audioop.c

/***********************************************************
Copyright 1991-1995 by Stichting Mathematisch Centrum, Amsterdam,
The Netherlands.

                        All Rights Reserved

Copyright (c) 2000, BeOpen.com.
Copyright (c) 1995-2000, Corporation for National Research Initiatives.
Copyright (c) 1990-1995, Stichting Mathematisch Centrum.
All rights reserved.

See the file "Misc/COPYRIGHT" for information on usage and
redistribution of this file, and for a DISCLAIMER OF ALL WARRANTIES.

******************************************************************/

/* audioopmodule - Module to detect peak values in arrays */

#include "Python.h"

#if SIZEOF_INT == 4
typedef int Py_Int32;
typedef unsigned int Py_UInt32;
#else
#if SIZEOF_LONG == 4
typedef long Py_Int32;
typedef unsigned long Py_UInt32;
#else
#error "No 4-byte integral type"
#endif
#endif

#if defined(__CHAR_UNSIGNED__)
#if defined(signed)
!ERROR!; READ THE SOURCE FILE!;
/* This module currently does not work on systems where only unsigned
   characters are available.  Take it out of Setup.  Sorry. */
#endif
#endif

#include "mymath.h"

/* Code shamelessly stolen from sox,
** (c) Craig Reese, Joe Campbell and Jeff Poskanzer 1989 */

#define MINLIN -32768
#define MAXLIN 32767
#define LINCLIP(x) do { if ( x < MINLIN ) x = MINLIN ; \
                        else if ( x > MAXLIN ) x = MAXLIN; \
                      } while ( 0 )

static unsigned char st_linear_to_ulaw( /* int sample */ );

/*
** This macro converts from ulaw to 16 bit linear, faster.
**
** Jef Poskanzer
** 23 October 1989
**
** Input: 8 bit ulaw sample
** Output: signed 16 bit linear sample
*/
#define st_ulaw_to_linear(ulawbyte) ulaw_table[ulawbyte]

static int ulaw_table[256] = {
	-32124, -31100, -30076, -29052, -28028, -27004, -25980, -24956,
	-23932, -22908, -21884, -20860, -19836, -18812, -17788, -16764,
	-15996, -15484, -14972, -14460, -13948, -13436, -12924, -12412,
	-11900, -11388, -10876, -10364,  -9852,  -9340,  -8828,  -8316,
	-7932,  -7676,  -7420,  -7164,  -6908,  -6652,  -6396,  -6140,
	-5884,  -5628,  -5372,  -5116,  -4860,  -4604,  -4348,  -4092,
	-3900,  -3772,  -3644,  -3516,  -3388,  -3260,  -3132,  -3004,
	-2876,  -2748,  -2620,  -2492,  -2364,  -2236,  -2108,  -1980,
	-1884,  -1820,  -1756,  -1692,  -1628,  -1564,  -1500,  -1436,
	-1372,  -1308,  -1244,  -1180,  -1116,  -1052,   -988,   -924,
	-876,   -844,   -812,   -780,   -748,   -716,   -684,   -652,
	-620,   -588,   -556,   -524,   -492,   -460,   -428,   -396,
	-372,   -356,   -340,   -324,   -308,   -292,   -276,   -260,
	-244,   -228,   -212,   -196,   -180,   -164,   -148,   -132,
	-120,   -112,   -104,    -96,    -88,    -80,    -72,    -64,
	-56,    -48,    -40,    -32,    -24,    -16,     -8,      0,
	32124,  31100,  30076,  29052,  28028,  27004,  25980,  24956,
	23932,  22908,  21884,  20860,  19836,  18812,  17788,  16764,
	15996,  15484,  14972,  14460,  13948,  13436,  12924,  12412,
	11900,  11388,  10876,  10364,   9852,   9340,   8828,   8316,
	7932,   7676,   7420,   7164,   6908,   6652,   6396,   6140,
	5884,   5628,   5372,   5116,   4860,   4604,   4348,   4092,
	3900,   3772,   3644,   3516,   3388,   3260,   3132,   3004,
	2876,   2748,   2620,   2492,   2364,   2236,   2108,   1980,
	1884,   1820,   1756,   1692,   1628,   1564,   1500,   1436,
	1372,   1308,   1244,   1180,   1116,   1052,    988,    924,
	876,    844,    812,    780,    748,    716,    684,    652,
	620,    588,    556,    524,    492,    460,    428,    396,
	372,    356,    340,    324,    308,    292,    276,    260,
	244,    228,    212,    196,    180,    164,    148,    132,
	120,    112,    104,     96,     88,     80,     72,     64,
	56,     48,     40,     32,     24,     16,      8,      0 };

/* #define ZEROTRAP    /* turn on the trap as per the MIL-STD */
#define BIAS 0x84   /* define the add-in bias for 16 bit samples */
#define CLIP 32635

static unsigned char
st_linear_to_ulaw( sample )
	int sample;
{
	static int exp_lut[256] = {0,0,1,1,2,2,2,2,3,3,3,3,3,3,3,3,
				   4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,
				   5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
				   5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
				   6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
				   6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
				   6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
				   6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
				   7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
				   7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
				   7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
				   7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
				   7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
				   7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
				   7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
				   7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7};
	int sign, exponent, mantissa;
	unsigned char ulawbyte;

	/* Get the sample into sign-magnitude. */
	sign = (sample >> 8) & 0x80;		/* set aside the sign */
	if ( sign != 0 ) sample = -sample;	/* get magnitude */
	if ( sample > CLIP ) sample = CLIP;	/* clip the magnitude */

