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// Copyright 2014 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 "components/packed_ct_ev_whitelist/bit_stream_reader.h"
#include "base/big_endian.h"
#include "base/logging.h"
#include "base/numerics/safe_conversions.h"
namespace packed_ct_ev_whitelist {
namespace internal {
BitStreamReader::BitStreamReader(const base::StringPiece& source)
: source_(source), current_byte_(0), current_bit_(7) {
DCHECK_LT(source_.length(), UINT32_MAX);
}
bool BitStreamReader::ReadUnaryEncoding(uint64_t* out) {
if (BitsLeft() == 0)
return false;
*out = 0;
while ((BitsLeft() > 0) && ReadBit())
++(*out);
return true;
}
bool BitStreamReader::ReadBits(uint8_t num_bits, uint64_t* out) {
DCHECK_LE(num_bits, 64);
if (BitsLeft() < num_bits)
return false;
*out = 0;
for (; num_bits && (current_bit_ != 7); --num_bits)
(*out) |= (static_cast<uint64_t>(ReadBit()) << (num_bits - 1));
for (; num_bits / 8; num_bits -= 8)
(*out) |= (static_cast<uint64_t>(ReadByte()) << (num_bits - 8));
for (; num_bits; --num_bits)
(*out) |= (static_cast<uint64_t>(ReadBit()) << (num_bits - 1));
return true;
}
uint64_t BitStreamReader::BitsLeft() const {
if (current_byte_ == source_.length())
return 0;
DCHECK_GT(source_.length(), current_byte_);
return (source_.length() - (current_byte_ + 1)) * 8 + current_bit_ + 1;
}
uint8_t BitStreamReader::ReadBit() {
DCHECK_GT(BitsLeft(), 0u);
DCHECK(current_bit_ < 8 && current_bit_ >= 0);
uint8_t res =
(source_.data()[current_byte_] & (1 << current_bit_)) >> current_bit_;
current_bit_--;
if (current_bit_ < 0) {
current_byte_++;
current_bit_ = 7;
}
return res;
}
uint8_t BitStreamReader::ReadByte() {
DCHECK_GT(BitsLeft(), 7u);
DCHECK_EQ(current_bit_, 7);
return source_.data()[current_byte_++];
}
} // namespace internal
} // namespace packed_ct_ev_whitelist
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