www.pudn.com > 200411301125332697.rar > p_parity.c

/* 
   ITU-T G.729 Speech Coder ANSI-C Source Code 
   Version 3.3    Last modified: December 26, 1995 
 
   Copyright (c) 1996, 
   AT&T, France Telecom, NTT, Universite de Sherbrooke, Lucent Technologies 
   All rights reserved. 
*/ 
 
/*------------------------------------------------------* 
 * Parity_pitch - compute parity bit for first 6 MSBs   * 
 *------------------------------------------------------*/ 
 
#include "typedef.h" 
#include "basic_op.h" 
#include "ld8k.h" 
 
Word16 Parity_Pitch(    /* output: parity bit (XOR of 6 MSB bits)    */ 
   Word16 pitch_index   /* input : index for which parity to compute */ 
) 
{ 
  Word16 temp, sum, i, bit; 
 
  temp = shr(pitch_index, 1); 
 
  sum = 1; 
  for (i = 0; i <= 5; i++) { 
    temp = shr(temp, 1); 
    bit = temp & (Word16)1; 
    sum = add(sum, bit); 
  } 
  sum = sum & (Word16)1; 
 
 
  return sum; 
} 
 
/*--------------------------------------------------------------------* 
 * check_parity_pitch - check parity of index with transmitted parity * 
 *--------------------------------------------------------------------*/ 
 
Word16  Check_Parity_Pitch( /* output: 0 = no error, 1= error */ 
  Word16 pitch_index,       /* input : index of parameter     */ 
  Word16 parity             /* input : parity bit             */ 
) 
{ 
  Word16 temp, sum, i, bit; 
 
  temp = shr(pitch_index, 1); 
 
  sum = 1; 
  for (i = 0; i <= 5; i++) { 
    temp = shr(temp, 1); 
    bit = temp & (Word16)1; 
    sum = add(sum, bit); 
  } 
  sum = add(sum, parity); 
  sum = sum & (Word16)1; 
 
  return sum; 
}