      37                 : 
      38                 : /*
      39                 :  * Perform a binary search.
      40                 :  *
      41                 :  * The code below is a bit sneaky.  After a comparison fails, we
      42                 :  * divide the work in half by moving either left or right. If lim
      43                 :  * is odd, moving left simply involves halving lim: e.g., when lim
      44                 :  * is 5 we look at item 2, so we change lim to 2 so that we will
      45                 :  * look at items 0 & 1.  If lim is even, the same applies.  If lim
      46                 :  * is odd, moving right again involves halving lim, this time moving
      47                 :  * the base up one item past p: e.g., when lim is 5 we change base
      48                 :  * to item 3 and make lim 2 so that we will look at items 3 and 4.
      49                 :  * If lim is even, however, we have to shrink it by one before
      50                 :  * halving: e.g., when lim is 4, we still looked at item 2, so we
      51                 :  * have to make lim 3, then halve, obtaining 1, so that we will only
      52                 :  * look at item 3.
      53                 :  */
      54                 : void *
      55 CBC     7943733 : bsearch_arg(const void *key, const void *base0,
      56                 :             size_t nmemb, size_t size,
      57                 :             int (*compar) (const void *, const void *, void *),
      58                 :             void *arg)
      59                 : {
      60         7943733 :     const char *base = (const char *) base0;
      61                 :     int         lim,
      62                 :                 cmp;
      63                 :     const void *p;
      64                 : 
      65        50875074 :     for (lim = nmemb; lim != 0; lim >>= 1)
      66                 :     {
      67        42955566 :         p = base + (lim >> 1) * size;
      68        42955566 :         cmp = (*compar) (key, p, arg);
      69        42955566 :         if (cmp == 0)
      70           24225 :             return (void *) p;
      71        42931341 :         if (cmp > 0)
      72                 :         {                       /* key > p: move right */
      73        42486237 :             base = (const char *) p + size;
      74        42486237 :             lim--;
      75                 :         }                       /* else move left */
      76                 :     }
      77         7919508 :     return (NULL);
      78                 : }