optional support for doing perfect hashing of feature strings to save lots of memory

1 files changed, 37 insertions, 0 deletions

diff --git a/utils/perfect_hash.cc b/utils/perfect_hash.cc
new file mode 100644
index 00000000..706e2741
--- /dev/null
+++ b/utils/perfect_hash.cc
@@ -0,0 +1,37 @@
+#include "config.h"
+
+#ifdef HAVE_CMPH
+
+#include "perfect_hash.h"
+
+#include <cstdio>
+#include <iostream>
+
+using namespace std;
+
+PerfectHashFunction::~PerfectHashFunction() {
+  cmph_destroy(mphf_);
+}
+
+PerfectHashFunction::PerfectHashFunction(const string& fname) {
+  FILE* f = fopen(fname.c_str(), "r");
+  if (!f) {
+    cerr << "Failed to open file " << fname << " for reading: cannot load hash function.\n";
+    abort();
+  }
+  mphf_ = cmph_load(f);
+  if (!mphf_) {
+    cerr << "cmph_load failed on " << fname << "!\n";
+    abort();
+  }
+}
+
+size_t PerfectHashFunction::operator()(const string& key) const {
+  return cmph_search(mphf_, &key[0], key.size());
+}
+
+size_t PerfectHashFunction::number_of_keys() const {
+  return cmph_size(mphf_);
+}
+
+#endif