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-rw-r--r--modules/woff2/src/variable_length.cc137
1 files changed, 137 insertions, 0 deletions
diff --git a/modules/woff2/src/variable_length.cc b/modules/woff2/src/variable_length.cc
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+++ b/modules/woff2/src/variable_length.cc
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+// Copyright 2015 Google Inc. All Rights Reserved.
+//
+// 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.
+//
+// Helper functions for woff2 variable length types: 255UInt16 and UIntBase128
+
+#include "./variable_length.h"
+
+namespace woff2 {
+
+size_t Size255UShort(uint16_t value) {
+ size_t result = 3;
+ if (value < 253) {
+ result = 1;
+ } else if (value < 762) {
+ result = 2;
+ } else {
+ result = 3;
+ }
+ return result;
+}
+
+void Write255UShort(std::vector<uint8_t>* out, int value) {
+ if (value < 253) {
+ out->push_back(value);
+ } else if (value < 506) {
+ out->push_back(255);
+ out->push_back(value - 253);
+ } else if (value < 762) {
+ out->push_back(254);
+ out->push_back(value - 506);
+ } else {
+ out->push_back(253);
+ out->push_back(value >> 8);
+ out->push_back(value & 0xff);
+ }
+}
+
+void Store255UShort(int val, size_t* offset, uint8_t* dst) {
+ std::vector<uint8_t> packed;
+ Write255UShort(&packed, val);
+ for (uint8_t val : packed) {
+ dst[(*offset)++] = val;
+ }
+}
+
+// Based on section 6.1.1 of MicroType Express draft spec
+bool Read255UShort(Buffer* buf, unsigned int* value) {
+ static const int kWordCode = 253;
+ static const int kOneMoreByteCode2 = 254;
+ static const int kOneMoreByteCode1 = 255;
+ static const int kLowestUCode = 253;
+ uint8_t code = 0;
+ if (!buf->ReadU8(&code)) {
+ return FONT_COMPRESSION_FAILURE();
+ }
+ if (code == kWordCode) {
+ uint16_t result = 0;
+ if (!buf->ReadU16(&result)) {
+ return FONT_COMPRESSION_FAILURE();
+ }
+ *value = result;
+ return true;
+ } else if (code == kOneMoreByteCode1) {
+ uint8_t result = 0;
+ if (!buf->ReadU8(&result)) {
+ return FONT_COMPRESSION_FAILURE();
+ }
+ *value = result + kLowestUCode;
+ return true;
+ } else if (code == kOneMoreByteCode2) {
+ uint8_t result = 0;
+ if (!buf->ReadU8(&result)) {
+ return FONT_COMPRESSION_FAILURE();
+ }
+ *value = result + kLowestUCode * 2;
+ return true;
+ } else {
+ *value = code;
+ return true;
+ }
+}
+
+bool ReadBase128(Buffer* buf, uint32_t* value) {
+ uint32_t result = 0;
+ for (size_t i = 0; i < 5; ++i) {
+ uint8_t code = 0;
+ if (!buf->ReadU8(&code)) {
+ return FONT_COMPRESSION_FAILURE();
+ }
+ // Leading zeros are invalid.
+ if (i == 0 && code == 0x80) {
+ return FONT_COMPRESSION_FAILURE();
+ }
+ // If any of the top seven bits are set then we're about to overflow.
+ if (result & 0xfe000000) {
+ return FONT_COMPRESSION_FAILURE();
+ }
+ result = (result << 7) | (code & 0x7f);
+ if ((code & 0x80) == 0) {
+ *value = result;
+ return true;
+ }
+ }
+ // Make sure not to exceed the size bound
+ return FONT_COMPRESSION_FAILURE();
+}
+
+size_t Base128Size(size_t n) {
+ size_t size = 1;
+ for (; n >= 128; n >>= 7) ++size;
+ return size;
+}
+
+void StoreBase128(size_t len, size_t* offset, uint8_t* dst) {
+ size_t size = Base128Size(len);
+ for (size_t i = 0; i < size; ++i) {
+ int b = static_cast<int>((len >> (7 * (size - i - 1))) & 0x7f);
+ if (i < size - 1) {
+ b |= 0x80;
+ }
+ dst[(*offset)++] = b;
+ }
+}
+
+} // namespace woff2
+