/*
 * ECHO_CAN_MG2
 *
 * by Michael Gernoth
 *
 * Based upon kb1ec.h and mec2.h
 * 
 * Copyright (C) 2002, Digium, Inc.
 *
 * This program is free software and may be used and
 * distributed according to the terms of the GNU
 * General Public License, incorporated herein by
 * reference.
 *
 * Additional background on the techniques used in this code can be found in:
 *
 *  Messerschmitt, David; Hedberg, David; Cole, Christopher; Haoui, Amine; 
 *  Winship, Peter; "Digital Voice Echo Canceller with a TMS32020," 
 *  in Digital Signal Processing Applications with the TMS320 Family, 
 *  pp. 415-437, Texas Instruments, Inc., 1986. 
 *
 * A pdf of which is available by searching on the document title at http://www.ti.com/
 *
 */

#ifndef _MG2_ECHO_H
#define _MG2_ECHO_H

#ifdef __KERNEL__
#include <linux/kernel.h>
#include <linux/slab.h>
#define MALLOC(a) kmalloc((a), GFP_KERNEL)
#define FREE(a) kfree(a)
#else
#include <stdlib.h>
#include <unistd.h>
#include <stdint.h>
#include <string.h>
#include <math.h>
#define MALLOC(a) malloc(a)
#define FREE(a) free(a)
#endif


#define ABS(a) abs(a!=-32768?a:-32767)

#define RESTORE_COEFFS {\
				int x;\
				memcpy(ec->a_i, ec->c_i, ec->N_d*sizeof(int));\
				for (x=0;x<ec->N_d;x++) {\
					ec->a_s[x] = ec->a_i[x] >> 16;\
				}\
				ec->backup = BACKUP;\
			}

/* Uncomment to provide summary statistics for overall echo can performance every 4000 samples */ 
/* #define MEC2_STATS 4000 */

/* Uncomment to generate per-sample statistics - this will severely degrade system performance and audio quality */
/* #define MEC2_STATS_DETAILED */

/* Uncomment to generate per-call DC bias offset messages */
/* #define MEC2_DCBIAS_MESSAGE */

/* Get optimized routines for math */
#include "arith.h"

/* Bring in definitions for the various constants and thresholds */
#include "mg2ec_const.h"

#define DC_NORMALIZE

#ifndef NULL
#define NULL 0
#endif
#ifndef FALSE
#define FALSE 0
#endif
#ifndef TRUE
#define TRUE (!FALSE)
#endif

/* Generic circular buffer definition */
typedef struct {
	/* Pointer to the relative 'start' of the buffer */
	int idx_d;
	/* The absolute size of the buffer */
	int size_d;			 
	/* The actual sample -  twice as large as we need, however we do store values at idx_d and idx_d+size_d */
	short *buf_d;			
} echo_can_cb_s;

/* Echo canceller definition */
struct echo_can_state {
	/* an arbitrary ID for this echo can - this really should be settable from the calling channel... */
	int id;

	/* absolute time - aka. sample number index - essentially the number of samples since this can was init'ed */
	int i_d;
  
	/* Pre-computed constants */
	/* ---------------------- */
	/* Number of filter coefficents */
	int N_d;
	/* Rate of adaptation of filter */
	int beta2_i;

	/* Accumulators for power computations */
	/* ----------------------------------- */
	/* reference signal power estimate - aka. Average absolute value of y(k) */
	int Ly_i;			
	/* ... */
	int Lu_i;

	/* Accumulators for signal detectors */
	/* --------------------------------- */
	/* Power estimate of the recent past of the near-end hybrid signal - aka. Short-time average of: 2 x |s(i)| */
	int s_tilde_i;		
	/* Power estimate of the recent past of the far-end receive signal - aka. Short-time average of:     |y(i)| */
	int y_tilde_i;

	/* Near end speech detection counter - stores Hangover counter time remaining, in samples */
	int HCNTR_d;			
  
