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/*!
*************************************************************************************
* \file biaridecod.c
*
* \brief
* Binary arithmetic decoder routines.
*
* This modified implementation of the M Coder is based on JVT-U084
* with the choice of M_BITS = 16.
*
* \date
* 21. Oct 2000
* \author
* Main contributors (see contributors.h for copyright, address and affiliation details)
* - Detlev Marpe <marpe@hhi.de>
* - Gabi Blaettermann
* - Gunnar Marten
*************************************************************************************
*/
#include "global.h"
#include "memalloc.h"
#include "biaridecod.h"
#define B_BITS 10 // Number of bits to represent the whole coding interval
#define HALF 0x01FE //(1 << (B_BITS-1)) - 2
#define QUARTER 0x0100 //(1 << (B_BITS-2))
/************************************************************************
************************************************************************
init / exit decoder
************************************************************************
************************************************************************/
/*!
************************************************************************
* \brief
* Allocates memory for the DecodingEnvironment struct
* \return DecodingContextPtr
* allocates memory
************************************************************************
*/
DecodingEnvironmentPtr arideco_create_decoding_environment()
{
DecodingEnvironmentPtr dep;
if ((dep = calloc(1,sizeof(DecodingEnvironment))) == NULL)
no_mem_exit("arideco_create_decoding_environment: dep");
return dep;
}
/*!
***********************************************************************
* \brief
* Frees memory of the DecodingEnvironment struct
***********************************************************************
*/
void arideco_delete_decoding_environment(DecodingEnvironmentPtr dep)
{
if (dep == NULL)
{
snprintf(errortext, ET_SIZE, "Error freeing dep (NULL pointer)");
error (errortext, 200);
}
else
free(dep);
}
/*!
************************************************************************
* \brief
* finalize arithetic decoding():
************************************************************************
*/
void arideco_done_decoding(DecodingEnvironmentPtr dep)
{
(*dep->Dcodestrm_len)++;
#if(TRACE==2)
fprintf(p_trace, "done_decoding: %d\n", *dep->Dcodestrm_len);
#endif
}
/*!
************************************************************************
* \brief
* read one byte from the bitstream
************************************************************************
*/
unsigned int getbyte(DecodingEnvironmentPtr dep)
{
#if(TRACE==2)
fprintf(p_trace, "get_byte: %d\n", (*dep->Dcodestrm_len));
#endif
return dep->Dcodestrm[(*dep->Dcodestrm_len)++];
}
/*!
************************************************************************
* \brief
* read two bytes from the bitstream
************************************************************************
*/
static unsigned int getword(DecodingEnvironmentPtr dep)
{
int d = *dep->Dcodestrm_len;
*dep->Dcodestrm_len += 2;
return ((dep->Dcodestrm[d]<<8) | dep->Dcodestrm[d+1]);
}
/*!
************************************************************************
* \brief
* Initializes the DecodingEnvironment for the arithmetic coder
************************************************************************
*/
void arideco_start_decoding(DecodingEnvironmentPtr dep, unsigned char *code_buffer,
int firstbyte, int *code_len)
{
dep->Dcodestrm = code_buffer;
dep->Dcodestrm_len = code_len;
*dep->Dcodestrm_len = firstbyte;
dep->Dvalue = getbyte(dep);
dep->Dvalue = (dep->Dvalue << 16) | getword(dep); // lookahead of 2 bytes: always make sure that bitstream buffer
// contains 2 more bytes than actual bitstream
dep->DbitsLeft = 15;
dep->Drange = HALF;
#if (2==TRACE)
fprintf(p_trace, "value: %d firstbyte: %d code_len: %d\n", dep->Dvalue >> dep->DbitsLeft, firstbyte, *code_len);
#endif
}
/*!
