musl - musl - an implementation of the standard library for Linux-based systems

musl - an implementation of the standard library for Linux-based systems

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author	Fangrui Song <i@maskray.me>	2018年07月21日 17:34:00 -0700
committer	Rich Felker <dalias@aerifal.cx>	2018年07月23日 15:14:29 -0400
commit	3d8322c7ad659210a4c8770ef455ca729ce7f395 (patch)
tree	25de8d1283cf1945c34aa5ccf444c46846a846da /src/stdlib/bsearch.c
parent	f2c6dbe2442027ed8fe0fa869918e41f495534d8 (diff)
download	musl-3d8322c7ad659210a4c8770ef455ca729ce7f395.tar.gz

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.

Diffstat (limited to 'src/stdlib/bsearch.c')

-rw-r--r--

src/stdlib/bsearch.c

1 files changed, 6 insertions, 6 deletions

diff --git a/src/stdlib/bsearch.c b/src/stdlib/bsearch.c
index 61d89367..fe050ea3 100644
--- a/src/stdlib/bsearch.c
+++ b/src/stdlib/bsearch.c

@@ -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;

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