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33 @deftypefn Supplemental void* bsearch (const void *@var{key}, const void *@var{base}, size_t @var{nmemb}, size_t @var{size}, int (*@var{compar})(const void *, const void *))
35 Performs a search over an array of @var{nmemb} elements pointed to by
36 @var{base} for a member that matches the object pointed to by @var{key}.
37 The size of each member is specified by @var{size}. The array contents
38 should be sorted in ascending order according to the @var{compar}
39 comparison function. This routine should take two arguments pointing to
40 the @var{key} and to an array member, in that order, and should return an
41 integer less than, equal to, or greater than zero if the @var{key} object
42 is respectively less than, matching, or greater than the array member.
50 #include <sys/types.h> /* size_t */
54 * Perform a binary search.
56 * The code below is a bit sneaky. After a comparison fails, we
57 * divide the work in half by moving either left or right. If lim
58 * is odd, moving left simply involves halving lim: e.g., when lim
59 * is 5 we look at item 2, so we change lim to 2 so that we will
60 * look at items 0 & 1. If lim is even, the same applies. If lim
61 * is odd, moving right again involes halving lim, this time moving
62 * the base up one item past p: e.g., when lim is 5 we change base
63 * to item 3 and make lim 2 so that we will look at items 3 and 4.
64 * If lim is even, however, we have to shrink it by one before
65 * halving: e.g., when lim is 4, we still looked at item 2, so we
66 * have to make lim 3, then halve, obtaining 1, so that we will only
70 bsearch (register const void *key
, const void *base0
,
71 size_t nmemb
, register size_t size
,
72 register int (*compar
)(const void *, const void *))
74 register const char *base
= (const char *) base0
;
75 register int lim
, cmp
;
76 register const void *p
;
78 for (lim
= nmemb
; lim
!= 0; lim
>>= 1) {
79 p
= base
+ (lim
>> 1) * size
;
80 cmp
= (*compar
)(key
, p
);
83 if (cmp
> 0) { /* key > p: move right */
84 base
= (const char *)p
+ size
;
86 } /* else move left */
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