	/* Convert from 16 bit linear to ulaw. */
	sample = sample + BIAS;
	exponent = exp_lut[( sample >> 7 ) & 0xFF];
	mantissa = ( sample >> ( exponent + 3 ) ) & 0x0F;
	ulawbyte = ~ ( sign | ( exponent << 4 ) | mantissa );
#ifdef ZEROTRAP
	if ( ulawbyte == 0 ) ulawbyte = 0x02;	/* optional CCITT trap */
#endif

	return ulawbyte;
}
/* End of code taken from sox */

/* Intel ADPCM step variation table */
static int indexTable[16] = {
	-1, -1, -1, -1, 2, 4, 6, 8,
	-1, -1, -1, -1, 2, 4, 6, 8,
};

static int stepsizeTable[89] = {
	7, 8, 9, 10, 11, 12, 13, 14, 16, 17,
	19, 21, 23, 25, 28, 31, 34, 37, 41, 45,
	50, 55, 60, 66, 73, 80, 88, 97, 107, 118,
	130, 143, 157, 173, 190, 209, 230, 253, 279, 307,
	337, 371, 408, 449, 494, 544, 598, 658, 724, 796,
	876, 963, 1060, 1166, 1282, 1411, 1552, 1707, 1878, 2066,
	2272, 2499, 2749, 3024, 3327, 3660, 4026, 4428, 4871, 5358,
	5894, 6484, 7132, 7845, 8630, 9493, 10442, 11487, 12635, 13899,
	15289, 16818, 18500, 20350, 22385, 24623, 27086, 29794, 32767
};
    
#define CHARP(cp, i) ((signed char *)(cp+i))
#define SHORTP(cp, i) ((short *)(cp+i))
#define LONGP(cp, i) ((Py_Int32 *)(cp+i))



static PyObject *AudioopError;

static PyObject *
audioop_getsample(self, args)
	PyObject *self;
        PyObject *args;
{
	signed char *cp;
	int len, size, val = 0;
	int i;

	if ( !PyArg_Parse(args, "(s#ii)", &cp, &len, &size, &i) )
		return 0;
	if ( size != 1 && size != 2 && size != 4 ) {
		PyErr_SetString(AudioopError, "Size should be 1, 2 or 4");
		return 0;
	}
	if ( i < 0 || i >= len/size ) {
		PyErr_SetString(AudioopError, "Index out of range");
		return 0;
	}
	if ( size == 1 )      val = (int)*CHARP(cp, i);
	else if ( size == 2 ) val = (int)*SHORTP(cp, i*2);
	else if ( size == 4 ) val = (int)*LONGP(cp, i*4);
	return PyInt_FromLong(val);
}

static PyObject *
audioop_max(self, args)
	PyObject *self;
        PyObject *args;
{
	signed char *cp;
	int len, size, val = 0;
	int i;
	int max = 0;

	if ( !PyArg_Parse(args, "(s#i)", &cp, &len, &size) )
		return 0;
	if ( size != 1 && size != 2 && size != 4 ) {
		PyErr_SetString(AudioopError, "Size should be 1, 2 or 4");
		return 0;
	}
	for ( i=0; i<len; i+= size) {
		if ( size == 1 )      val = (int)*CHARP(cp, i);
		else if ( size == 2 ) val = (int)*SHORTP(cp, i);
		else if ( size == 4 ) val = (int)*LONGP(cp, i);
		if ( val < 0 ) val = (-val);
		if ( val > max ) max = val;
	}
	return PyInt_FromLong(max);
}

static PyObject *
audioop_minmax(self, args)
	PyObject *self;
        PyObject *args;
{
	signed char *cp;
	int len, size, val = 0;
	int i;
	int min = 0x7fffffff, max = -0x7fffffff;

	if (!PyArg_Parse(args, "(s#i)", &cp, &len, &size))
		return NULL;
	if (size != 1 && size != 2 && size != 4) {
		PyErr_SetString(AudioopError, "Size should be 1, 2 or 4");
		return NULL;
	}
	for (i = 0; i < len; i += size) {
		if (size == 1) val = (int) *CHARP(cp, i);
		else if (size == 2) val = (int) *SHORTP(cp, i);
		else if (size == 4) val = (int) *LONGP(cp, i);
		if (val > max) max = val;
		if (val < min) min = val;
	}
	return Py_BuildValue("(ii)", min, max);
}

static PyObject *
audioop_avg(self, args)
	PyObject *self;
        PyObject *args;
{
	signed char *cp;
	int len, size, val = 0;
	int i;
	double avg = 0.0;

	if ( !PyArg_Parse(args, "(s#i)", &cp, &len, &size) )
		return 0;
	if ( size != 1 && size != 2 && size != 4 ) {
		PyErr_SetString(AudioopError, "Size should be 1, 2 or 4");
		return 0;
	}
	for ( i=0; i<len; i+= size) {
		if ( size == 1 )      val = (int)*CHARP(cp, i);
		else if ( size == 2 ) val = (int)*SHORTP(cp, i);
		else if ( size == 4 ) val = (int)*LONGP(cp, i);
		avg += val;
	}
	if ( len == 0 )
		val = 0;
	else
		val = (int)(avg / (double)(len/size));
	return PyInt_FromLong(val);
}

static PyObject *
audioop_rms(self, args)
	PyObject *self;
        PyObject *args;
{
	signed char *cp;
	int len, size, val = 0;
	int i;
	double sum_squares = 0.0;

	if ( !PyArg_Parse(args, "(s#i)", &cp, &len, &size) )
		return 0;
	if ( size != 1 && size != 2 && size != 4 ) {
		PyErr_SetString(AudioopError, "Size should be 1, 2 or 4");
		return 0;
	}
	for ( i=0; i<len; i+= size) {
		if ( size == 1 )      val = (int)*CHARP(cp, i);
		else if ( size == 2 ) val = (int)*SHORTP(cp, i);
		else if ( size == 4 ) val = (int)*LONGP(cp, i);
		sum_squares += (double)val*(double)val;
	}
	if ( len == 0 )
		val = 0;
	else
		val = (int)sqrt(sum_squares / (double)(len/size));
	return PyInt_FromLong(val);
}

static double _sum2(a, b, len)
	short *a;
        short *b;
        int len;
{
	int i;
	double sum = 0.0;

	for( i=0; i<len; i++) {
		sum = sum + (double)a[i]*(double)b[i];
	}
	return sum;
}

