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    /*
    
    $Log$
    
    Revision 1.16  2004/06/26 03:50:14  markster
    Merge source cleanups (bug #1911)
    
    
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    Revision 1.15  2003/09/19 01:20:22  markster
    Code cleanups (bug #66)
    
    Revision 1.2  2003/09/19 01:20:22  markster
    Code cleanups (bug #66)
    
    
    Revision 1.1.1.1  2003/02/12 13:59:15  matteo
    mer feb 12 14:56:57 CET 2003
    
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    Revision 1.2  2000/01/05 08:20:39  markster
    Some OSS fixes and a few lpc changes to make it actually work
    
     * Revision 1.1  1996/08/19  22:31:53  jaf
     * Initial revision
     *
    
    */
    
    /*  -- translated by f2c (version 19951025).
       You must link the resulting object file with the libraries:
    	-lf2c -lm   (in that order)
    */
    
    #include "f2c.h"
    
    
    #ifdef P_R_O_T_O_T_Y_P_E_S
    extern int ivfilt_(real *lpbuf, real *ivbuf, integer *len, integer *nsamp, real *ivrc);
    #endif
    
    
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    /* ********************************************************************* */
    
    /* 	IVFILT Version 48 */
    
    /* $Log$
    
     * Revision 1.16  2004/06/26 03:50:14  markster
     * Merge source cleanups (bug #1911)
    
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     *
    
     * Revision 1.15  2003/09/19 01:20:22  markster
     * Code cleanups (bug #66)
     *
     * Revision 1.2  2003/09/19 01:20:22  markster
     * Code cleanups (bug #66)
     *
     * Revision 1.1.1.1  2003/02/12 13:59:15  matteo
     * mer feb 12 14:56:57 CET 2003
     *
     * Revision 1.2  2000/01/05 08:20:39  markster
     * Some OSS fixes and a few lpc changes to make it actually work
     *
    
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     * Revision 1.1  1996/08/19  22:31:53  jaf
     * Initial revision
     * */
    /* Revision 1.3  1996/03/15  21:36:29  jaf */
    /* Just added a few comments about which array indices of the arguments */
    /* are used, and mentioning that this subroutine has no local state. */
    
    /* Revision 1.2  1996/03/13  00:01:00  jaf */
    /* Comments added explaining that none of the local variables of this */
    /* subroutine need to be saved from one invocation to the next. */
    
    /* Revision 1.1  1996/02/07 14:47:34  jaf */
    /* Initial revision */
    
    
    /* ********************************************************************* */
    
    /*   2nd order inverse filter, speech is decimated 4:1 */
    
    /* Input: */
    /*  LEN    - Length of speech buffers */
    /*  NSAMP  - Number of samples to filter */
    /*  LPBUF  - Low pass filtered speech buffer */
    /*           Indices LEN-NSAMP-7 through LEN read. */
    /* Output: */
    /*  IVBUF  - Inverse filtered speech buffer */
    /*           Indices LEN-NSAMP+1 through LEN written. */
    /*  IVRC   - Inverse filter reflection coefficients (for voicing) */
    /*          Indices 1 and 2 both written (also read, but only after writing).
    */
    
    /* This subroutine has no local state. */
    
    /* Subroutine */ int ivfilt_(real *lpbuf, real *ivbuf, integer *len, integer *
    	nsamp, real *ivrc)
    {
        /* System generated locals */
        integer i__1;
    
        /* Local variables */
        integer i__, j, k;
        real r__[3], pc1, pc2;
    
    /* 	Arguments */
    /*       Local variables that need not be saved */
    /*       Local state */
    /*       None */
    /*  Calculate Autocorrelations */
        /* Parameter adjustments */
        --ivbuf;
        --lpbuf;
        --ivrc;
    
        /* Function Body */
        for (i__ = 1; i__ <= 3; ++i__) {
    	r__[i__ - 1] = 0.f;
    
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    	k = (i__ - 1) << 2;
    
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    	i__1 = *len;
    	for (j = (i__ << 2) + *len - *nsamp; j <= i__1; j += 2) {
    	    r__[i__ - 1] += lpbuf[j] * lpbuf[j - k];
    	}
        }
    /*  Calculate predictor coefficients */
        pc1 = 0.f;
        pc2 = 0.f;
        ivrc[1] = 0.f;
        ivrc[2] = 0.f;
        if (r__[0] > 1e-10f) {
    	ivrc[1] = r__[1] / r__[0];
    	ivrc[2] = (r__[2] - ivrc[1] * r__[1]) / (r__[0] - ivrc[1] * r__[1]);
    	pc1 = ivrc[1] - ivrc[1] * ivrc[2];
    	pc2 = ivrc[2];
        }
    /*  Inverse filter LPBUF into IVBUF */
        i__1 = *len;
        for (i__ = *len + 1 - *nsamp; i__ <= i__1; ++i__) {
    	ivbuf[i__] = lpbuf[i__] - pc1 * lpbuf[i__ - 4] - pc2 * lpbuf[i__ - 8];
        }
        return 0;
    } /* ivfilt_ */