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gcc.gnu.org Git - gcc.git/blob - libiberty/bsearch.c
2 * Copyright (c) 1990 Regents of the University of California.
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6 * modification, are permitted provided that the following conditions
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9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
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12 * documentation and/or other materials provided with the distribution.
13 * 3. [rescinded 22 July 1999]
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33 #include <sys/types.h> /* size_t */
37 * Perform a binary search.
39 * The code below is a bit sneaky. After a comparison fails, we
40 * divide the work in half by moving either left or right. If lim
41 * is odd, moving left simply involves halving lim: e.g., when lim
42 * is 5 we look at item 2, so we change lim to 2 so that we will
43 * look at items 0 & 1. If lim is even, the same applies. If lim
44 * is odd, moving right again involes halving lim, this time moving
45 * the base up one item past p: e.g., when lim is 5 we change base
46 * to item 3 and make lim 2 so that we will look at items 3 and 4.
47 * If lim is even, however, we have to shrink it by one before
48 * halving: e.g., when lim is 4, we still looked at item 2, so we
49 * have to make lim 3, then halve, obtaining 1, so that we will only
53 bsearch(key
, base0
, nmemb
, size
, compar
)
58 register int (*compar
)();
60 register char *base
= base0
;
61 register int lim
, cmp
;
64 for (lim
= nmemb
; lim
!= 0; lim
>>= 1) {
65 p
= base
+ (lim
>> 1) * size
;
66 cmp
= (*compar
)(key
, p
);
69 if (cmp
> 0) { /* key > p: move right */
70 base
= (char *)p
+ size
;
72 } /* else move left */
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