/*
** Findfit tries to locate a sample within another sample. Its main use
** is in echo-cancellation (to find the feedback of the output signal in
** the input signal).
** The method used is as follows:
**
** let R be the reference signal (length n) and A the input signal (length N)
** with N > n, and let all sums be over i from 0 to n-1.
**
** Now, for each j in {0..N-n} we compute a factor fj so that -fj*R matches A
** as good as possible, i.e. sum( (A[j+i]+fj*R[i])^2 ) is minimal. This
** equation gives fj = sum( A[j+i]R[i] ) / sum(R[i]^2).
**
** Next, we compute the relative distance between the original signal and
** the modified signal and minimize that over j:
** vj = sum( (A[j+i]-fj*R[i])^2 ) / sum( A[j+i]^2 )  =>
** vj = ( sum(A[j+i]^2)*sum(R[i]^2) - sum(A[j+i]R[i])^2 ) / sum( A[j+i]^2 )
**
** In the code variables correspond as follows:
** cp1		A
** cp2		R
** len1		N
** len2		n
** aj_m1	A[j-1]
** aj_lm1	A[j+n-1]
** sum_ri_2	sum(R[i]^2)
** sum_aij_2	sum(A[i+j]^2)
** sum_aij_ri	sum(A[i+j]R[i])
**
** sum_ri is calculated once, sum_aij_2 is updated each step and sum_aij_ri
** is completely recalculated each step.
*/
static PyObject *
audioop_findfit(self, args)
	PyObject *self;
        PyObject *args;
{
	short *cp1, *cp2;
	int len1, len2;
	int j, best_j;
	double aj_m1, aj_lm1;
	double sum_ri_2, sum_aij_2, sum_aij_ri, result, best_result, factor;

	if ( !PyArg_Parse(args, "(s#s#)", &cp1, &len1, &cp2, &len2) )
		return 0;
	if ( len1 & 1 || len2 & 1 ) {
		PyErr_SetString(AudioopError, "Strings should be even-sized");
		return 0;
	}
	len1 >>= 1;
	len2 >>= 1;
    
	if ( len1 < len2 ) {
		PyErr_SetString(AudioopError, "First sample should be longer");
		return 0;
	}
	sum_ri_2 = _sum2(cp2, cp2, len2);
	sum_aij_2 = _sum2(cp1, cp1, len2);
	sum_aij_ri = _sum2(cp1, cp2, len2);

	result = (sum_ri_2*sum_aij_2 - sum_aij_ri*sum_aij_ri) / sum_aij_2;

	best_result = result;
	best_j = 0;
	j = 0;

	for ( j=1; j<=len1-len2; j++) {
		aj_m1 = (double)cp1[j-1];
		aj_lm1 = (double)cp1[j+len2-1];

		sum_aij_2 = sum_aij_2 + aj_lm1*aj_lm1 - aj_m1*aj_m1;
		sum_aij_ri = _sum2(cp1+j, cp2, len2);

		result = (sum_ri_2*sum_aij_2 - sum_aij_ri*sum_aij_ri)
			/ sum_aij_2;

		if ( result < best_result ) {
			best_result = result;
			best_j = j;
		}
	
	}

	factor = _sum2(cp1+best_j, cp2, len2) / sum_ri_2;
    
	return Py_BuildValue("(if)", best_j, factor);
}

/*
** findfactor finds a factor f so that the energy in A-fB is minimal.
** See the comment for findfit for details.
*/
static PyObject *
audioop_findfactor(self, args)
	PyObject *self;
        PyObject *args;
{
	short *cp1, *cp2;
	int len1, len2;
	double sum_ri_2, sum_aij_ri, result;

	if ( !PyArg_Parse(args, "(s#s#)", &cp1, &len1, &cp2, &len2) )
		return 0;
	if ( len1 & 1 || len2 & 1 ) {
		PyErr_SetString(AudioopError, "Strings should be even-sized");
		return 0;
	}
	if ( len1 != len2 ) {
		PyErr_SetString(AudioopError, "Samples should be same size");
		return 0;
	}
	len2 >>= 1;
	sum_ri_2 = _sum2(cp2, cp2, len2);
	sum_aij_ri = _sum2(cp1, cp2, len2);

	result = sum_aij_ri / sum_ri_2;

	return PyFloat_FromDouble(result);
}

/*
** findmax returns the index of the n-sized segment of the input sample
** that contains the most energy.
*/
static PyObject *
audioop_findmax(self, args)
	PyObject *self;
        PyObject *args;
{
	short *cp1;
	int len1, len2;
	int j, best_j;
	double aj_m1, aj_lm1;
	double result, best_result;

	if ( !PyArg_Parse(args, "(s#i)", &cp1, &len1, &len2) )
		return 0;
	if ( len1 & 1 ) {
		PyErr_SetString(AudioopError, "Strings should be even-sized");
		return 0;
	}
	len1 >>= 1;
    
	if ( len1 < len2 ) {
		PyErr_SetString(AudioopError, "Input sample should be longer");
		return 0;
	}

	result = _sum2(cp1, cp1, len2);

	best_result = result;
	best_j = 0;
	j = 0;

	for ( j=1; j<=len1-len2; j++) {
		aj_m1 = (double)cp1[j-1];
		aj_lm1 = (double)cp1[j+len2-1];

		result = result + aj_lm1*aj_lm1 - aj_m1*aj_m1;

		if ( result > best_result ) {
			best_result = result;
			best_j = j;
		}
	
	}

	return PyInt_FromLong(best_j);
}

static PyObject *
audioop_avgpp(self, args)
	PyObject *self;
        PyObject *args;
{
	signed char *cp;
	int len, size, val = 0, prevval = 0, prevextremevalid = 0,
		prevextreme = 0;
	int i;
	double avg = 0.0;
	int diff, prevdiff, extremediff, nextreme = 0;

	if ( !PyArg_Parse(args, "(s#i)", &cp, &len, &size) )
		return 0;
	if ( size != 1 && size != 2 && size != 4 ) {
		PyErr_SetString(AudioopError, "Size should be 1, 2 or 4");
		return 0;
	}
	/* Compute first delta value ahead. Also automatically makes us
	** skip the first extreme value
	*/
	if ( size == 1 )      prevval = (int)*CHARP(cp, 0);
	else if ( size == 2 ) prevval = (int)*SHORTP(cp, 0);
	else if ( size == 4 ) prevval = (int)*LONGP(cp, 0);
	if ( size == 1 )      val = (int)*CHARP(cp, size);
	else if ( size == 2 ) val = (int)*SHORTP(cp, size);
	else if ( size == 4 ) val = (int)*LONGP(cp, size);
	prevdiff = val - prevval;
    