	/* Circular buffers and coefficients */
	/* --------------------------------- */
	/* ... */
	int *a_i;
	/* ... */
	short *a_s;
	/* Backups */
	int *b_i;
	int *c_i;
	/* Reference samples of far-end receive signal */
	echo_can_cb_s y_s;
	/* Reference samples of near-end signal */
	echo_can_cb_s s_s;
	/* Reference samples of near-end signal minus echo estimate */
	echo_can_cb_s u_s;
	/* Reference samples of far-end receive signal used to calculate short-time average */
	echo_can_cb_s y_tilde_s;

	/* Peak far-end receive signal */
	/* --------------------------- */
	/* Highest y_tilde value in the sample buffer */
	short max_y_tilde;
	/* Index of the sample containing the max_y_tilde value */
	int max_y_tilde_pos;

#ifdef MEC2_STATS
	/* Storage for performance statistics */
	int cntr_nearend_speech_frames;
	int cntr_residualcorrected_frames;
	int cntr_residualcorrected_framesskipped;
	int cntr_coeff_updates;
	int cntr_coeff_missedupdates;
 
	int avg_Lu_i_toolow; 
	int avg_Lu_i_ok;
#endif 
	short lastsig;
	int lastcount;
	int backup;
#ifdef DC_NORMALIZE
	int dc_estimate;
#endif

};

static inline void init_cb_s(echo_can_cb_s *cb, int len, void *where)
{
	cb->buf_d = (short *)where;
	cb->idx_d = 0;
	cb->size_d = len;
}

static inline void add_cc_s(echo_can_cb_s *cb, short newval)
{
	/* Can't use modulus because N+M isn't a power of two (generally) */
	cb->idx_d--;
	if (cb->idx_d < (int)0) 
		/* Whoops - the pointer to the 'start' wrapped around so reset it to the top of the buffer */
	 	cb->idx_d += cb->size_d;
  	
	/* Load two copies into memory */
	cb->buf_d[cb->idx_d] = newval;
	cb->buf_d[cb->idx_d + cb->size_d] = newval;
}

static inline short get_cc_s(echo_can_cb_s *cb, int pos)
{
	/* Load two copies into memory */
	return cb->buf_d[cb->idx_d + pos];
}

static inline void init_cc(struct echo_can_state *ec, int N, int maxy, int maxu) 
{

	void *ptr = ec;
	unsigned long tmp;
	/* Double-word align past end of state */
	ptr += sizeof(struct echo_can_state);
	tmp = (unsigned long)ptr;
	tmp += 3;
	tmp &= ~3L;
	ptr = (void *)tmp;

	/* Reset parameters */
	ec->N_d = N;
	ec->beta2_i = DEFAULT_BETA1_I;
  
	/* Allocate coefficient memory */
	ec->a_i = ptr;
	ptr += (sizeof(int) * ec->N_d);
	ec->a_s = ptr;
	ptr += (sizeof(short) * ec->N_d);

	/* Allocate backup memory */
	ec->b_i = ptr;
	ptr += (sizeof(int) * ec->N_d);
	ec->c_i = ptr;
	ptr += (sizeof(int) * ec->N_d);

	/* Reset Y circular buffer (short version) */
	init_cb_s(&ec->y_s, maxy, ptr);
	ptr += (sizeof(short) * (maxy) * 2);
  
	/* Reset Sigma circular buffer (short version for FIR filter) */
	init_cb_s(&ec->s_s, (1 << DEFAULT_ALPHA_ST_I), ptr);
	ptr += (sizeof(short) * (1 << DEFAULT_ALPHA_ST_I) * 2);

	init_cb_s(&ec->u_s, maxu, ptr);
	ptr += (sizeof(short) * maxu * 2);

	/* Allocate a buffer for the reference signal power computation */
	init_cb_s(&ec->y_tilde_s, ec->N_d, ptr);

	/* Reset the absolute time index */
	ec->i_d = (int)0;
  
	/* Reset the power computations (for y and u) */
	ec->Ly_i = DEFAULT_CUTOFF_I;
	ec->Lu_i = DEFAULT_CUTOFF_I;

#ifdef MEC2_STATS
	/* set the identity */
	ec->id = (int)&ptr;
  
