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bsearch_arg.c

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1/*

2 * bsearch_arg.c: bsearch variant with a user-supplied pointer

3 *

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 [rescinded 22 July 1999]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 */

54void *

55 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 const char *base = (const char *) base0;

61 size_t lim;

62 int cmp;

63 const void *p;

64

65 for (lim = nmemb; lim != 0; lim >>= 1)

66 {

67 p = base + (lim >> 1) * size;

68 cmp = (*compar) (key, p, arg);

69 if (cmp == 0)

70 return (void *) p;

71 if (cmp > 0)

72 { /* key > p: move right */

73 base = (const char *) p + size;

74 lim--;

75 } /* else move left */

76 }

77 return (NULL);

78}

bsearch_arg

void * bsearch_arg(const void *key, const void *base0, size_t nmemb, size_t size, int(*compar)(const void *, const void *, void *), void *arg)

Definition: bsearch_arg.c:55

c.h

sort-test.key

key

Definition: sort-test.py:19

arg

void * arg

Definition: pg_backup_utils.c:29

cmp

static int cmp(const chr *x, const chr *y, size_t len)

Definition: regc_locale.c:743

PostgreSQL Source Code: src/port/bsearch_arg.c Source File