	for ( i=size; i<len; i+= size) {
		if ( size == 1 )      val = (int)*CHARP(cp, i);
		else if ( size == 2 ) val = (int)*SHORTP(cp, i);
		else if ( size == 4 ) val = (int)*LONGP(cp, i);
		diff = val - prevval;
		if ( diff*prevdiff < 0 ) {
			/* Derivative changed sign. Compute difference to last
			** extreme value and remember.
			*/
			if ( prevextremevalid ) {
				extremediff = prevval - prevextreme;
				if ( extremediff < 0 )
					extremediff = -extremediff;
				avg += extremediff;
				nextreme++;
			}
			prevextremevalid = 1;
			prevextreme = prevval;
		}
		prevval = val;
		if ( diff != 0 )
			prevdiff = diff;	
	}
	if ( nextreme == 0 )
		val = 0;
	else
		val = (int)(avg / (double)nextreme);
	return PyInt_FromLong(val);
}

static PyObject *
audioop_maxpp(self, args)
	PyObject *self;
        PyObject *args;
{
	signed char *cp;
	int len, size, val = 0, prevval = 0, prevextremevalid = 0,
		prevextreme = 0;
	int i;
	int max = 0;
	int diff, prevdiff, extremediff;

	if ( !PyArg_Parse(args, "(s#i)", &cp, &len, &size) )
		return 0;
	if ( size != 1 && size != 2 && size != 4 ) {
		PyErr_SetString(AudioopError, "Size should be 1, 2 or 4");
		return 0;
	}
	/* Compute first delta value ahead. Also automatically makes us
	** skip the first extreme value
	*/
	if ( size == 1 )      prevval = (int)*CHARP(cp, 0);
	else if ( size == 2 ) prevval = (int)*SHORTP(cp, 0);
	else if ( size == 4 ) prevval = (int)*LONGP(cp, 0);
	if ( size == 1 )      val = (int)*CHARP(cp, size);
	else if ( size == 2 ) val = (int)*SHORTP(cp, size);
	else if ( size == 4 ) val = (int)*LONGP(cp, size);
	prevdiff = val - prevval;

	for ( i=size; i<len; i+= size) {
		if ( size == 1 )      val = (int)*CHARP(cp, i);
		else if ( size == 2 ) val = (int)*SHORTP(cp, i);
		else if ( size == 4 ) val = (int)*LONGP(cp, i);
		diff = val - prevval;
		if ( diff*prevdiff < 0 ) {
			/* Derivative changed sign. Compute difference to
			** last extreme value and remember.
			*/
			if ( prevextremevalid ) {
				extremediff = prevval - prevextreme;
				if ( extremediff < 0 )
					extremediff = -extremediff;
				if ( extremediff > max )
					max = extremediff;
			}
			prevextremevalid = 1;
			prevextreme = prevval;
		}
		prevval = val;
		if ( diff != 0 )
			prevdiff = diff;
	}
	return PyInt_FromLong(max);
}

static PyObject *
audioop_cross(self, args)
	PyObject *self;
        PyObject *args;
{
	signed char *cp;
	int len, size, val = 0;
	int i;
	int prevval, ncross;

	if ( !PyArg_Parse(args, "(s#i)", &cp, &len, &size) )
		return 0;
	if ( size != 1 && size != 2 && size != 4 ) {
		PyErr_SetString(AudioopError, "Size should be 1, 2 or 4");
		return 0;
	}
	ncross = -1;
	prevval = 17; /* Anything <> 0,1 */
	for ( i=0; i<len; i+= size) {
		if ( size == 1 )      val = ((int)*CHARP(cp, i)) >> 7;
		else if ( size == 2 ) val = ((int)*SHORTP(cp, i)) >> 15;
		else if ( size == 4 ) val = ((int)*LONGP(cp, i)) >> 31;
		val = val & 1;
		if ( val != prevval ) ncross++;
		prevval = val;
	}
	return PyInt_FromLong(ncross);
}

static PyObject *
audioop_mul(self, args)
	PyObject *self;
        PyObject *args;
{
	signed char *cp, *ncp;
	int len, size, val = 0;
	double factor, fval, maxval;
	PyObject *rv;
	int i;

	if ( !PyArg_Parse(args, "(s#id)", &cp, &len, &size, &factor ) )
		return 0;
    
	if ( size == 1 ) maxval = (double) 0x7f;
	else if ( size == 2 ) maxval = (double) 0x7fff;
	else if ( size == 4 ) maxval = (double) 0x7fffffff;
	else {
		PyErr_SetString(AudioopError, "Size should be 1, 2 or 4");
		return 0;
	}
    
	rv = PyString_FromStringAndSize(NULL, len);
	if ( rv == 0 )
		return 0;
	ncp = (signed char *)PyString_AsString(rv);
    
    
	for ( i=0; i < len; i += size ) {
		if ( size == 1 )      val = (int)*CHARP(cp, i);
		else if ( size == 2 ) val = (int)*SHORTP(cp, i);
		else if ( size == 4 ) val = (int)*LONGP(cp, i);
		fval = (double)val*factor;
		if ( fval > maxval ) fval = maxval;
		else if ( fval < -maxval ) fval = -maxval;
		val = (int)fval;
		if ( size == 1 )      *CHARP(ncp, i) = (signed char)val;
		else if ( size == 2 ) *SHORTP(ncp, i) = (short)val;
		else if ( size == 4 ) *LONGP(ncp, i) = (Py_Int32)val;
	}
	return rv;
}

static PyObject *
audioop_tomono(self, args)
	PyObject *self;
        PyObject *args;
{
	signed char *cp, *ncp;
	int len, size, val1 = 0, val2 = 0;
	double fac1, fac2, fval, maxval;
	PyObject *rv;
	int i;

	if ( !PyArg_Parse(args, "(s#idd)", &cp, &len, &size, &fac1, &fac2 ) )
		return 0;
    
