// Copyright (C) 2005 Davis E. King (davis@dlib.net)
// License: Boost Software License See LICENSE.txt for the full license.
#ifndef DLIB_LZP_BUFFER_KERNEl_1_
#define DLIB_LZP_BUFFER_KERNEl_1_
#include "../algs.h"
#include "lzp_buffer_kernel_abstract.h"
namespace dlib
{
template <
typename sbuf
>
class lzp_buffer_kernel_1
{
/*!
REQUIREMENTS ON sbuf
sbuf is an implementation of sliding_buffer/sliding_buffer_kernel_abstract.h
T == unsigned char
INITIAL VALUE
- buffer.size() == the size as defined by the constructor
- table_size == the number of elements in the table array
- for all i: buffer[i] == 0
- for all i: table[i] == buffer.size()
CONVENTION
- table_size == the number of elements in the table array
- size() == buffer.size()
- operator[](i) == buffer[i]
- if (table[hash()] != buffer.size()) then
- buffer.get_element_index(table[hash()]) == the index we will
predict for the current context
- else
- there is no prediction for the current context
- last_element == buffer.size()-1
This is LZP with just an order-3 model without context confirmation.
!*/
public:
explicit lzp_buffer_kernel_1 (
unsigned long buffer_size
);
virtual ~lzp_buffer_kernel_1 (
);
void clear(
);
inline void add (
unsigned char symbol
);
inline unsigned long predict_match (
unsigned long& index
);
inline size_t size (
) const;
inline unsigned char operator[] (
unsigned long index
) const;
private:
inline unsigned long hash (
) const
/*!
ensures
- returns a hash computed from the current context. This hash
is always in the range for table.
!*/
{
unsigned long temp = buffer[0];
temp <<= 16;
unsigned long temp2 = buffer[1];
temp2 <<= 8;
unsigned long temp3 = buffer[2];
temp = temp|temp2|temp3;
temp = ((temp>>11)^temp)&0xFFFF;
return temp;
}
sbuf buffer;
const unsigned long table_size;
unsigned long* const table;
unsigned long last_element;
// restricted functions
lzp_buffer_kernel_1(const lzp_buffer_kernel_1<sbuf>&); // copy constructor
lzp_buffer_kernel_1<sbuf>& operator=(const lzp_buffer_kernel_1<sbuf>&); // assignment operator
};
// ----------------------------------------------------------------------------------------
// ----------------------------------------------------------------------------------------
// member function definitions
// ----------------------------------------------------------------------------------------
// ----------------------------------------------------------------------------------------
template <
typename sbuf
>
lzp_buffer_kernel_1<sbuf>::
lzp_buffer_kernel_1 (
unsigned long buffer_size
) :
table_size(65536),
table(new unsigned long[table_size])
{
buffer.set_size(buffer_size);
for (unsigned long i = 0; i < buffer.size(); ++i)
buffer[i] = 0;
for (unsigned long i = 0; i < table_size; ++i)
table[i] = buffer.size();
last_element = buffer.size()-1;
}
// ----------------------------------------------------------------------------------------
template <
typename sbuf
>
lzp_buffer_kernel_1<sbuf>::
~lzp_buffer_kernel_1 (
)
{
delete [] table;
}
// ----------------------------------------------------------------------------------------
template <
typename sbuf
>
void lzp_buffer_kernel_1<sbuf>::
clear(
)
{
for (unsigned long i = 0; i < buffer.size(); ++i)
buffer[i] = 0;
for (unsigned long i = 0; i < table_size; ++i)
table[i] = buffer.size();
}
// ----------------------------------------------------------------------------------------
template <
typename sbuf
>
void lzp_buffer_kernel_1<sbuf>::
add (
unsigned char symbol
)
{
buffer.rotate_left(1);
buffer[0] = symbol;
}
// ----------------------------------------------------------------------------------------
template <
typename sbuf
>
unsigned long lzp_buffer_kernel_1<sbuf>::
predict_match (
unsigned long& index
)
{
const unsigned long i = hash();
if (table[i] != buffer.size())
{
index = buffer.get_element_index(table[i]);
if (index > 20)
{
// update the prediction for this context
table[i] = buffer.get_element_id(last_element);
}
return 3;
}
else
{
// update the prediction for this context
table[i] = buffer.get_element_id(last_element);
return 0;
}
}
// ----------------------------------------------------------------------------------------
template <
typename sbuf
>
size_t lzp_buffer_kernel_1<sbuf>::
size (
) const
{
return buffer.size();
}
// ----------------------------------------------------------------------------------------
template <
typename sbuf
>
unsigned char lzp_buffer_kernel_1<sbuf>::
operator[] (
unsigned long index
) const
{
return buffer[index];
}
// ----------------------------------------------------------------------------------------
}
#endif // DLIB_LZP_BUFFER_KERNEl_1_