[Glacier] Move hashmap to a real hash implementation.

lib/glacier/CMakeLists.txt

@@ -4,6 +4,7 @@ set(glacier_files
   string/string_view.cpp
   string/str_format.cpp
   string/str_split.cpp
+  util/hash.cpp
   )
 
 add_library(glacier STATIC

lib/glacier/container/hash_map.h

@@ -7,35 +7,11 @@
 #include "glacier/container/pair.h"
 #include "glacier/status/error.h"
 #include "glacier/string/string.h"
+#include "glacier/util/hash.h"
 
 namespace glcr {
 
-template <typename T>
-struct HashFunc {
-  uint64_t operator()(const T&);
-};
-
-template <>
-struct HashFunc<uint64_t> {
-  uint64_t operator()(const uint64_t& value) {
-    // FIXME: Write a real hash function.
-    return 0xABBAABBAABBAABBA ^ value;
-  }
-};
-
-template <>
-struct HashFunc<String> {
-  uint64_t operator()(const String& value) {
-    // FIXME: Write a real hash function.
-    uint64_t acc = 0;
-    for (uint64_t i = 0; i < value.length(); i++) {
-      acc += value[i];
-    }
-    return 0xABBAABBAABBAABBA ^ acc;
-  }
-};
-
-template <typename K, typename V, class H = HashFunc<K>>
+template <typename K, typename V, class H = Hash<K>>
 class HashMap {
  public:
   HashMap() = default;

lib/glacier/util/hash.cpp

@@ -0,0 +1,30 @@
+#include "util/hash.h"
+
+#include "string/string.h"
+
+namespace glcr {
+namespace {
+
+const uint64_t kFnvOffset = 0xcbf29ce484222325;
+const uint64_t kFnvPrime = 0x100000001b3;
+
+}  // namespace
+
+uint64_t Hash<uint64_t>::operator()(const uint64_t& value) {
+  uint64_t hash = kFnvOffset;
+  for (uint8_t i = 0; i < 8; i++) {
+    hash *= kFnvPrime;
+    hash ^= (value >> (8 * i)) & 0xFF;
+  }
+  return hash;
+}
+uint64_t Hash<String>::operator()(const String& value) {
+  uint64_t hash = kFnvOffset;
+  for (uint8_t i = 0; i < value.length(); i++) {
+    hash *= kFnvPrime;
+    hash ^= value[i];
+  }
+  return hash;
+}
+
+}  // namespace glcr

lib/glacier/util/hash.h

@@ -0,0 +1,27 @@
+#pragma once
+
+#include <stdint.h>
+
+namespace glcr {
+
+// General purpose templated hash function.
+// Currently the template speciializations
+// implement FNV hashing:
+// https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function
+template <typename T>
+struct Hash {
+  uint64_t operator()(const T&);
+};
+
+template <>
+struct Hash<uint64_t> {
+  uint64_t operator()(const uint64_t&);
+};
+
+class String;
+template <>
+struct Hash<String> {
+  uint64_t operator()(const String&);
+};
+
+}  // namespace glcr