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// Copyright (C) 2005 Davis E. King ([email protected])
// License: Boost Software License See LICENSE.txt for the full license.
#ifndef DLIB_COMPRESS_STREAM_KERNEl_3_
#define DLIB_COMPRESS_STREAM_KERNEl_3_
#include "../algs.h"
#include "compress_stream_kernel_abstract.h"
#include "../assert.h"
namespace dlib
{
template <
typename lzp_buf,
typename crc32,
unsigned long buffer_size
>
class compress_stream_kernel_3
{
/*!
REQUIREMENTS ON lzp_buf
is an implementation of lzp_buffer/lzp_buffer_kernel_abstract.h
REQUIREMENTS ON buffer_size
10 < buffer_size < 32
REQUIREMENTS ON crc32
is an implementation of crc32/crc32_kernel_abstract.h
INITIAL VALUE
this object has no state
CONVENTION
this object has no state
This implementation uses the lzp_buffer and writes out matches
in a byte aligned format.
!*/
public:
class decompression_error : public dlib::error
{
public:
decompression_error(
const char* i
) :
dlib::error(std::string(i))
{}
decompression_error(
const std::string& i
) :
dlib::error(i)
{}
};
compress_stream_kernel_3 (
)
{
COMPILE_TIME_ASSERT(10 < buffer_size && buffer_size < 32);
}
~compress_stream_kernel_3 (
)
{}
void compress (
std::istream& in,
std::ostream& out
) const;
void decompress (
std::istream& in,
std::ostream& out
) const;
private:
inline void write (
unsigned char symbol
) const
{
if (out->sputn(reinterpret_cast<char*>(&symbol),1)==0)
throw std::ios_base::failure("error writing to output stream in compress_stream_kernel_3");
}
inline void decode (
unsigned char& symbol,
unsigned char& flag
) const
{
if (count == 0)
{
if (((size_t)in->sgetn(reinterpret_cast<char*>(buffer),sizeof(buffer)))!=sizeof(buffer))
throw decompression_error("Error detected in compressed data stream.");
count = 8;
}
--count;
symbol = buffer[8-count];
flag = buffer[0] >> 7;
buffer[0] <<= 1;
}
inline void encode (
unsigned char symbol,
unsigned char flag
) const
/*!
requires
- 0 <= flag <= 1
ensures
- writes symbol with the given one bit flag
!*/
{
// add this symbol and flag to the buffer
++count;
buffer[0] <<= 1;
buffer[count] = symbol;
buffer[0] |= flag;
if (count == 8)
{
if (((size_t)out->sputn(reinterpret_cast<char*>(buffer),sizeof(buffer)))!=sizeof(buffer))
throw std::ios_base::failure("error writing to output stream in compress_stream_kernel_3");
count = 0;
buffer[0] = 0;
}
}
void clear (
) const
/*!
ensures
- resets the buffers
!*/
{
count = 0;
}
void flush (
) const
/*!
ensures
- flushes any data in the buffers to out
!*/
{
if (count != 0)
{
buffer[0] <<= (8-count);
if (((size_t)out->sputn(reinterpret_cast<char*>(buffer),sizeof(buffer)))!=sizeof(buffer))
throw std::ios_base::failure("error writing to output stream in compress_stream_kernel_3");
}
}
mutable unsigned int count;
// count tells us how many bytes are buffered in buffer and how many flag
// bit are currently in buffer[0]
mutable unsigned char buffer[9];
// buffer[0] holds the flag bits to be writen.
// the rest of the buffer holds the bytes to be writen.