	if ( size == 1 ) maxval = (double) 0x7f;
	else if ( size == 2 ) maxval = (double) 0x7fff;
	else if ( size == 4 ) maxval = (double) 0x7fffffff;
	else {
		PyErr_SetString(AudioopError, "Size should be 1, 2 or 4");
		return 0;
	}
    
	rv = PyString_FromStringAndSize(NULL, len/2);
	if ( rv == 0 )
		return 0;
	ncp = (signed char *)PyString_AsString(rv);
    
    
	for ( i=0; i < len; i += size*2 ) {
		if ( size == 1 )      val1 = (int)*CHARP(cp, i);
		else if ( size == 2 ) val1 = (int)*SHORTP(cp, i);
		else if ( size == 4 ) val1 = (int)*LONGP(cp, i);
		if ( size == 1 )      val2 = (int)*CHARP(cp, i+1);
		else if ( size == 2 ) val2 = (int)*SHORTP(cp, i+2);
		else if ( size == 4 ) val2 = (int)*LONGP(cp, i+4);
		fval = (double)val1*fac1 + (double)val2*fac2;
		if ( fval > maxval ) fval = maxval;
		else if ( fval < -maxval ) fval = -maxval;
		val1 = (int)fval;
		if ( size == 1 )      *CHARP(ncp, i/2) = (signed char)val1;
		else if ( size == 2 ) *SHORTP(ncp, i/2) = (short)val1;
		else if ( size == 4 ) *LONGP(ncp, i/2)= (Py_Int32)val1;
	}
	return rv;
}

static PyObject *
audioop_tostereo(self, args)
	PyObject *self;
        PyObject *args;
{
	signed char *cp, *ncp;
	int len, size, val1, val2, val = 0;
	double fac1, fac2, fval, maxval;
	PyObject *rv;
	int i;

	if ( !PyArg_Parse(args, "(s#idd)", &cp, &len, &size, &fac1, &fac2 ) )
		return 0;
    
	if ( size == 1 ) maxval = (double) 0x7f;
	else if ( size == 2 ) maxval = (double) 0x7fff;
	else if ( size == 4 ) maxval = (double) 0x7fffffff;
	else {
		PyErr_SetString(AudioopError, "Size should be 1, 2 or 4");
		return 0;
	}
    
	rv = PyString_FromStringAndSize(NULL, len*2);
	if ( rv == 0 )
		return 0;
	ncp = (signed char *)PyString_AsString(rv);
    
    
	for ( i=0; i < len; i += size ) {
		if ( size == 1 )      val = (int)*CHARP(cp, i);
		else if ( size == 2 ) val = (int)*SHORTP(cp, i);
		else if ( size == 4 ) val = (int)*LONGP(cp, i);

		fval = (double)val*fac1;
		if ( fval > maxval ) fval = maxval;
		else if ( fval < -maxval ) fval = -maxval;
		val1 = (int)fval;

		fval = (double)val*fac2;
		if ( fval > maxval ) fval = maxval;
		else if ( fval < -maxval ) fval = -maxval;
		val2 = (int)fval;

		if ( size == 1 )      *CHARP(ncp, i*2) = (signed char)val1;
		else if ( size == 2 ) *SHORTP(ncp, i*2) = (short)val1;
		else if ( size == 4 ) *LONGP(ncp, i*2) = (Py_Int32)val1;

		if ( size == 1 )      *CHARP(ncp, i*2+1) = (signed char)val2;
		else if ( size == 2 ) *SHORTP(ncp, i*2+2) = (short)val2;
		else if ( size == 4 ) *LONGP(ncp, i*2+4) = (Py_Int32)val2;
	}
	return rv;
}

static PyObject *
audioop_add(self, args)
	PyObject *self;
        PyObject *args;
{
	signed char *cp1, *cp2, *ncp;
	int len1, len2, size, val1 = 0, val2 = 0, maxval, newval;
	PyObject *rv;
	int i;

	if ( !PyArg_Parse(args, "(s#s#i)",
			  &cp1, &len1, &cp2, &len2, &size ) )
		return 0;

	if ( len1 != len2 ) {
		PyErr_SetString(AudioopError, "Lengths should be the same");
		return 0;
	}
    
	if ( size == 1 ) maxval = 0x7f;
	else if ( size == 2 ) maxval = 0x7fff;
	else if ( size == 4 ) maxval = 0x7fffffff;
	else {
		PyErr_SetString(AudioopError, "Size should be 1, 2 or 4");
		return 0;
	}

	rv = PyString_FromStringAndSize(NULL, len1);
	if ( rv == 0 )
		return 0;
	ncp = (signed char *)PyString_AsString(rv);

	for ( i=0; i < len1; i += size ) {
		if ( size == 1 )      val1 = (int)*CHARP(cp1, i);
		else if ( size == 2 ) val1 = (int)*SHORTP(cp1, i);
		else if ( size == 4 ) val1 = (int)*LONGP(cp1, i);
	
		if ( size == 1 )      val2 = (int)*CHARP(cp2, i);
		else if ( size == 2 ) val2 = (int)*SHORTP(cp2, i);
		else if ( size == 4 ) val2 = (int)*LONGP(cp2, i);

		newval = val1 + val2;
		/* truncate in case of overflow */
		if (newval > maxval) newval = maxval;
		else if (newval < -maxval) newval = -maxval;
		else if (size == 4 && (newval^val1) < 0 && (newval^val2) < 0)
			newval = val1 > 0 ? maxval : - maxval;

		if ( size == 1 )      *CHARP(ncp, i) = (signed char)newval;
		else if ( size == 2 ) *SHORTP(ncp, i) = (short)newval;
		else if ( size == 4 ) *LONGP(ncp, i) = (Py_Int32)newval;
	}
	return rv;
}

static PyObject *
audioop_bias(self, args)
	PyObject *self;
        PyObject *args;
{
	signed char *cp, *ncp;
	int len, size, val = 0;
	PyObject *rv;
	int i;
	int bias;

	if ( !PyArg_Parse(args, "(s#ii)",
			  &cp, &len, &size , &bias) )
		return 0;

	if ( size != 1 && size != 2 && size != 4) {
		PyErr_SetString(AudioopError, "Size should be 1, 2 or 4");
		return 0;
	}
    