	/* Reset performance stats */
	ec->cntr_nearend_speech_frames = (int)0;
	ec->cntr_residualcorrected_frames = (int)0;
	ec->cntr_residualcorrected_framesskipped = (int)0;
	ec->cntr_coeff_updates = (int)0;
	ec->cntr_coeff_missedupdates = (int)0;

	ec->avg_Lu_i_toolow = (int)0;
	ec->avg_Lu_i_ok = (int)0;
#endif

	/* Reset the near-end speech detector */
	ec->s_tilde_i = (int)0;
	ec->y_tilde_i = (int)0;
	ec->HCNTR_d = (int)0;

}

static inline void echo_can_free(struct echo_can_state *ec)
{
#if defined(DC_NORMALIZE) && defined(MEC2_DCBIAS_MESSAGE)
	printk("EC: DC bias calculated: %d V\n", ec->dc_estimate >> 15);
#endif
	FREE(ec);
}

#ifdef DC_NORMALIZE
short inline dc_removal(int *dc_estimate, short samp)
{
	*dc_estimate += ((((int)samp << 15) - *dc_estimate) >> 9);
	return samp - (*dc_estimate >> 15);
}
#endif

static inline short echo_can_update(struct echo_can_state *ec, short iref, short isig) 
{

	/* Declare local variables that are used more than once */
	/* ... */
	int k;
	/* ... */
	int rs;
	/* ... */
	short u;
	/* ... */
	int Py_i;
	/* ... */
	int two_beta_i;

#ifdef DC_NORMALIZE
	isig = dc_removal(&ec->dc_estimate, isig);
#endif
	
	/* flow A on pg. 428 */
	/* eq. (16): high-pass filter the input to generate the next value;
	 *           push the current value into the circular buffer
	 *
	 * sdc_im1_d = sdc_d;
	 *     sdc_d = sig;
	 *     s_i_d = sdc_d;
	 *       s_d = s_i_d;
	 *     s_i_d = (float)(1.0 - gamma_d) * s_i_d
	 *	+ (float)(0.5 * (1.0 - gamma_d)) * (sdc_d - sdc_im1_d); 
	 */

	/* Update the Far-end receive signal circular buffers and accumulators */
	/* ------------------------------------------------------------------- */
	/* Delete the oldest sample from the power estimate accumulator */
	ec->y_tilde_i -= abs(get_cc_s(&ec->y_s, (1 << DEFAULT_ALPHA_YT_I) - 1 )) >> DEFAULT_ALPHA_YT_I;
	/* Add the new sample to the power estimate accumulator */
	ec->y_tilde_i += abs(iref) >> DEFAULT_ALPHA_ST_I;
	/* Push a copy of the new sample into its circular buffer */
	add_cc_s(&ec->y_s, iref);
 

	/* eq. (2): compute r in fixed-point */
	rs = CONVOLVE2(ec->a_s, 
  			ec->y_s.buf_d + ec->y_s.idx_d, 
  			ec->N_d);
	rs >>= 15;

	if (ec->lastsig == isig) {
		ec->lastcount++;
	} else {
		ec->lastcount = 0;
		ec->lastsig = isig;
	}

	if (isig == 0) {
		u = 0;
	} else if (ec->lastcount > 255) {
		/* We have seen the same input-signal more than 255 times,
		 * we should pass it through uncancelled, as we are likely on hold */
		u = isig;
	} else {
		if (rs < -32768) {
			rs = -32768;
			ec->HCNTR_d = DEFAULT_HANGT;
			RESTORE_COEFFS;
		} else if (rs > 32767) {
			rs = 32767;
			ec->HCNTR_d = DEFAULT_HANGT;
			RESTORE_COEFFS;
		}

		if (ABS(ABS(rs)-ABS(isig)) > MAX_SIGN_ERROR)
		{
			rs = 0;
			RESTORE_COEFFS;
		}

