cor.c

来自「4.8kcelp语音压缩编码程序」· C语言 代码 · 共 66 行

/**************************************************************************
*
* NAME
*	cor
*
* FUNCTION
*
*	compute auto-correlation coefficients by direct multiplication
*
* SYNOPSIS
*
*	subroutine cor(rar, idim, n, c0, c)
*
*   formal 
*                       data    I/O
*       name            type    type    function
*       -------------------------------------------------------------------
*       rar             float   i       Input data frame
*       idim            int     i       frame size
*       n               int     i       Number of correlation terms, 
*                                        exclusive C0
*       c0              float   o       C(0)
*       c               float   o       Auto correlation terms C(i), i=1,n
*       
***************************************************************************
*       
* DESCRIPTION
*
*       COR computes the autocorrelation coefficients of the data
*       sequence rar according to the following formula:
*
*              idim
*       C(i) = SUM   rar(k) * rar(k-i)   , where i = 0, ..., n lags
*              k=i+1
*
*       c0 = C(0)
*
*	NOTE:  rar(k-i) is truncated, so C(i) are true autocorrelations.
*
***************************************************************************
*
* CALLED BY
*
*	autohf	distortion
*
* CALLS
*
*
*
**************************************************************************/
cor(rar, idim, n, c0, c)
int idim, n;
float *rar, *c0, *c;
{
  int i, k;
  
  for (*c0 = 0.0, i = 0; i < idim; i++)
    *c0 += *(rar+i) * *(rar+i);

  for (i = 0; i < n; i++)
  {
    for (*(c+i) = 0.0, k = i+1; k < idim; k++)
      *(c+i) += *(rar+k) * *(rar+k-i-1);
  }
}