	rv = PyString_FromStringAndSize(NULL, len);
	if ( rv == 0 )
		return 0;
	ncp = (signed char *)PyString_AsString(rv);
    
    
	for ( i=0; i < len; i += size ) {
		if ( size == 1 )      val = (int)*CHARP(cp, i);
		else if ( size == 2 ) val = (int)*SHORTP(cp, i);
		else if ( size == 4 ) val = (int)*LONGP(cp, i);
	
		if ( size == 1 )      *CHARP(ncp, i) = (signed char)(val+bias);
		else if ( size == 2 ) *SHORTP(ncp, i) = (short)(val+bias);
		else if ( size == 4 ) *LONGP(ncp, i) = (Py_Int32)(val+bias);
	}
	return rv;
}

static PyObject *
audioop_reverse(self, args)
	PyObject *self;
        PyObject *args;
{
	signed char *cp;
	unsigned char *ncp;
	int len, size, val = 0;
	PyObject *rv;
	int i, j;

	if ( !PyArg_Parse(args, "(s#i)",
			  &cp, &len, &size) )
		return 0;

	if ( size != 1 && size != 2 && size != 4 ) {
		PyErr_SetString(AudioopError, "Size should be 1, 2 or 4");
		return 0;
	}
    
	rv = PyString_FromStringAndSize(NULL, len);
	if ( rv == 0 )
		return 0;
	ncp = (unsigned char *)PyString_AsString(rv);
    
	for ( i=0; i < len; i += size ) {
		if ( size == 1 )      val = ((int)*CHARP(cp, i)) << 8;
		else if ( size == 2 ) val = (int)*SHORTP(cp, i);
		else if ( size == 4 ) val = ((int)*LONGP(cp, i)) >> 16;

		j = len - i - size;
	
		if ( size == 1 )      *CHARP(ncp, j) = (signed char)(val >> 8);
		else if ( size == 2 ) *SHORTP(ncp, j) = (short)(val);
		else if ( size == 4 ) *LONGP(ncp, j) = (Py_Int32)(val<<16);
	}
	return rv;
}

static PyObject *
audioop_lin2lin(self, args)
	PyObject *self;
        PyObject *args;
{
	signed char *cp;
	unsigned char *ncp;
	int len, size, size2, val = 0;
	PyObject *rv;
	int i, j;

	if ( !PyArg_Parse(args, "(s#ii)",
			  &cp, &len, &size, &size2) )
		return 0;

	if ( (size != 1 && size != 2 && size != 4) ||
	     (size2 != 1 && size2 != 2 && size2 != 4)) {
		PyErr_SetString(AudioopError, "Size should be 1, 2 or 4");
		return 0;
	}
    
	rv = PyString_FromStringAndSize(NULL, (len/size)*size2);
	if ( rv == 0 )
		return 0;
	ncp = (unsigned char *)PyString_AsString(rv);
    
	for ( i=0, j=0; i < len; i += size, j += size2 ) {
		if ( size == 1 )      val = ((int)*CHARP(cp, i)) << 8;
		else if ( size == 2 ) val = (int)*SHORTP(cp, i);
		else if ( size == 4 ) val = ((int)*LONGP(cp, i)) >> 16;

		if ( size2 == 1 )  *CHARP(ncp, j) = (signed char)(val >> 8);
		else if ( size2 == 2 ) *SHORTP(ncp, j) = (short)(val);
		else if ( size2 == 4 ) *LONGP(ncp, j) = (Py_Int32)(val<<16);
	}
	return rv;
}

static int
gcd(a, b)
	int a, b;
{
	while (b > 0) {
		int tmp = a % b;
		a = b;
		b = tmp;
	}
	return a;
}

static PyObject *
audioop_ratecv(self, args)
	PyObject *self;
	PyObject *args;
{
	char *cp, *ncp;
	int len, size, nchannels, inrate, outrate, weightA, weightB;
	int chan, d, *prev_i, *cur_i, cur_o;
	PyObject *state, *samps, *str, *rv = NULL;

	weightA = 1;
	weightB = 0;
	if (!PyArg_ParseTuple(args, "s#iiiiO|ii:ratecv", &cp, &len, &size, &nchannels,
			      &inrate, &outrate, &state, &weightA, &weightB))
		return NULL;
	if (size != 1 && size != 2 && size != 4) {
		PyErr_SetString(AudioopError, "Size should be 1, 2 or 4");
		return NULL;
	}
	if (nchannels < 1) {
		PyErr_SetString(AudioopError, "# of channels should be >= 1");
		return NULL;
	}
	if (weightA < 1 || weightB < 0) {
		PyErr_SetString(AudioopError,
			"weightA should be >= 1, weightB should be >= 0");
		return NULL;
	}
	if (len % (size * nchannels) != 0) {
		PyErr_SetString(AudioopError, "not a whole number of frames");
		return NULL;
	}
	if (inrate <= 0 || outrate <= 0) {
		PyErr_SetString(AudioopError, "sampling rate not > 0");
		return NULL;
	}
	/* divide inrate and outrate by their greatest common divisor */
	d = gcd(inrate, outrate);
	inrate /= d;
	outrate /= d;

	prev_i = (int *) malloc(nchannels * sizeof(int));
	cur_i = (int *) malloc(nchannels * sizeof(int));
	len /= size * nchannels;	/* # of frames */
	if (prev_i == NULL || cur_i == NULL) {
		(void) PyErr_NoMemory();
		goto exit;
	}

	if (state == Py_None) {
		d = -outrate;
		for (chan = 0; chan < nchannels; chan++)
			prev_i[chan] = cur_i[chan] = 0;
	} else {
		if (!PyArg_ParseTuple(state,
				"iO!;audioop.ratecv: illegal state argument",
				&d, &PyTuple_Type, &samps))
			goto exit;
		if (PyTuple_Size(samps) != nchannels) {
			PyErr_SetString(AudioopError,
					"illegal state argument");
			goto exit;
		}
		for (chan = 0; chan < nchannels; chan++) {
			if (!PyArg_ParseTuple(PyTuple_GetItem(samps, chan),
					      "ii:ratecv",&prev_i[chan],&cur_i[chan]))
				goto exit;
		}
	}
	str = PyString_FromStringAndSize(
	      NULL, size * nchannels * (len * outrate + inrate - 1) / inrate);
	if (str == NULL)
		goto exit;
	ncp = PyString_AsString(str);