		/* eq. (3): compute the output value (see figure 3) and the error
		 * note: the error is the same as the output signal when near-end
		 * speech is not present
		 */
		u = isig - rs;

		if (u / isig < 0)
			u = isig - (rs >> 1);
	}

	/* Push a copy of the output value sample into its circular buffer */
	add_cc_s(&ec->u_s, u);

	if (!ec->backup) {
		/* Backup coefficients periodically */
		ec->backup = BACKUP;
		memcpy(ec->c_i,ec->b_i,ec->N_d*sizeof(int));
		memcpy(ec->b_i,ec->a_i,ec->N_d*sizeof(int));
	} else
		ec->backup--;


	/* Update the Near-end hybrid signal circular buffers and accumulators */
	/* ------------------------------------------------------------------- */
	/* Delete the oldest sample from the power estimate accumulator */
	ec->s_tilde_i -= abs(get_cc_s(&ec->s_s, (1 << DEFAULT_ALPHA_ST_I) - 1 ));
	/* Add the new sample to the power estimate accumulator */
	ec->s_tilde_i += abs(isig);
	/* Push a copy of the new sample into it's circular buffer */
	add_cc_s(&ec->s_s, isig);


	/* Push a copy of the current short-time average of the far-end receive signal into it's circular buffer */
	add_cc_s(&ec->y_tilde_s, ec->y_tilde_i);		

	/* flow B on pg. 428 */
  
	/* If the hangover timer isn't running then compute the new convergence factor, otherwise set Py_i to 32768 */
	if (!ec->HCNTR_d) {
		Py_i = (ec->Ly_i >> DEFAULT_SIGMA_LY_I) * (ec->Ly_i >> DEFAULT_SIGMA_LY_I);
		Py_i >>= 15;
	} else {
	  	Py_i = (1 << 15);
	}
  
#if 0
	/* Vary rate of adaptation depending on position in the file
	 *  Do not do this for the first (DEFAULT_UPDATE_TIME) secs after speech
	 *  has begun of the file to allow the echo cancellor to estimate the
	 *  channel accurately
	 * Still needs conversion!
	 */

	if (ec->start_speech_d != 0 ){
		if ( ec->i_d > (DEFAULT_T0 + ec->start_speech_d)*(SAMPLE_FREQ) ){
			ec->beta2_d = max_cc_float(MIN_BETA, DEFAULT_BETA1 * exp((-1/DEFAULT_TAU)*((ec->i_d/(float)SAMPLE_FREQ) - DEFAULT_T0 - ec->start_speech_d)));
		}
	} else {
		ec->beta2_d = DEFAULT_BETA1;
	}
#endif
  
	/* Fixed point, inverted */
	ec->beta2_i = DEFAULT_BETA1_I;	
  
	/* Fixed point version, inverted */
	two_beta_i = (ec->beta2_i * Py_i) >> 15;	
	if (!two_beta_i)
		two_beta_i++;

	/* Update the Suppressed signal power estimate accumulator */
        /* ------------------------------------------------------- */
        /* Delete the oldest sample from the power estimate accumulator */
	ec->Lu_i -= abs(get_cc_s(&ec->u_s, (1 << DEFAULT_SIGMA_LU_I) - 1 )) ;
        /* Add the new sample to the power estimate accumulator */
	ec->Lu_i += abs(u);

	/* Update the Far-end reference signal power estimate accumulator */
        /* -------------------------------------------------------------- */
	/* eq. (10): update power estimate of the reference */
        /* Delete the oldest sample from the power estimate accumulator */
	ec->Ly_i -= abs(get_cc_s(&ec->y_s, (1 << DEFAULT_SIGMA_LY_I) - 1)) ;
        /* Add the new sample to the power estimate accumulator */
	ec->Ly_i += abs(iref);

	if (ec->Ly_i < DEFAULT_CUTOFF_I)
		ec->Ly_i = DEFAULT_CUTOFF_I;


	/* Update the Peak far-end receive signal detected */
        /* ----------------------------------------------- */
	if (ec->y_tilde_i > ec->max_y_tilde) {
		/* New highest y_tilde with full life */
		ec->max_y_tilde = ec->y_tilde_i;
		ec->max_y_tilde_pos = ec->N_d - 1;
	} else if (--ec->max_y_tilde_pos < 0) {
		/* Time to find new max y tilde... */
		ec->max_y_tilde = MAX16(ec->y_tilde_s.buf_d + ec->y_tilde_s.idx_d, ec->N_d, &ec->max_y_tilde_pos);
	}