mutable std::streambuf* in;
mutable std::streambuf* out;
// restricted functions
compress_stream_kernel_3(compress_stream_kernel_3<lzp_buf,crc32,buffer_size>&); // copy constructor
compress_stream_kernel_3<lzp_buf,crc32,buffer_size>& operator=(compress_stream_kernel_3<lzp_buf,crc32,buffer_size>&); // assignment operator
};
// ----------------------------------------------------------------------------------------
// ----------------------------------------------------------------------------------------
// member function definitions
// ----------------------------------------------------------------------------------------
// ----------------------------------------------------------------------------------------
template <
typename lzp_buf,
typename crc32,
unsigned long buffer_size
>
void compress_stream_kernel_3<lzp_buf,crc32,buffer_size>::
compress (
std::istream& in_,
std::ostream& out_
) const
{
in = in_.rdbuf();
out = out_.rdbuf();
clear();
crc32 crc;
lzp_buf buffer(buffer_size);
std::streambuf::int_type temp = in->sbumpc();
unsigned long index;
unsigned char symbol;
unsigned char length;
while (temp != EOF)
{
symbol = static_cast<unsigned char>(temp);
if (buffer.predict_match(index))
{
if (buffer[index] == symbol)
{
// this is a match so we must find out how long it is
length = 1;
buffer.add(symbol);
crc.add(symbol);
temp = in->sbumpc();
while (length < 255)
{
if (temp == EOF)
{
break;
}
else if (static_cast<unsigned long>(length) >= index)
{
break;
}
else if (static_cast<unsigned char>(temp) == buffer[index])
{
++length;
buffer.add(static_cast<unsigned char>(temp));
crc.add(static_cast<unsigned char>(temp));
temp = in->sbumpc();
}
else
{
break;
}
}
encode(length,1);
}
else
{
// this is also not a match
encode(symbol,0);
buffer.add(symbol);
crc.add(symbol);
// get the next symbol
temp = in->sbumpc();
}
}
else
{
// there wasn't a match so just write this symbol
encode(symbol,0);
buffer.add(symbol);
crc.add(symbol);
// get the next symbol
temp = in->sbumpc();
}
}
// use a match of zero length to indicate EOF
encode(0,1);
// now write the checksum
unsigned long checksum = crc.get_checksum();
unsigned char byte1 = static_cast<unsigned char>((checksum>>24)&0xFF);
unsigned char byte2 = static_cast<unsigned char>((checksum>>16)&0xFF);
unsigned char byte3 = static_cast<unsigned char>((checksum>>8)&0xFF);
unsigned char byte4 = static_cast<unsigned char>((checksum)&0xFF);
encode(byte1,0);
encode(byte2,0);
encode(byte3,0);
encode(byte4,0);
flush();
}
// ----------------------------------------------------------------------------------------
template <
typename lzp_buf,
typename crc32,
unsigned long buffer_size
>
void compress_stream_kernel_3<lzp_buf,crc32,buffer_size>::
decompress (
std::istream& in_,
std::ostream& out_
) const
{
in = in_.rdbuf();
out = out_.rdbuf();
clear();
crc32 crc;
lzp_buf buffer(buffer_size);
unsigned long index = 0;
unsigned char symbol;
unsigned char length;
unsigned char flag;
decode(symbol,flag);
while (flag == 0 || symbol != 0)
{
buffer.predict_match(index);
if (flag == 1)
{
length = symbol;
do
{
--length;
symbol = buffer[index];
write(symbol);
buffer.add(symbol);
crc.add(symbol);
} while (length != 0);
}
else
{
// this is just a literal
write(symbol);
buffer.add(symbol);
crc.add(symbol);
}
decode(symbol,flag);
}
// now get the checksum and make sure it matches
unsigned char byte1;
unsigned char byte2;
unsigned char byte3;
unsigned char byte4;
decode(byte1,flag);
if (flag != 0)
throw decompression_error("Error detected in compressed data stream.");
decode(byte2,flag);
if (flag != 0)
throw decompression_error("Error detected in compressed data stream.");
decode(byte3,flag);
if (flag != 0)
throw decompression_error("Error detected in compressed data stream.");
decode(byte4,flag);
if (flag != 0)
throw decompression_error("Error detected in compressed data stream.");
unsigned long checksum = byte1;
checksum <<= 8;
checksum |= byte2;
checksum <<= 8;
checksum |= byte3;
checksum <<= 8;
checksum |= byte4;
if (checksum != crc.get_checksum())
throw decompression_error("Error detected in compressed data stream.");
}
// ----------------------------------------------------------------------------------------
}
#endif // DLIB_COMPRESS_STREAM_KERNEl_3_
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