	for (;;) {
		while (d < 0) {
			if (len == 0) {
				samps = PyTuple_New(nchannels);
				for (chan = 0; chan < nchannels; chan++)
					PyTuple_SetItem(samps, chan,
						Py_BuildValue("(ii)",
							      prev_i[chan],
							      cur_i[chan]));
				if (PyErr_Occurred())
					goto exit;
				len = ncp - PyString_AsString(str);
				if (len == 0) {
					/*don't want to resize to zero length*/
					rv = PyString_FromStringAndSize("", 0);
					Py_DECREF(str);
					str = rv;
				} else if (_PyString_Resize(&str, len) < 0)
					goto exit;
				rv = Py_BuildValue("(O(iO))", str, d, samps);
				Py_DECREF(samps);
				Py_DECREF(str);
				goto exit; /* return rv */
			}
			for (chan = 0; chan < nchannels; chan++) {
				prev_i[chan] = cur_i[chan];
				if (size == 1)
				    cur_i[chan] = ((int)*CHARP(cp, 0)) << 8;
				else if (size == 2)
				    cur_i[chan] = (int)*SHORTP(cp, 0);
				else if (size == 4)
				    cur_i[chan] = ((int)*LONGP(cp, 0)) >> 16;
				cp += size;
				/* implements a simple digital filter */
				cur_i[chan] =
					(weightA * cur_i[chan] +
					 weightB * prev_i[chan]) /
					(weightA + weightB);
			}
			len--;
			d += outrate;
		}
		while (d >= 0) {
			for (chan = 0; chan < nchannels; chan++) {
				cur_o = (prev_i[chan] * d +
					 cur_i[chan] * (outrate - d)) /
					outrate;
				if (size == 1)
				    *CHARP(ncp, 0) = (signed char)(cur_o >> 8);
				else if (size == 2)
				    *SHORTP(ncp, 0) = (short)(cur_o);
				else if (size == 4)
				    *LONGP(ncp, 0) = (Py_Int32)(cur_o<<16);
				ncp += size;
			}
			d -= inrate;
		}
	}
  exit:
	if (prev_i != NULL)
		free(prev_i);
	if (cur_i != NULL)
		free(cur_i);
	return rv;
}

static PyObject *
audioop_lin2ulaw(self, args)
	PyObject *self;
        PyObject *args;
{
	signed char *cp;
	unsigned char *ncp;
	int len, size, val = 0;
	PyObject *rv;
	int i;

	if ( !PyArg_Parse(args, "(s#i)",
			  &cp, &len, &size) )
		return 0;

	if ( size != 1 && size != 2 && size != 4) {
		PyErr_SetString(AudioopError, "Size should be 1, 2 or 4");
		return 0;
	}
    
	rv = PyString_FromStringAndSize(NULL, len/size);
	if ( rv == 0 )
		return 0;
	ncp = (unsigned char *)PyString_AsString(rv);
    
	for ( i=0; i < len; i += size ) {
		if ( size == 1 )      val = ((int)*CHARP(cp, i)) << 8;
		else if ( size == 2 ) val = (int)*SHORTP(cp, i);
		else if ( size == 4 ) val = ((int)*LONGP(cp, i)) >> 16;

		*ncp++ = st_linear_to_ulaw(val);
	}
	return rv;
}

static PyObject *
audioop_ulaw2lin(self, args)
	PyObject *self;
        PyObject *args;
{
	unsigned char *cp;
	unsigned char cval;
	signed char *ncp;
	int len, size, val;
	PyObject *rv;
	int i;

	if ( !PyArg_Parse(args, "(s#i)",
			  &cp, &len, &size) )
		return 0;

	if ( size != 1 && size != 2 && size != 4) {
		PyErr_SetString(AudioopError, "Size should be 1, 2 or 4");
		return 0;
	}
    
	rv = PyString_FromStringAndSize(NULL, len*size);
	if ( rv == 0 )
		return 0;
	ncp = (signed char *)PyString_AsString(rv);
    
	for ( i=0; i < len*size; i += size ) {
		cval = *cp++;
		val = st_ulaw_to_linear(cval);
	
		if ( size == 1 )      *CHARP(ncp, i) = (signed char)(val >> 8);
		else if ( size == 2 ) *SHORTP(ncp, i) = (short)(val);
		else if ( size == 4 ) *LONGP(ncp, i) = (Py_Int32)(val<<16);
	}
	return rv;
}

static PyObject *
audioop_lin2adpcm(self, args)
	PyObject *self;
        PyObject *args;
{
	signed char *cp;
	signed char *ncp;
	int len, size, val = 0, step, valpred, delta,
		index, sign, vpdiff, diff;
	PyObject *rv, *state, *str;
	int i, outputbuffer = 0, bufferstep;

	if ( !PyArg_Parse(args, "(s#iO)",
			  &cp, &len, &size, &state) )
		return 0;
    

	if ( size != 1 && size != 2 && size != 4) {
		PyErr_SetString(AudioopError, "Size should be 1, 2 or 4");
		return 0;
	}
    
	str = PyString_FromStringAndSize(NULL, len/(size*2));
	if ( str == 0 )
		return 0;
	ncp = (signed char *)PyString_AsString(str);

	/* Decode state, should have (value, step) */
	if ( state == Py_None ) {
		/* First time, it seems. Set defaults */
		valpred = 0;
		step = 7;
		index = 0;
	} else if ( !PyArg_Parse(state, "(ii)", &valpred, &index) )
		return 0;

	step = stepsizeTable[index];
	bufferstep = 1;

	for ( i=0; i < len; i += size ) {
		if ( size == 1 )      val = ((int)*CHARP(cp, i)) << 8;
		else if ( size == 2 ) val = (int)*SHORTP(cp, i);
		else if ( size == 4 ) val = ((int)*LONGP(cp, i)) >> 16;

		/* Step 1 - compute difference with previous value */
		diff = val - valpred;
		sign = (diff < 0) ? 8 : 0;
		if ( sign ) diff = (-diff);

