From d59e82c4a098f4e3987871fae0fbd6347b64b1f2 Mon Sep 17 00:00:00 2001
From: Nico Weber <nicolasweber@gmx.de>
Date: Fri, 15 Jun 2012 09:50:06 -0700
Subject: Add a hash collision benchmark.

---
 configure.py                | 21 ++++++++++-----------
 src/hash_collision_bench.cc | 43 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+), 11 deletions(-)
 create mode 100644 src/hash_collision_bench.cc

diff --git a/configure.py b/configure.py
index 7839dae..9eb2a48 100755
--- a/configure.py
+++ b/configure.py
@@ -314,21 +314,20 @@ n.newline()
 all_targets += ninja_test
 
 
-n.comment('Perftest executables.')
+n.comment('Ancilliary executables.')
 objs = cxx('parser_perftest')
-parser_perftest = n.build(binary('parser_perftest'), 'link', objs,
-                          implicit=ninja_lib,
-                          variables=[('libs', libs)])
+all_targets += n.build(binary('parser_perftest'), 'link', objs,
+                       implicit=ninja_lib, variables=[('libs', libs)])
 objs = cxx('build_log_perftest')
-build_log_perftest = n.build(binary('build_log_perftest'), 'link', objs,
-                             implicit=ninja_lib,
-                             variables=[('libs', libs)])
+all_targets += n.build(binary('build_log_perftest'), 'link', objs,
+                       implicit=ninja_lib, variables=[('libs', libs)])
 objs = cxx('canon_perftest')
-canon_perftest = n.build(binary('canon_perftest'), 'link', objs,
-                         implicit=ninja_lib,
-                         variables=[('libs', libs)])
+all_targets += n.build(binary('canon_perftest'), 'link', objs,
+                       implicit=ninja_lib, variables=[('libs', libs)])
+objs = cxx('hash_collision_bench')
+all_targets += n.build(binary('hash_collision_bench'), 'link', objs,
+                              implicit=ninja_lib, variables=[('libs', libs)])
 n.newline()
-all_targets += parser_perftest + build_log_perftest + canon_perftest
 
 n.comment('Generate a graph using the "graph" tool.')
 n.rule('gendot',
diff --git a/src/hash_collision_bench.cc b/src/hash_collision_bench.cc
new file mode 100644
index 0000000..d9b09d9
--- /dev/null
+++ b/src/hash_collision_bench.cc
@@ -0,0 +1,43 @@
+#include "build_log.h"
+
+int random(int low, int high) {
+  return int(low + (rand() / double(RAND_MAX)) * (high - low) + 0.5);
+}
+
+void RandomCommand(char** s) {
+  int len = random(5, 100);
+  *s = new char[len];
+  for (int i = 0; i < len; ++i)
+    (*s)[i] = random(32, 127);
+}
+
+int main() {
+  const int N = 20 * 1000 * 1000;
+
+  // Leak these, else 10% of the runtime is spent destroying strings.
+  char** commands = new char*[N];
+  pair<uint64_t, int>* hashes = new pair<uint64_t, int>[N];
+
+  srand(time(NULL));
+
+  for (int i = 0; i < N; ++i) {
+    RandomCommand(&commands[i]);
+    hashes[i] = make_pair(BuildLog::LogEntry::HashCommand(commands[i]), i);
+  }
+
+  sort(hashes, hashes + N);
+
+  int num_collisions = 0;
+  for (int i = 1; i < N; ++i) {
+    if (hashes[i - 1].first == hashes[i].first) {
+      if (strcmp(commands[hashes[i - 1].second],
+                 commands[hashes[i].second]) != 0) {
+        printf("collision!\n  string 1: '%s'\n  string 2: '%s'\n",
+               commands[hashes[i - 1].second],
+               commands[hashes[i].second]);
+        num_collisions++;
+      }
+    }
+  }
+  printf("\n\n%d collisions after %d runs\n", num_collisions, N);
+}
-- 
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