************************************************************************
* \brief
* biari_decode_symbol():
* \return
* the decoded symbol
************************************************************************
*/
/* random notes
max rLPS = 240 1111 1 111
max state = 63
max renorm = 6, min 1
max bitsleft = 16
max range = (1<<10) ????? (1024)
*/
#if !defined(_M_IX86) || defined(_DEBUG)
unsigned int biari_decode_symbol(DecodingEnvironmentPtr dep, BiContextTypePtr bi_ct )
{
unsigned int state = bi_ct->state;
unsigned int bit = bi_ct->MPS;
unsigned int value = dep->Dvalue;
unsigned int range = dep->Drange;
const unsigned int rLPS = rLPS_table_64x4[(range>>6)&3][state];
range -= rLPS;
if(value >= (range << dep->DbitsLeft))
{ // LPS
int renorm;
bi_ct->state = AC_next_state_LPS_64[state]; // next state
value -= (range << dep->DbitsLeft);
bit ^= 0x01;
//if (!state) // switch meaning of MPS if necessary
// bi_ct->MPS = bit;
bi_ct->MPS ^= !state;//0x01;
renorm = renorm_table_256[rLPS];
range = (rLPS << renorm);
dep->Drange = range;
dep->DbitsLeft -= renorm;
if( dep->DbitsLeft > 0 )
{
dep->Dvalue = value;
return(bit);
}
dep->Dvalue = (value << 16) | getword(dep); // lookahead of 2 bytes: always make sure that bitstream buffer
// contains 2 more bytes than actual bitstream
dep->DbitsLeft += 16;
return(bit);
}
else
{ //MPS
bi_ct->state = AC_next_state_MPS_64[state]; // next state
if( range < QUARTER )
{
dep->Drange = range << 1;
dep->DbitsLeft -= 1;
if( dep->DbitsLeft > 0 )
{
return(bit);
}
dep->Dvalue = (value << 16) | getword(dep); // lookahead of 2 bytes: always make sure that bitstream buffer
// contains 2 more bytes than actual bitstream
dep->DbitsLeft += 16;
return(bit);
}
else
{
dep->Drange = range;
return (bit);
}
}
}
#endif
/*!
************************************************************************
* \brief
* biari_decode_symbol_eq_prob():
* \return
* the decoded symbol
************************************************************************
*/
unsigned int biari_decode_symbol_eq_prob(DecodingEnvironmentPtr dep)
{
int tmp_value;
int value = dep->Dvalue;
if(--(dep->DbitsLeft) == 0)
{
value = (value << 16) | getword( dep ); // lookahead of 2 bytes: always make sure that bitstream buffer
// contains 2 more bytes than actual bitstream
dep->DbitsLeft = 16;
}
tmp_value = value - (dep->Drange << dep->DbitsLeft);
if (tmp_value < 0)
{
dep->Dvalue = value;
return 0;
}
else
{
dep->Dvalue = tmp_value;
return 1;
}
}
/*!
************************************************************************
* \brief
* biari_decode_symbol_final():
* \return
* the decoded symbol
************************************************************************
*/
unsigned int biari_decode_final(DecodingEnvironmentPtr dep)
{
unsigned int range = dep->Drange - 2;
int value = dep->Dvalue;
value -= (range << dep->DbitsLeft);
if (value < 0)
{
if( range >= QUARTER )
{
dep->Drange = range;
return 0;
}
else
{
dep->Drange = (range << 1);
if( --(dep->DbitsLeft) > 0 )
return 0;
else
{
dep->Dvalue = (dep->Dvalue << 16) | getword( dep ); // lookahead of 2 bytes: always make sure that bitstream buffer
// contains 2 more bytes than actual bitstream
dep->DbitsLeft = 16;
return 0;
}
}
}
else
{
return 1;
}
}
/*!
************************************************************************
* \brief
* Initializes a given context with some pre-defined probability state
************************************************************************
*/
void biari_init_context (int qp, BiContextTypePtr ctx, const char* ini)
{
int pstate = ((ini[0]* qp )>>4) + ini[1];
if ( pstate >= 64 )
{
pstate = imin(126, pstate);
ctx->state = (uint16) (pstate - 64);
ctx->MPS = 1;
}
else
{
pstate = imax(1, pstate);
ctx->state = (uint16) (63 - pstate);
ctx->MPS = 0;
}
}
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