	/* Determine if near end speech was detected in this sample */
	/* -------------------------------------------------------- */
	if (((ec->s_tilde_i >> (DEFAULT_ALPHA_ST_I - 1)) > ec->max_y_tilde) 
	    && (ec->max_y_tilde > 0))  {
		/* Then start the Hangover counter */
		ec->HCNTR_d = DEFAULT_HANGT;
		RESTORE_COEFFS;
#ifdef MEC2_STATS_DETAILED
		printk(KERN_INFO "Reset near end speech timer with: s_tilde_i %d, stmnt %d, max_y_tilde %d\n", ec->s_tilde_i, (ec->s_tilde_i >> (DEFAULT_ALPHA_ST_I - 1)), ec->max_y_tilde);
#endif
#ifdef MEC2_STATS
		++ec->cntr_nearend_speech_frames;
#endif
	} else if (ec->HCNTR_d > (int)0) {
  		/* otherwise, if it's still non-zero, decrement the Hangover counter by one sample */
#ifdef MEC2_STATS
		++ec->cntr_nearend_speech_frames;
#endif
		ec->HCNTR_d--;
	} 

	/* Update coefficients if no near-end speech in this sample (ie. HCNTR_d = 0)
	 * and we have enough signal to bother trying to update.
	 * --------------------------------------------------------------------------
	 */
	if (!ec->HCNTR_d && 				/* no near-end speech present */
		!(ec->i_d % DEFAULT_M)) {		/* we only update on every DEFAULM_M'th sample from the stream */
  			if (ec->Lu_i > MIN_UPDATE_THRESH_I) {	/* there is sufficient energy above the noise floor to contain meaningful data */
  							/* so loop over all the filter coefficients */
#ifdef USED_COEFFS
				int max_coeffs[USED_COEFFS];
				int *pos;

				if (ec->N_d > USED_COEFFS)
					memset(max_coeffs, 0, USED_COEFFS*sizeof(int));
#endif
#ifdef MEC2_STATS_DETAILED
				printk( KERN_INFO "updating coefficients with: ec->Lu_i %9d\n", ec->Lu_i);
#endif
#ifdef MEC2_STATS
				ec->avg_Lu_i_ok = ec->avg_Lu_i_ok + ec->Lu_i;  
				++ec->cntr_coeff_updates;
#endif
				for (k=0; k < ec->N_d; k++) {
					/* eq. (7): compute an expectation over M_d samples */
					int grad2;
					grad2 = CONVOLVE2(ec->u_s.buf_d + ec->u_s.idx_d,
							  ec->y_s.buf_d + ec->y_s.idx_d + k,
							  DEFAULT_M);
					/* eq. (7): update the coefficient */
					ec->a_i[k] += grad2 / two_beta_i;
					ec->a_s[k] = ec->a_i[k] >> 16;

#ifdef USED_COEFFS
					if (ec->N_d > USED_COEFFS) {
						if (abs(ec->a_i[k]) > max_coeffs[USED_COEFFS-1]) {
							/* More or less insertion-sort... */
							pos = max_coeffs;
							while (*pos > abs(ec->a_i[k]))
								pos++;

							if (*pos > max_coeffs[USED_COEFFS-1])
								memmove(pos+1, pos, (USED_COEFFS-(pos-max_coeffs)-1)*sizeof(int));

							*pos = abs(ec->a_i[k]);
						}
					}
#endif
				}

#ifdef USED_COEFFS
				/* Filter out irrelevant coefficients */
				if (ec->N_d > USED_COEFFS)
					for (k=0; k < ec->N_d; k++)
						if (abs(ec->a_i[k]) < max_coeffs[USED_COEFFS-1])
							ec->a_i[k] = ec->a_s[k] = 0;
#endif
		 	 } else { 
#ifdef MEC2_STATS_DETAILED
				printk( KERN_INFO "insufficient signal to update coefficients ec->Lu_i %5d < %5d\n", ec->Lu_i, MIN_UPDATE_THRESH_I);
#endif
#ifdef MEC2_STATS
				ec->avg_Lu_i_toolow = ec->avg_Lu_i_toolow + ec->Lu_i;  
				++ec->cntr_coeff_missedupdates;
#endif
			}
	}
  
