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| 1 // Copyright 2014 The Chromium Authors. All rights reserved. | |
| 2 // Use of this source code is governed by a BSD-style license that can be | |
| 3 // found in the LICENSE file. | |
| 4 | |
| 5 #include "components/packed_ct_ev_whitelist/bit_stream_reader.h" | |
| 6 | |
| 7 #include "base/big_endian.h" | |
| 8 #include "base/logging.h" | |
| 9 #include "base/numerics/safe_conversions.h" | |
| 10 | |
| 11 namespace packed_ct_ev_whitelist { | |
| 12 namespace internal { | |
| 13 | |
| 14 BitStreamReader::BitStreamReader(const base::StringPiece& source) | |
| 15 : source_(source), current_byte_(0), current_bit_(7) { | |
| 16 DCHECK_LT(source_.length(), UINT32_MAX); | |
| 17 } | |
| 18 | |
| 19 bool BitStreamReader::ReadUnaryEncoding(uint64_t* out) { | |
| 20 if (BitsLeft() == 0) | |
| 21 return false; | |
| 22 | |
| 23 *out = 0; | |
| 24 while ((BitsLeft() > 0) && ReadBit()) | |
| 25 ++(*out); | |
| 26 | |
| 27 return true; | |
| 28 } | |
| 29 | |
| 30 bool BitStreamReader::ReadBits(uint8_t num_bits, uint64_t* out) { | |
| 31 DCHECK_LE(num_bits, 64); | |
| 32 | |
| 33 if (BitsLeft() < num_bits) | |
| 34 return false; | |
| 35 | |
| 36 *out = 0; | |
| 37 | |
| 38 for (; num_bits && (current_bit_ != 7); --num_bits) | |
| 39 (*out) |= (static_cast<uint64_t>(ReadBit()) << (num_bits - 1)); | |
| 40 for (; num_bits / 8; num_bits -= 8) | |
| 41 (*out) |= (static_cast<uint64_t>(ReadByte()) << (num_bits - 8)); | |
| 42 for (; num_bits; --num_bits) | |
| 43 (*out) |= (static_cast<uint64_t>(ReadBit()) << (num_bits - 1)); | |
| 44 | |
| 45 return true; | |
| 46 } | |
| 47 | |
| 48 uint64_t BitStreamReader::BitsLeft() const { | |
| 49 if (current_byte_ == source_.length()) | |
| 50 return 0; | |
| 51 DCHECK_GT(source_.length(), current_byte_); | |
| 52 return (source_.length() - (current_byte_ + 1)) * 8 + current_bit_ + 1; | |
| 53 } | |
| 54 | |
| 55 uint8_t BitStreamReader::ReadBit() { | |
| 56 DCHECK_GT(BitsLeft(), 0u); | |
| 57 DCHECK(current_bit_ < 8 && current_bit_ >= 0); | |
| 58 uint8_t res = | |
| 59 (source_.data()[current_byte_] & (1 << current_bit_)) >> current_bit_; | |
| 60 current_bit_--; | |
| 61 if (current_bit_ < 0) { | |
| 62 current_byte_++; | |
| 63 current_bit_ = 7; | |
| 64 } | |
| 65 | |
| 66 return res; | |
| 67 } | |
| 68 | |
| 69 uint8_t BitStreamReader::ReadByte() { | |
| 70 DCHECK_GT(BitsLeft(), 7u); | |
| 71 DCHECK_EQ(current_bit_, 7); | |
| 72 | |
| 73 return source_.data()[current_byte_++]; | |
| 74 | |
| 75 } | |
| 76 | |
| 77 } // namespace internal | |
| 78 } // namespace packed_ct_ev_whitelist | |
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