Line data    Source code

       1             : /*
       2             :  * bsearch_arg.c: bsearch variant with a user-supplied pointer
       3             :  *
       4             :  * Copyright (c) 2021-2024, 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 [rescinded 22 July 1999]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      106686 : 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      106686 :     const char *base = (const char *) base0;
      61             :     size_t      lim;
      62             :     int         cmp;
      63             :     const void *p;
      64             : 
      65      633408 :     for (lim = nmemb; lim != 0; lim >>= 1)
      66             :     {
      67      575316 :         p = base + (lim >> 1) * size;
      68      575316 :         cmp = (*compar) (key, p, arg);
      69      575316 :         if (cmp == 0)
      70       48594 :             return (void *) p;
      71      526722 :         if (cmp > 0)
      72             :         {                       /* key > p: move right */
      73      418668 :             base = (const char *) p + size;
      74      418668 :             lim--;
      75             :         }                       /* else move left */
      76             :     }
      77       58092 :     return (NULL);
      78             : }