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// Copyright (C) 2004 Davis E. King (davis@dlib.net)
// License: Boost Software License See LICENSE.txt for the full license.
#ifndef DLIB_ENTROPY_DECODER_KERNEl_2_
#define DLIB_ENTROPY_DECODER_KERNEl_2_
#include "../algs.h"
#include "entropy_decoder_kernel_abstract.h"
#include <iosfwd>
#include "../uintn.h"
namespace dlib
{
class entropy_decoder_kernel_2
{
/*!
GENERAL NOTES
this decoder is implemented using "range" coding
INITIAL VALUE
in == 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()
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_2 (
);
virtual ~entropy_decoder_kernel_2 (
);
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_2(entropy_decoder_kernel_2&); // copy constructor
entropy_decoder_kernel_2& operator=(entropy_decoder_kernel_2&); // assignment operator
// data members
const uint32 initial_low;
const uint32 initial_high;
std::istream* in;
uint32 low;
uint32 high;
uint32 target;
uint32 r;
std::streambuf* streambuf;
};
}
#ifdef NO_MAKEFILE
#include "entropy_decoder_kernel_2.cpp"
#endif
#endif // DLIB_ENTROPY_DECODER_KERNEl_2_
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