/************************************************************************
*
*       Ron Cohn's implementation       January 1992
*
*   31 Point Equiripple FIR Low-Pass Filter
*
*	Passband:  ripple = 0.5 dB, cutoff =  800 Hz
*	Stopband:  atten. =  40 dB, cutoff = 1240 Hz
*
* Inputs:
*    LEN    - Length of speech buffers
*    NSAMP  - Number of samples to filter
*    INBUF  - Input speech buffer
* Output:
*    LPBUF  - Low passed speech buffer
*/

#include "lpcdefs.h"

void lpfilt31(float inbuf[], float lpbuf[])
{
   int j;
   static float h0  =	-0.0097201988f;
   static float h1  =	-0.0105179986f;
   static float h2  =	-0.0083479648f;
   static float h3  =	 0.0005860774f;
   static float h4  =	 0.0130892089f;
   static float h5  =	 0.0217052232f;
   static float h6  =	 0.0184161253f;
   static float h7  =	 0.0003397230f;
   static float h8  =	-0.0260797087f;
   static float h9  =	-0.0455563702f;
   static float h10 =	-0.0403068550f;
   static float h11 =	 0.0005029835f;
   static float h12 =	 0.0729262903f;
   static float h13 =	 0.1572008878f;
   static float h14 =	 0.2247288674f;
   static float h15 =	 0.2505359650f;
	

   for(j=312+1-180; j<=312; j++)
   {
      lpbuf[j]	= h0  * (inbuf[j   ] + inbuf[j-30]);
      lpbuf[j] += h1  * (inbuf[j -1] + inbuf[j-29]);
      lpbuf[j] += h2  * (inbuf[j -2] + inbuf[j-28]);
      lpbuf[j] += h3  * (inbuf[j -3] + inbuf[j-27]);
      lpbuf[j] += h4  * (inbuf[j -4] + inbuf[j-26]);
      lpbuf[j] += h5  * (inbuf[j -5] + inbuf[j-25]);
      lpbuf[j] += h6  * (inbuf[j -6] + inbuf[j-24]);
      lpbuf[j] += h7  * (inbuf[j -7] + inbuf[j-23]);
      lpbuf[j] += h8  * (inbuf[j -8] + inbuf[j-22]);
      lpbuf[j] += h9  * (inbuf[j -9] + inbuf[j-21]);
      lpbuf[j] += h10 * (inbuf[j-10] + inbuf[j-20]);
      lpbuf[j] += h11 * (inbuf[j-11] + inbuf[j-19]);
      lpbuf[j] += h12 * (inbuf[j-12] + inbuf[j-18]);
      lpbuf[j] += h13 * (inbuf[j-13] + inbuf[j-17]);
      lpbuf[j] += h14 * (inbuf[j-14] + inbuf[j-16]);
      lpbuf[j] += h15 * (inbuf[j-15]		  );
   }
}