Add a hash collision benchmark.

1 files changed, 43 insertions, 0 deletions

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);
+}