Optimize bsearch() implementation for performance

Optimize the bsearch() function to improve binary search performance.
Although the code size grew by 8 bytes, the new implementation achieves
a 15% reduction in execution time on my x86 machine, according to the
bench-bsearch benchmark results.

Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Reviewed-by: Noah Goldstein <goldstein.w.n@gmail.com>
Reviewed-by: DJ Delorie <dj@redhat.com>

1 files changed, 9 insertions, 11 deletions

diff --git a/bits/stdlib-bsearch.h b/bits/stdlib-bsearch.h
index 540d718..57f060b 100644
--- a/bits/stdlib-bsearch.h
+++ b/bits/stdlib-bsearch.h
@@ -20,22 +20,14 @@ __extern_inline void *
 bsearch (const void *__key, const void *__base, size_t __nmemb, size_t __size,
 	 __compar_fn_t __compar)
 {
-  size_t __l, __u, __idx;
   const void *__p;
   int __comparison;
 
-  __l = 0;
-  __u = __nmemb;
-  while (__l < __u)
+  while (__nmemb)
     {
-      __idx = (__l + __u) / 2;
-      __p = (const void *) (((const char *) __base) + (__idx * __size));
+      __p = (const void *) (((const char *) __base) + ((__nmemb >> 1) * __size));
       __comparison = (*__compar) (__key, __p);
-      if (__comparison < 0)
-	__u = __idx;
-      else if (__comparison > 0)
-	__l = __idx + 1;
-      else
+      if (__comparison == 0)
 	{
 #if __GNUC_PREREQ(4, 6)
 # pragma GCC diagnostic push
@@ -46,6 +38,12 @@ bsearch (const void *__key, const void *__base, size_t __nmemb, size_t __size,
 # pragma GCC diagnostic pop
 #endif
 	}
+      if (__comparison > 0)
+	{
+	  __base = ((const char *) __p) + __size;
+	  --__nmemb;
+	}
+      __nmemb >>= 1;
     }
 
   return NULL;