add hash utility, and support for hashing and comparing expressions

1 files changed, 39 insertions, 0 deletions

diff --git a/src/support/hash.h b/src/support/hash.h
new file mode 100644
index 000000000..e2d393d25
--- /dev/null
+++ b/src/support/hash.h
@@ -0,0 +1,39 @@
+/*
+ * Copyright 2015 WebAssembly Community Group participants
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef wasm_support_hash_h
+#define wasm_support_hash_h
+
+#include <stdint.h>
+
+namespace wasm {
+
+inline uint32_t rehash(uint32_t x, uint32_t y) { // see http://www.cse.yorku.ca/~oz/hash.html
+  uint32_t hash = 5381;
+  while (x) {
+    hash = ((hash << 5) + hash) ^ (x & 0xff);
+    x >>= 8;
+  }
+  while (y) {
+    hash = ((hash << 5) + hash) ^ (y & 0xff);
+    y >>= 8;
+  }
+  return hash;
+}
+
+} // namespace wasm
+
+#endif // wasm_support_hash_h