coco
133 lines
4.1 KiB
C++
133 lines
4.1 KiB
C++
// Copyright (C) 2003 Davis E. King (davis@dlib.net)
|
|
// License: Boost Software License See LICENSE.txt for the full license.
|
|
#ifndef DLIB_ENTROPY_DECODER_KERNEl_1_
|
|
#define DLIB_ENTROPY_DECODER_KERNEl_1_
|
|
|
|
#include "../algs.h"
|
|
#include "entropy_decoder_kernel_abstract.h"
|
|
#include <iosfwd>
|
|
#include "../uintn.h"
|
|
|
|
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;
|
|
|
|
};
|
|
|
|
}
|
|
|
|
#ifdef NO_MAKEFILE
|
|
#include "entropy_decoder_kernel_1.cpp"
|
|
#endif
|
|
|
|
#endif // DLIB_ENTROPY_DECODER_KERNEl_1_
|
|
|