other-licenses/7zstub/src/7zip/Compress/RangeCoder/RangeCoderBit.h@97036ab72558 (annotated)
other-licenses/7zstub/src/7zip/Compress/RangeCoder/RangeCoderBit.h
Tue, 06 Jan 2015 21:39:09 +0100
- author
- Michael Schloh von Bennewitz <michael@schloh.com>
- date
- Tue, 06 Jan 2015 21:39:09 +0100
- branch
- TOR_BUG_9701
- changeset 8
- 97036ab72558
- permissions
- -rw-r--r--
Conditionally force memory storage according to privacy.thirdparty.isolate;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.
| michael@0 | 1 | // Compress/RangeCoder/RangeCoderBit.h |
| michael@0 | 2 | |
| michael@0 | 3 | #ifndef __COMPRESS_RANGECODER_BIT_H |
| michael@0 | 4 | #define __COMPRESS_RANGECODER_BIT_H |
| michael@0 | 5 | |
| michael@0 | 6 | #include "RangeCoder.h" |
| michael@0 | 7 | |
| michael@0 | 8 | namespace NCompress { |
| michael@0 | 9 | namespace NRangeCoder { |
| michael@0 | 10 | |
| michael@0 | 11 | const int kNumBitModelTotalBits = 11; |
| michael@0 | 12 | const UInt32 kBitModelTotal = (1 << kNumBitModelTotalBits); |
| michael@0 | 13 | |
| michael@0 | 14 | const int kNumMoveReducingBits = 2; |
| michael@0 | 15 | |
| michael@0 | 16 | const int kNumBitPriceShiftBits = 6; |
| michael@0 | 17 | const UInt32 kBitPrice = 1 << kNumBitPriceShiftBits; |
| michael@0 | 18 | |
| michael@0 | 19 | class CPriceTables |
| michael@0 | 20 | { |
| michael@0 | 21 | public: |
| michael@0 | 22 | static UInt32 ProbPrices[kBitModelTotal >> kNumMoveReducingBits]; |
| michael@0 | 23 | static void Init(); |
| michael@0 | 24 | CPriceTables(); |
| michael@0 | 25 | }; |
| michael@0 | 26 | |
| michael@0 | 27 | template <int numMoveBits> |
| michael@0 | 28 | class CBitModel |
| michael@0 | 29 | { |
| michael@0 | 30 | public: |
| michael@0 | 31 | UInt32 Prob; |
| michael@0 | 32 | void UpdateModel(UInt32 symbol) |
| michael@0 | 33 | { |
| michael@0 | 34 | /* |
| michael@0 | 35 | Prob -= (Prob + ((symbol - 1) & ((1 << numMoveBits) - 1))) >> numMoveBits; |
| michael@0 | 36 | Prob += (1 - symbol) << (kNumBitModelTotalBits - numMoveBits); |
| michael@0 | 37 | */ |
| michael@0 | 38 | if (symbol == 0) |
| michael@0 | 39 | Prob += (kBitModelTotal - Prob) >> numMoveBits; |
| michael@0 | 40 | else |
| michael@0 | 41 | Prob -= (Prob) >> numMoveBits; |
| michael@0 | 42 | } |
| michael@0 | 43 | public: |
| michael@0 | 44 | void Init() { Prob = kBitModelTotal / 2; } |
| michael@0 | 45 | }; |
| michael@0 | 46 | |
| michael@0 | 47 | template <int numMoveBits> |
| michael@0 | 48 | class CBitEncoder: public CBitModel<numMoveBits> |
| michael@0 | 49 | { |
| michael@0 | 50 | public: |
| michael@0 | 51 | void Encode(CEncoder *encoder, UInt32 symbol) |
| michael@0 | 52 | { |
| michael@0 | 53 | /* |
| michael@0 | 54 | encoder->EncodeBit(this->Prob, kNumBitModelTotalBits, symbol); |
| michael@0 | 55 | this->UpdateModel(symbol); |
| michael@0 | 56 | */ |
