bits.c

g.729 fixed point algorithm

/* Version 3.3    Last modified: December 26, 1995 */

/*****************************************************************************/
/* bit stream manipulation routines                                          */
/*****************************************************************************/
#include "typedef.h"
#include "ld8k.h"
#include "tab_ld8k.h"

/* prototypes for local functions */
static void  int2bin(Word16 value, Word16 no_of_bits, Word16 *bitstream);
static Word16   bin2int(Word16 no_of_bits, Word16 *bitstream);

/*----------------------------------------------------------------------------
 * prm2bits_ld8k -converts encoder parameter vector into vector of serial bits
 * bits2prm_ld8k - converts serial received bits to  encoder parameter vector
 *
 * The transmitted parameters are:
 *
 *     LPC:     1st codebook           7+1 bit
 *              2nd codebook           5+5 bit
 *
 *     1st subframe:
 *          pitch period                 8 bit
 *          parity check on 1st period   1 bit
 *          codebook index1 (positions) 13 bit
 *          codebook index2 (signs)      4 bit
 *          pitch and codebook gains   4+3 bit
 *
 *     2nd subframe:
 *          pitch period (relative)      5 bit
 *          codebook index1 (positions) 13 bit
 *          codebook index2 (signs)      4 bit
 *          pitch and codebook gains   4+3 bit
 *----------------------------------------------------------------------------
 */
void prm2bits_ld8k(
 Word16   prm[],           /* input : encoded parameters  (PRM_SIZE parameters)  */
  Word16 bits[]           /* output: serial bits (SERIAL_SIZE ) bits[0] = bfi
                                    bits[1] = 80 */
)
{
   Word16 i;
   *bits++ = SYNC_WORD;     /* bit[0], at receiver this bits indicates BFI */
   *bits++ = SIZE_WORD;     /* bit[1], to be compatible with hardware */

   for (i = 0; i < PRM_SIZE; i++)
     {
        int2bin(prm[i], bitsno[i], bits);
        bits += bitsno[i];
     }

   return;
}

/*----------------------------------------------------------------------------
 * int2bin convert integer to binary and write the bits bitstream array
 *----------------------------------------------------------------------------
 */
static void int2bin(
 Word16 value,             /* input : decimal value */
 Word16 no_of_bits,        /* input : number of bits to use */
 Word16 *bitstream       /* output: bitstream  */
)
{
   Word16 *pt_bitstream;
   Word16   i, bit;

   pt_bitstream = bitstream + no_of_bits;

   for (i = 0; i < no_of_bits; i++)
   {
     bit = value & (Word16)0x0001;      /* get lsb */
     if (bit == 0)
         *--pt_bitstream = BIT_0;
     else
         *--pt_bitstream = BIT_1;
     value >>= 1;
   }
}

/*----------------------------------------------------------------------------
 *  bits2prm_ld8k - converts serial received bits to  encoder parameter vector
 *----------------------------------------------------------------------------
 */
void bits2prm_ld8k(
 Word16 bits[],          /* input : serial bits (80)                       */
 Word16   prm[]            /* output: decoded parameters (11 parameters)     */
)
{
   Word16 i;
   for (i = 0; i < PRM_SIZE; i++)
     {
        prm[i] = bin2int(bitsno[i], bits);
        bits  += bitsno[i];
     }

}

/*----------------------------------------------------------------------------
 * bin2int - read specified bits from bit array  and convert to integer value
 *----------------------------------------------------------------------------
 */
static Word16 bin2int(            /* output: decimal value of bit pattern */
 Word16 no_of_bits,        /* input : number of bits to read */
 Word16 *bitstream       /* input : array containing bits */
)
{
   Word16   value, i;
   Word16 bit;

   value = 0;
   for (i = 0; i < no_of_bits; i++)
   {
     value <<= 1;
     bit = *bitstream++;
     if (bit == BIT_1)  value += 1;
   }
   return(value);
}