82 lines
2.4 KiB
C++
82 lines
2.4 KiB
C++
// Copyright 2016 The Draco Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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#ifndef DRACO_CORE_VARINT_DECODING_H_
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#define DRACO_CORE_VARINT_DECODING_H_
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#include <type_traits>
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#include "draco/core/bit_utils.h"
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#include "draco/core/decoder_buffer.h"
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namespace draco {
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namespace {
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// Decodes a specified unsigned integer as varint. |depth| is the current
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// recursion call depth. The first call to the function must be 1.
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template <typename IntTypeT>
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bool DecodeVarintUnsigned(int depth, IntTypeT *out_val, DecoderBuffer *buffer) {
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constexpr IntTypeT max_depth = sizeof(IntTypeT) + 1 + (sizeof(IntTypeT) >> 3);
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if (depth > max_depth) {
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return false;
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}
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// Coding of unsigned values.
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// 0-6 bit - data
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// 7 bit - next byte?
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uint8_t in;
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if (!buffer->Decode(&in)) {
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return false;
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}
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if (in & (1 << 7)) {
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// Next byte is available, decode it first.
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if (!DecodeVarintUnsigned<IntTypeT>(depth + 1, out_val, buffer)) {
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return false;
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}
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// Append decoded info from this byte.
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*out_val <<= 7;
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*out_val |= in & ((1 << 7) - 1);
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} else {
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// Last byte reached
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*out_val = in;
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}
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return true;
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}
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} // namespace
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// Decodes a specified integer as varint. Note that the IntTypeT must be the
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// same as the one used in the corresponding EncodeVarint() call.
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// out_val is undefined if this returns false.
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template <typename IntTypeT>
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bool DecodeVarint(IntTypeT *out_val, DecoderBuffer *buffer) {
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if (std::is_unsigned<IntTypeT>::value) {
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if (!DecodeVarintUnsigned<IntTypeT>(1, out_val, buffer)) {
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return false;
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}
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} else {
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// IntTypeT is a signed value. Decode the symbol and convert to signed.
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typename std::make_unsigned<IntTypeT>::type symbol;
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if (!DecodeVarintUnsigned(1, &symbol, buffer)) {
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return false;
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}
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*out_val = ConvertSymbolToSignedInt(symbol);
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}
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return true;
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}
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} // namespace draco
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#endif // DRACO_CORE_VARINT_DECODING_H_
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