		/* Step 2 - Divide and clamp */
		/* Note:
		** This code *approximately* computes:
		**    delta = diff*4/step;
		**    vpdiff = (delta+0.5)*step/4;
		** but in shift step bits are dropped. The net result of this
		** is that even if you have fast mul/div hardware you cannot
		** put it to good use since the fixup would be too expensive.
		*/
		delta = 0;
		vpdiff = (step >> 3);
	
		if ( diff >= step ) {
			delta = 4;
			diff -= step;
			vpdiff += step;
		}
		step >>= 1;
		if ( diff >= step  ) {
			delta |= 2;
			diff -= step;
			vpdiff += step;
		}
		step >>= 1;
		if ( diff >= step ) {
			delta |= 1;
			vpdiff += step;
		}

		/* Step 3 - Update previous value */
		if ( sign )
			valpred -= vpdiff;
		else
			valpred += vpdiff;

		/* Step 4 - Clamp previous value to 16 bits */
		if ( valpred > 32767 )
			valpred = 32767;
		else if ( valpred < -32768 )
			valpred = -32768;

		/* Step 5 - Assemble value, update index and step values */
		delta |= sign;
	
		index += indexTable[delta];
		if ( index < 0 ) index = 0;
		if ( index > 88 ) index = 88;
		step = stepsizeTable[index];

		/* Step 6 - Output value */
		if ( bufferstep ) {
			outputbuffer = (delta << 4) & 0xf0;
		} else {
			*ncp++ = (delta & 0x0f) | outputbuffer;
		}
		bufferstep = !bufferstep;
	}
	rv = Py_BuildValue("(O(ii))", str, valpred, index);
	Py_DECREF(str);
	return rv;
}

static PyObject *
audioop_adpcm2lin(self, args)
	PyObject *self;
        PyObject *args;
{
	signed char *cp;
	signed char *ncp;
	int len, size, valpred, step, delta, index, sign, vpdiff;
	PyObject *rv, *str, *state;
	int i, inputbuffer = 0, bufferstep;

	if ( !PyArg_Parse(args, "(s#iO)",
			  &cp, &len, &size, &state) )
		return 0;

	if ( size != 1 && size != 2 && size != 4) {
		PyErr_SetString(AudioopError, "Size should be 1, 2 or 4");
		return 0;
	}
    
	/* Decode state, should have (value, step) */
	if ( state == Py_None ) {
		/* First time, it seems. Set defaults */
		valpred = 0;
		step = 7;
		index = 0;
	} else if ( !PyArg_Parse(state, "(ii)", &valpred, &index) )
		return 0;
    
	str = PyString_FromStringAndSize(NULL, len*size*2);
	if ( str == 0 )
		return 0;
	ncp = (signed char *)PyString_AsString(str);

	step = stepsizeTable[index];
	bufferstep = 0;
    
	for ( i=0; i < len*size*2; i += size ) {
		/* Step 1 - get the delta value and compute next index */
		if ( bufferstep ) {
			delta = inputbuffer & 0xf;
		} else {
			inputbuffer = *cp++;
			delta = (inputbuffer >> 4) & 0xf;
		}

		bufferstep = !bufferstep;

		/* Step 2 - Find new index value (for later) */
		index += indexTable[delta];
		if ( index < 0 ) index = 0;
		if ( index > 88 ) index = 88;

		/* Step 3 - Separate sign and magnitude */
		sign = delta & 8;
		delta = delta & 7;

		/* Step 4 - Compute difference and new predicted value */
		/*
		** Computes 'vpdiff = (delta+0.5)*step/4', but see comment
		** in adpcm_coder.
		*/
		vpdiff = step >> 3;
		if ( delta & 4 ) vpdiff += step;
		if ( delta & 2 ) vpdiff += step>>1;
		if ( delta & 1 ) vpdiff += step>>2;

		if ( sign )
			valpred -= vpdiff;
		else
			valpred += vpdiff;

		/* Step 5 - clamp output value */
		if ( valpred > 32767 )
			valpred = 32767;
		else if ( valpred < -32768 )
			valpred = -32768;

		/* Step 6 - Update step value */
		step = stepsizeTable[index];

		/* Step 6 - Output value */
		if ( size == 1 ) *CHARP(ncp, i) = (signed char)(valpred >> 8);
		else if ( size == 2 ) *SHORTP(ncp, i) = (short)(valpred);
		else if ( size == 4 ) *LONGP(ncp, i) = (Py_Int32)(valpred<<16);
	}

	rv = Py_BuildValue("(O(ii))", str, valpred, index);
	Py_DECREF(str);
	return rv;
}

static PyMethodDef audioop_methods[] = {
	{ "max", audioop_max },
	{ "minmax", audioop_minmax },
	{ "avg", audioop_avg },
	{ "maxpp", audioop_maxpp },
	{ "avgpp", audioop_avgpp },
	{ "rms", audioop_rms },
	{ "findfit", audioop_findfit },
	{ "findmax", audioop_findmax },
	{ "findfactor", audioop_findfactor },
	{ "cross", audioop_cross },
	{ "mul", audioop_mul },
	{ "add", audioop_add },
	{ "bias", audioop_bias },
	{ "ulaw2lin", audioop_ulaw2lin },
	{ "lin2ulaw", audioop_lin2ulaw },
	{ "lin2lin", audioop_lin2lin },
	{ "adpcm2lin", audioop_adpcm2lin },
	{ "lin2adpcm", audioop_lin2adpcm },
	{ "tomono", audioop_tomono },
	{ "tostereo", audioop_tostereo },
	{ "getsample", audioop_getsample },
	{ "reverse", audioop_reverse },
	{ "ratecv", audioop_ratecv, 1 },
	{ 0,          0 }
};

DL_EXPORT(void)
initaudioop()
{
	PyObject *m, *d;
	m = Py_InitModule("audioop", audioop_methods);
	d = PyModule_GetDict(m);
	AudioopError = PyErr_NewException("audioop.error", NULL, NULL);
	if (AudioopError != NULL)
	     PyDict_SetItemString(d,"error",AudioopError);
}