Initial OpenType Font Variations Support

third_party/WebKit/Source/platform/fonts/opentype/FontSettings.cpp

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "platform/fonts/opentype/FontSettings.h"
+
+#include "wtf/StringHasher.h"
+#include "wtf/text/AtomicStringHash.h"
+#include "wtf/text/StringHash.h"
+
+namespace blink {
+
+uint32_t atomicStringToFourByteTag(AtomicString tag) {
+  DCHECK_EQ(tag.length(), 4u);
+  return (((tag[0]) << 24) | ((tag[1]) << 16) | ((tag[2]) << 8) | (tag[3]));
+}
+
+static inline void addToHash(unsigned& hash, unsigned key) {
+  hash = ((hash << 5) + hash) + key;  // Djb2
+};
+
+static inline void addFloatToHash(unsigned& hash, float value) {
+  addToHash(hash, StringHasher::hashMemory(&value, sizeof(value)));

[kojii, 2016/12/21 14:53:12]

Not important but just from curiosity, why don't we use DefaultHash<float>?

[drott, 2016/12/21 15:22:00]

Good point, took this from similar code in FontDescription or FontCacheKey and
could have update this. Changed to FloatHash<float>.

+};
+
+unsigned FontVariationSettings::hash() const {
+  unsigned computedHash = size() ? 5381 : 0;
+  unsigned numFeatures = size();
+  for (unsigned i = 0; i < numFeatures; ++i) {
+    StringHasher stringHasher;
+    const AtomicString& tag = at(i).tag();
+    for (unsigned j = 0; j < tag.length(); j++) {
+      stringHasher.addCharacter(tag[j]);
+    }
+    addToHash(computedHash, stringHasher.hash());
+    addFloatToHash(computedHash, at(i).value());
+  }
+  return computedHash;
+}
+
+}  // namespace blink