| // Copyright (C) 2003 Davis E. King ([email protected]) | |
| // License: Boost Software License See LICENSE.txt for the full license. | |
| namespace dlib | |
| { | |
| class entropy_decoder_kernel_1 | |
| { | |
| /*! | |
| GENERAL NOTES | |
| this decoder is implemented using arithmetic coding | |
| INITIAL VALUE | |
| in == 0 | |
| buf_used == 0 | |
| buf == 0 | |
| initial_low == 0x00000001 (slightly more than zero) | |
| initial_high == 0xffffffff (slightly less than one, 0.99999999976717) | |
| target == 0x00000000 (zero) | |
| low == initial_low | |
| high == initial_high | |
| r == 0 | |
| CONVENTION | |
| if (in != 0) | |
| *in == get_stream() | |
| true == stream_is_set() | |
| streambuf == in->rdbuf() | |
| else | |
| false == stream_is_set() | |
| buf == used to hold fractional byte values which are fed to target. | |
| buf_used == the number of low order bits in buf that are currently | |
| in use | |
| low == the low end of the range used for arithmetic encoding. | |
| this number is used as a 32bit fixed point real number. | |
| the point is fixed just before the first bit, so it is | |
| always in the range [0,1) | |
| low is also never allowed to be zero to avoid overflow | |
| in the calculation (high-low+1)/total. | |
| high == the high end of the range - 1 used for arithmetic encoding. | |
| this number is used as a 32bit fixed point real number. | |
| the point is fixed just before the first bit, so when we | |
| interpret high as a real number then it is always in the | |
| range [0,1) | |
| the range for arithmetic encoding is always | |
| [low,high + 0.9999999...) the 0.9999999... is why | |
| high == real upper range - 1 | |
| target == 32 bits of the fraction produced from an arithmetic encoder. | |
| this number is used as a 32bit fixed point real number. | |
| the point is fixed just before the first bit, so it is | |
| always in the range [0,1) | |
| r == the value (high-low+1)/total from the last call to | |
| get_target() or 0 if get_target_called() should be false | |
| get_target_called() == (r != 0) | |
| !*/ | |
| public: | |
| entropy_decoder_kernel_1 ( | |
| ); | |
| virtual ~entropy_decoder_kernel_1 ( | |
| ); | |
| void clear( | |
| ); | |
| void set_stream ( | |
| std::istream& in | |
| ); | |
| bool stream_is_set ( | |
| ) const; | |
| std::istream& get_stream ( | |
| ) const; | |
| void decode ( | |
| uint32 low_count, | |
| uint32 high_count | |
| ); | |
| bool get_target_called ( | |
| ) const; | |
| uint32 get_target ( | |
| uint32 total | |
| ); | |
| private: | |
| // restricted functions | |
| entropy_decoder_kernel_1(entropy_decoder_kernel_1&); // copy constructor | |
| entropy_decoder_kernel_1& operator=(entropy_decoder_kernel_1&); // assignment operator | |
| // data members | |
| const uint32 initial_low; | |
| const uint32 initial_high; | |
| std::istream* in; | |
| uint32 low; | |
| uint32 high; | |
| unsigned char buf; | |
| uint32 buf_used; | |
| uint32 target; | |
| uint32 r; | |
| std::streambuf* streambuf; | |
| }; | |
| } | |