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diff --git a/sms/spectralApprox.c b/sms/spectralApprox.c
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+/* 
+ * Copyright (c) 2008 MUSIC TECHNOLOGY GROUP (MTG)
+ *                         UNIVERSITAT POMPEU FABRA 
+ * 
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of 
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ * 
+ */
+/*! \file spectralApprox.c
+ * \brief line segment approximation of a magnitude spectrum
+ */
+#include "sms.h"
+
+/*! \brief approximate a magnitude spectrum
+ * First downsampling using local maxima and then upsampling using linear 
+ * interpolation. The output spectrum doesn't have to be the same size as 
+ * the input one.
+ *
+ * \param pFSpec1     magnitude spectrum to approximate
+ * \param sizeSpec1       size of input spectrum
+ * \param sizeSpec1Used  size of the spectrum to use
+ * \param pFSpec2     output envelope
+ * \param sizeSpec2      size of output envelope
+ * \param nCoefficients  number of coefficients to use in approximation
+ * \return error code \see SMS_ERRORS (or -1 if the algorithm just messes up, 
+               it will print an error of its own.
+ */
+int sms_spectralApprox (sfloat *pFSpec1, int sizeSpec1, int sizeSpec1Used,
+                    sfloat *pFSpec2, int sizeSpec2, int nCoefficients)
+{
+	sfloat fHopSize, fCurrentLoc = 0, fLeft = 0, fRight = 0, fValue = 0, 
+		fLastLocation, fSizeX, fSpec2Acum=0, fNextHop, fDeltaY, *pFEnvelope;
+	int iFirstGood = 0, iLastSample = 0, i, j;
+
+  	/* when number of coefficients is smaller than 2 do not approximate */
+	if (nCoefficients < 2)
+	{
+		for (i = 0; i < sizeSpec2; i++)
+			pFSpec2[i] = 1;
+		return(SMS_OK);
+	}
+
+	if ((pFEnvelope = (sfloat *) calloc(nCoefficients, sizeof(sfloat))) == NULL)
+		return(SMS_MALLOC);
+ 
+	/* calculate the hop size */
+	if (sizeSpec1 != sizeSpec1Used)
+                fHopSize = (sfloat) sizeSpec1Used / nCoefficients;
+	else //why is this here, would be the same as sizeSpec1Used / nCoefficients
+		fHopSize = (sfloat) sizeSpec1 / nCoefficients;
+        if(nCoefficients > sizeSpec1)
+                nCoefficients = sizeSpec1;
+
+        fHopSize = (sfloat) sizeSpec1Used / nCoefficients;
+        
+	/* approximate by linear interpolation */
+	if (fHopSize > 1)
+	{
+		iFirstGood = 0;
+		for (i = 0; i < nCoefficients; i++)
+		{
+			iLastSample = fLastLocation = fCurrentLoc + fHopSize;
+			iLastSample = MIN (sizeSpec1-1, iLastSample);
+			if (iLastSample < sizeSpec1-1)
+				fRight = pFSpec1[iLastSample] +
+					(pFSpec1[iLastSample+1] - pFSpec1[iLastSample]) * 
+					(fLastLocation - iLastSample);
+			else
+				fRight = pFSpec1[iLastSample];
+			fValue = 0;
+			for (j = iFirstGood; j <= iLastSample; j++)
+				fValue = MAX (fValue, pFSpec1[j]);
+			fValue = MAX (fValue, MAX (fRight, fLeft));
+			pFEnvelope[i] = fValue;
+			fLeft = fRight;
+			fCurrentLoc = fLastLocation;
+			iFirstGood = (int) (1+ fCurrentLoc);
+		}
+	}
+	else if (fHopSize == 1)
+	{
+		for (i = 0; i < nCoefficients; i++)
+			pFEnvelope[i] = pFSpec1[i];
+	}
+	else
+	{
+		free (pFEnvelope);
+		//printf ("SpectralApprox: sizeSpec1 has too many nCoefficients\n"); /* \todo need to increase the frequency? */
+		sms_error ("SpectralApprox: sizeSpec1 has too many nCoefficients\n"); /* \todo need to increase the frequency? */
+		return -1;
+	}
+
+	/* Creates Spec2 from Envelope */
+	if (nCoefficients < sizeSpec2)
+	{
+		fSizeX = (sfloat) (sizeSpec2-1) / nCoefficients;
+
+		/* the first step */
+		fNextHop = fSizeX / 2;
+		fDeltaY = pFEnvelope[0] / fNextHop;
+		fSpec2Acum=pFSpec2[j=0]=0;
+		while (++j < fNextHop)  
+			pFSpec2[j] = (fSpec2Acum += fDeltaY);
+     
+		/* middle values */
+		for (i = 0; i <= nCoefficients-2; ++i) 
+		{
+			fDeltaY = (pFEnvelope[i+1] - pFEnvelope[i]) / fSizeX;
+			/* first point of a segment */
+			pFSpec2[j] = (fSpec2Acum = (pFEnvelope[i]+(fDeltaY*(j-fNextHop))));
+			++j;
+			/* remaining points */
+			fNextHop += fSizeX;
+			while (j < fNextHop)  
+				pFSpec2[j++] = (fSpec2Acum += fDeltaY);
+    	}
+
+		/* last step */
+		fDeltaY = -pFEnvelope[i] * 2 / fSizeX;
+		/* first point of the last segment */
+		pFSpec2[j] = (fSpec2Acum = (pFEnvelope[i]+(fDeltaY*(j-fNextHop))));
+		++j;
+		fNextHop += fSizeX / 2;
+		while (j < sizeSpec2-1)  
+			pFSpec2[j++]=(fSpec2Acum += fDeltaY);
+		/* last should be exactly zero */
+		pFSpec2[sizeSpec2-1] = .0;	
+    }
+	else if (nCoefficients == sizeSpec2)
+	{
+		for (i = 0; i < nCoefficients; i++)
+			pFSpec2[i] = pFEnvelope[i];
+	}
+	else
+	{
+		free (pFEnvelope);
+		//printf ("SpectralApprox: sizeSpec2 has too many nCoefficients\n");
+		sms_error ("SpectralApprox: sizeSpec2 has too many nCoefficients\n");
+		return -1;
+	}
+	free (pFEnvelope); /* \todo make this a static array */
+	return (SMS_OK);
+}