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// Copyright 2019 The libgav1 Authors
//
// 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.
#include "src/utils/bit_reader.h"
#include <cassert>
#include <cstdint>
#include "src/utils/common.h"
namespace libgav1 {
namespace {
bool Assign(int* const value, int assignment, bool return_value) {
*value = assignment;
return return_value;
}
// 5.9.29.
int InverseRecenter(int r, int v) {
if (v > (r << 1)) {
return v;
}
if ((v & 1) != 0) {
return r - ((v + 1) >> 1);
}
return r + (v >> 1);
}
} // namespace
bool BitReader::DecodeSignedSubexpWithReference(int low, int high,
int reference, int control,
int* const value) {
if (!DecodeUnsignedSubexpWithReference(high - low, reference - low, control,
value)) {
return false;
}
*value += low;
return true;
}
bool BitReader::DecodeUniform(int n, int* const value) {
if (n <= 1) {
return Assign(value, 0, true);
}
const int w = FloorLog2(n) + 1;
const int m = (1 << w) - n;
assert(w - 1 < 32);
const int v = static_cast<int>(ReadLiteral(w - 1));
if (v == -1) {
return Assign(value, 0, false);
}
if (v < m) {
return Assign(value, v, true);
}
const int extra_bit = ReadBit();
if (extra_bit == -1) {
return Assign(value, 0, false);
}
return Assign(value, (v << 1) - m + extra_bit, true);
}
bool BitReader::DecodeUnsignedSubexpWithReference(int mx, int reference,
int control,
int* const value) {
int v;
if (!DecodeSubexp(mx, control, &v)) return false;
if ((reference << 1) <= mx) {
*value = InverseRecenter(reference, v);
} else {
*value = mx - 1 - InverseRecenter(mx - 1 - reference, v);
}
return true;
}
bool BitReader::DecodeSubexp(int num_symbols, int control, int* const value) {
int i = 0;
int mk = 0;
while (true) {
const int b = (i != 0) ? control + i - 1 : control;
if (b >= 32) {
return Assign(value, 0, false);
}
const int a = 1 << b;
if (num_symbols <= mk + 3 * a) {
if (!DecodeUniform(num_symbols - mk, value)) return false;
*value += mk;
return true;
}
const int8_t subexp_more_bits = ReadBit();
if (subexp_more_bits == -1) return false;
if (subexp_more_bits != 0) {
++i;
mk += a;
} else {
const int subexp_bits = static_cast<int>(ReadLiteral(b));
if (subexp_bits == -1) {
return Assign(value, 0, false);
}
return Assign(value, subexp_bits + mk, true);
}
}
}
} // namespace libgav1
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