234 lines
6.4 KiB
C++
234 lines
6.4 KiB
C++
// Copyright (C) 2004 Davis E. King (davis@dlib.net)
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// License: Boost Software License See LICENSE.txt for the full license.
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#ifndef DLIB_ENTROPY_ENCODER_KERNEL_2_CPp_
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#define DLIB_ENTROPY_ENCODER_KERNEL_2_CPp_
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#include "entropy_encoder_kernel_2.h"
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#include <iostream>
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#include <streambuf>
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namespace dlib
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{
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// ----------------------------------------------------------------------------------------
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entropy_encoder_kernel_2::
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entropy_encoder_kernel_2(
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) :
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initial_low(0x00000001),
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initial_high(0xffffffff),
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out(0),
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low(initial_low),
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high(initial_high)
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{
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}
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// ----------------------------------------------------------------------------------------
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entropy_encoder_kernel_2::
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~entropy_encoder_kernel_2 (
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)
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{
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try {
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if (out != 0)
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{
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flush();
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}
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} catch (...) {}
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}
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// ----------------------------------------------------------------------------------------
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void entropy_encoder_kernel_2::
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clear(
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)
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{
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if (out != 0)
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{
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flush();
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}
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out = 0;
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}
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// ----------------------------------------------------------------------------------------
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void entropy_encoder_kernel_2::
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set_stream (
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std::ostream& out_
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)
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{
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if (out != 0)
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{
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// if a stream is currently set then flush the buffers to it before
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// we switch to the new stream
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flush();
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}
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out = &out_;
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streambuf = out_.rdbuf();
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// reset the encoder state
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low = initial_low;
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high = initial_high;
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}
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// ----------------------------------------------------------------------------------------
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bool entropy_encoder_kernel_2::
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stream_is_set (
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) const
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{
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if (out != 0)
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return true;
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else
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return false;
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}
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// ----------------------------------------------------------------------------------------
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std::ostream& entropy_encoder_kernel_2::
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get_stream (
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) const
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{
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return *out;
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}
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// ----------------------------------------------------------------------------------------
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void entropy_encoder_kernel_2::
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encode (
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uint32 low_count,
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uint32 high_count,
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uint32 total
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)
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{
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// note that we must add one because of the convention that
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// high == the real upper range minus 1
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uint32 r = (high-low+1)/total;
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// note that we must subtract 1 to preserve the convention that
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// high == the real upper range - 1
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high = low + r*high_count-1;
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low = low + r*low_count;
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while (true )
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{
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// if high and low don't have the same 8 high order bits
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if ((high&0xFF000000) != (low&0xFF000000))
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{
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// if the distance between high and low is small and there aren't
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// any bits we can roll off then force high and low to have common high
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// order bits.
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if ((high-low < 0x10000))
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{
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if (high-low > 0x1000)
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{
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high>>=1;
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low>>=1;
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high = low = high+low;
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high += 0xFF;
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low -= 0xFF;
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}
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else /**/
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{
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high>>=1;
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low>>=1;
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high = low = high+low;
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}
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}
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else
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{
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// there are no bits to roll off and high and low are not
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// too close so just quit the loop
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break;
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}
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}
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// else if there are 8 bits we can roll off
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else
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{
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// write the 8 high order bits from low into buf
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unsigned char buf = static_cast<unsigned char>(low>>24);
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// roll off the bits we just wrote to buf
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high <<= 8;
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low <<= 8;
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high |= 0xFF; // note that it is ok to add 0xFF to high here because
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// of the convention that high == real upper range - 1.
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// so that means that if we want to shift the upper range
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// left by one then we must shift a one into high also
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// since real upper range == high + 0.999999999...
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// make sure low is never zero
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if (low == 0)
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low = 1;
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// write buf to the output stream
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if (streambuf->sputn(reinterpret_cast<char*>(&buf),1)==0)
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{
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throw std::ios_base::failure("error occured in the entropy_encoder object");
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}
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}
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} // while (true)
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}
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// ----------------------------------------------------------------------------------------
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void entropy_encoder_kernel_2::
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flush (
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)
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{
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// flush low to the output stream
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unsigned char buf;
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buf = static_cast<unsigned char>((low >> 24)&0xFF);
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if (streambuf->sputn(reinterpret_cast<char*>(&buf),1) == 0)
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throw std::ios_base::failure("error occured in the entropy_encoder object");
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buf = static_cast<unsigned char>((low >> 16)&0xFF);
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if (streambuf->sputn(reinterpret_cast<char*>(&buf),1)==0)
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throw std::ios_base::failure("error occured in the entropy_encoder object");
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buf = static_cast<unsigned char>((low >> 8)&0xFF);
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if (streambuf->sputn(reinterpret_cast<char*>(&buf),1)==0)
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throw std::ios_base::failure("error occured in the entropy_encoder object");
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buf = static_cast<unsigned char>((low)&0xFF);
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if (streambuf->sputn(reinterpret_cast<char*>(&buf),1)==0)
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throw std::ios_base::failure("error occured in the entropy_encoder object");
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// make sure the stream buffer flushes to its I/O channel
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streambuf->pubsync();
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// reset the encoder state
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low = initial_low;
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high = initial_high;
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}
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// ----------------------------------------------------------------------------------------
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}
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#endif // DLIB_ENTROPY_ENCODER_KERNEL_2_CPp_
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