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bsearch: simplify and optimize 

maintainer's note: the key observation here is that the compared
element is the first slot of the second ceil(half) of the array, and
thus can be removed for further comparison when it does not match, so
that we descend into the second ceil(half)-1 rather than ceil(half)
elements. this change ensures that nel strictly decreases with each
iteration, so that the case of != but nel==1 does not need to be
special-cased anymore.
This commit is contained in:
Fangrui Song 2018-07-21 17:34:00 -07:00 committed by Rich Felker
parent f2c6dbe244
commit 3d8322c7ad
1 changed files with 6 additions and 6 deletions
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12
src/stdlib/bsearch.c
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@ -7,13 +7,13 @@ void *bsearch(const void *key, const void *base, size_t nel, size_t width, int (
while (nel > 0) {
try = (char *)base + width*(nel/2);
sign = cmp(key, try);
if (!sign) return try;
else if (nel == 1) break;
else if (sign < 0)
if (sign < 0) {
nel /= 2;
else {
base = try;
nel -= nel/2;
} else if (sign > 0) {
base = (char *)try + width;
nel -= nel/2+1;
} else {
return try;
}
}
return NULL;