| michael@0 | 57 | UInt32 newBound = (encoder->Range >> kNumBitModelTotalBits) * this->Prob; |
| michael@0 | 58 | if (symbol == 0) |
| michael@0 | 59 | { |
| michael@0 | 60 | encoder->Range = newBound; |
| michael@0 | 61 | this->Prob += (kBitModelTotal - this->Prob) >> numMoveBits; |
| michael@0 | 62 | } |
| michael@0 | 63 | else |
| michael@0 | 64 | { |
| michael@0 | 65 | encoder->Low += newBound; |
| michael@0 | 66 | encoder->Range -= newBound; |
| michael@0 | 67 | this->Prob -= (this->Prob) >> numMoveBits; |
| michael@0 | 68 | } |
| michael@0 | 69 | if (encoder->Range < kTopValue) |
| michael@0 | 70 | { |
| michael@0 | 71 | encoder->Range <<= 8; |
| michael@0 | 72 | encoder->ShiftLow(); |
| michael@0 | 73 | } |
| michael@0 | 74 | } |
| michael@0 | 75 | UInt32 GetPrice(UInt32 symbol) const |
| michael@0 | 76 | { |
| michael@0 | 77 | return CPriceTables::ProbPrices[ |
| michael@0 | 78 | (((this->Prob - symbol) ^ ((-(int)symbol))) & (kBitModelTotal - 1)) >> kNumMoveReducingBits]; |
| michael@0 | 79 | } |
| michael@0 | 80 | UInt32 GetPrice0() const { return CPriceTables::ProbPrices[this->Prob >> kNumMoveReducingBits]; } |
| michael@0 | 81 | UInt32 GetPrice1() const { return CPriceTables::ProbPrices[(kBitModelTotal - this->Prob) >> kNumMoveReducingBits]; } |
| michael@0 | 82 | }; |
| michael@0 | 83 | |
| michael@0 | 84 | |
| michael@0 | 85 | template <int numMoveBits> |
| michael@0 | 86 | class CBitDecoder: public CBitModel<numMoveBits> |
| michael@0 | 87 | { |
| michael@0 | 88 | public: |
| michael@0 | 89 | UInt32 Decode(CDecoder *decoder) |
| michael@0 | 90 | { |
| michael@0 | 91 | UInt32 newBound = (decoder->Range >> kNumBitModelTotalBits) * this->Prob; |
| michael@0 | 92 | if (decoder->Code < newBound) |
| michael@0 | 93 | { |
| michael@0 | 94 | decoder->Range = newBound; |
| michael@0 | 95 | this->Prob += (kBitModelTotal - this->Prob) >> numMoveBits; |
| michael@0 | 96 | if (decoder->Range < kTopValue) |
| michael@0 | 97 | { |
| michael@0 | 98 | decoder->Code = (decoder->Code << 8) | decoder->Stream.ReadByte(); |
| michael@0 | 99 | decoder->Range <<= 8; |
| michael@0 | 100 | } |
| michael@0 | 101 | return 0; |
| michael@0 | 102 | } |
| michael@0 | 103 | else |
| michael@0 | 104 | { |
| michael@0 | 105 | decoder->Range -= newBound; |
| michael@0 | 106 | decoder->Code -= newBound; |
| michael@0 | 107 | this->Prob -= (this->Prob) >> numMoveBits; |
| michael@0 | 108 | if (decoder->Range < kTopValue) |
| michael@0 | 109 | { |
| michael@0 | 110 | decoder->Code = (decoder->Code << 8) | decoder->Stream.ReadByte(); |
| michael@0 | 111 | decoder->Range <<= 8; |
| michael@0 | 112 | } |
| michael@0 | 113 | return 1; |
| michael@0 | 114 | } |
| michael@0 | 115 | } |
| michael@0 | 116 | }; |
| michael@0 | 117 | |
| michael@0 | 118 | }} |
| michael@0 | 119 | |
| michael@0 | 120 | #endif |
