diff mbox series

[v4,2/2] Optimize bsearch() implementation for performance

Message ID 20240904160140.2743366-3-visitorckw@gmail.com
State New
Headers show
Series Optimization and benchmarking of bsearch() | expand

Commit Message

Kuan-Wei Chiu Sept. 4, 2024, 4:01 p.m. UTC 
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
benchmark results.

code size:
* old:
   text    data     bss     dec     hex filename
    250       0       0     250      fa ./stdlib/bsearch.o
* new:
   text    data     bss     dec     hex filename
    258       0       0     258     102 ./stdlib/bsearch.o

benchmark:
* old:
{
 "timing_type": "hp_timing",
 "functions": {
  "bsearch": {
   "bench-variant": "default",
   "array-size": 100000,
   "key-pattern": "ascending",
   "contained": "yes",
   "results": [121.735]
  }
 }
}
* new:
{
 "timing_type": "hp_timing",
 "functions": {
  "bsearch": {
   "bench-variant": "default",
   "array-size": 100000,
   "key-pattern": "ascending",
   "contained": "yes",
   "results": [103.063]
  }
 }
}

Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Reviewed-by: Noah Goldstein <goldstein.w.n@gmail.com>
---
Changes in v4:
- Update the benchmark result format in commit messages.

 bits/stdlib-bsearch.h | 20 +++++++++-----------
 1 file changed, 9 insertions(+), 11 deletions(-)
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Patch

diff --git a/bits/stdlib-bsearch.h b/bits/stdlib-bsearch.h
index 540d718952..57f060b504 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;