benchtests: Add benchmark test for bsearch

Introduce a benchmark test for the bsearch function to evaluate its
performance.

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>

benchtests/Makefile

@@ -266,6 +266,7 @@ hash-benchset := \
 
 stdlib-benchset := \
   arc4random \
+  bsearch \
   random-lock \
   strtod \
   # stdlib-benchset

benchtests/bench-bsearch.c

@@ -0,0 +1,137 @@
+/* Measure bsearch functions.
+   Copyright (C) 2022-2024 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#define TEST_MAIN
+#define TEST_NAME "bsearch"
+
+#define ARRAY_SIZE 100000
+#define LOOP_ITERS 100000000
+
+/* Directly including <stdlib.h> leads to the use of an inline version
+   of bsearch(), which may cause our test cases to be optimized away by
+   the compiler due to predictability. To address this, we should
+   include <bits/stdlib-bsearch.h> directly and replace __extern_inline
+   with __attribute__((noinline)) to ensure the compiler does not
+   inline the function. Additionally, we need to add some macros
+   required for compilation. */
+#include <stddef.h>
+#define __extern_inline __attribute__((noinline))
+#define __GNUC_PREREQ(x, y) 0
+typedef int (*__compar_fn_t) (const void *, const void *);
+#include <bits/stdlib-bsearch.h>
+#undef __extern_inline
+#undef __GNUC_PREREQ
+
+#include "json-lib.h"
+#include "bench-timing.h"
+
+int arr[ARRAY_SIZE];
+
+static int
+comp_asc (const void *p1, const void *p2)
+{
+  int x1 = *(int *) p1;
+  int x2 = *(int *) p2;
+
+  if (x1 < x2)
+    return -1;
+  if (x1 > x2)
+    return 1;
+  return 0;
+}
+
+static int
+comp_desc (const void *p1, const void *p2)
+{
+  int x1 = *(int *) p1;
+  int x2 = *(int *) p2;
+
+  if (x1 > x2)
+    return -1;
+  if (x1 < x2)
+    return 1;
+  return 0;
+}
+
+static void
+do_bench (json_ctx_t *json_ctx, bool ascending, bool contained)
+{
+  size_t i, iters = LOOP_ITERS;
+  timing_t start, stop, cur;
+  int key;
+  volatile __attribute__((__unused__)) void *res;
+
+  for (i = 0; i < ARRAY_SIZE; ++i)
+    {
+      arr[i] = (ascending ? i : ARRAY_SIZE - 1 - i) << 1;
+    }
+
+  json_element_object_begin (json_ctx);
+  json_attr_uint (json_ctx, "array-size", ARRAY_SIZE);
+  json_attr_uint (json_ctx, "element-size", sizeof(arr[0]));
+  json_attr_string (json_ctx, "key-pattern", ascending ? "ascending" : "descending");
+  json_attr_string (json_ctx, "contained", contained ? "yes" : "no");
+  json_attr_string (json_ctx, "simple", "yes");
+
+  TIMING_NOW (start);
+
+  for (i = 0; i < iters; ++i)
+    {
+      key = (i % ARRAY_SIZE << 1) + !contained;
+      res = bsearch(&key, arr, ARRAY_SIZE, sizeof(arr[0]), ascending ? comp_asc : comp_desc);
+    }
+
+  TIMING_NOW (stop);
+
+  TIMING_DIFF (cur, start, stop);
+
+  json_attr_double (json_ctx, "timing", (double) cur / (double) iters);
+  json_element_object_end (json_ctx);
+}
+
+int
+do_test (void)
+{
+  json_ctx_t json_ctx;
+
+  json_init (&json_ctx, 0, stdout);
+
+  json_document_begin (&json_ctx);
+  json_attr_string (&json_ctx, "timing_type", TIMING_TYPE);
+  json_attr_object_begin (&json_ctx, "functions");
+  json_attr_object_begin (&json_ctx, TEST_NAME);
+  json_attr_string (&json_ctx, "bench-variant", "default");
+  json_array_begin (&json_ctx, "results");
+
+  for (int ascending = 0; ascending < 2; ++ascending)
+    {
+      for (int contained = 0; contained < 2; ++contained)
+        {
+          do_bench(&json_ctx, ascending, contained);
+        }
+    }
+
+  json_array_end (&json_ctx);
+  json_attr_object_end (&json_ctx);
+  json_attr_object_end (&json_ctx);
+  json_document_end (&json_ctx);
+
+  return 0;
+}
+
+#include <support/test-driver.c>