	/* paragraph below eq. (15): if no near-end speech in the sample and 
	 * the reference signal power estimate > cutoff threshold
	 * then perform residual error suppression
	 */
#ifdef MEC2_STATS_DETAILED
	if (ec->HCNTR_d == 0)
		printk( KERN_INFO "possibily correcting frame with ec->Ly_i %9d ec->Lu_i %9d and expression %d\n", ec->Ly_i, ec->Lu_i, (ec->Ly_i/(ec->Lu_i + 1)));
#endif

#ifndef NO_ECHO_SUPPRESSOR
#ifdef AGGRESSIVE_SUPPRESSOR
	if ((ec->HCNTR_d < AGGRESSIVE_HCNTR) && (ec->Ly_i > (ec->Lu_i << 1))) {
		for (k=0; k < RESIDUAL_SUPRESSION_PASSES; k++) {
			u = u * (ec->Lu_i >> DEFAULT_SIGMA_LU_I) / ((ec->Ly_i >> (DEFAULT_SIGMA_LY_I)) + 1);
		}
#ifdef MEC2_STATS_DETAILED
		printk( KERN_INFO "aggresively correcting frame with ec->Ly_i %9d ec->Lu_i %9d expression %d\n", ec->Ly_i, ec->Lu_i, (ec->Ly_i/(ec->Lu_i + 1)));
#endif
#ifdef MEC2_STATS
		++ec->cntr_residualcorrected_frames;
#endif
	}
#else
	if (ec->HCNTR_d == 0) { 
		if ((ec->Ly_i/(ec->Lu_i + 1)) > DEFAULT_SUPPR_I) {
			for (k=0; k < RESIDUAL_SUPRESSION_PASSES; k++) {
	  			u = u * (ec->Lu_i >> DEFAULT_SIGMA_LU_I) / ((ec->Ly_i >> (DEFAULT_SIGMA_LY_I + 2)) + 1);
			}
#ifdef MEC2_STATS_DETAILED
			printk( KERN_INFO "correcting frame with ec->Ly_i %9d ec->Lu_i %9d expression %d\n", ec->Ly_i, ec->Lu_i, (ec->Ly_i/(ec->Lu_i + 1)));
#endif
#ifdef MEC2_STATS
		  	++ec->cntr_residualcorrected_frames;
#endif
		}
#ifdef MEC2_STATS
		else {
       			++ec->cntr_residualcorrected_framesskipped;
		}
#endif
	}
#endif	
#endif  

#if 0
	/* This will generate a non-linear supression factor, once converted */
	if ((ec->HCNTR_d == 0) && 
	   ((ec->Lu_d/ec->Ly_d) < DEFAULT_SUPPR) &&
	    (ec->Lu_d/ec->Ly_d > EC_MIN_DB_VALUE)) { 
	    	suppr_factor = (10 / (float)(SUPPR_FLOOR - SUPPR_CEIL)) * log(ec->Lu_d/ec->Ly_d)
	    			- SUPPR_CEIL / (float)(SUPPR_FLOOR - SUPPR_CEIL);
		u_suppr = pow(10.0, (suppr_factor) * RES_SUPR_FACTOR / 10.0) * u_suppr;
	}
#endif  

#ifdef MEC2_STATS
	/* Periodically dump performance stats */
	if ((ec->i_d % MEC2_STATS) == 0) {
		/* make sure to avoid div0's! */
		if (ec->cntr_coeff_missedupdates > 0)
			ec->avg_Lu_i_toolow = (int)(ec->avg_Lu_i_toolow / ec->cntr_coeff_missedupdates);
		else
			ec->avg_Lu_i_toolow = -1;

		if (ec->cntr_coeff_updates > 0)
			ec->avg_Lu_i_ok = (ec->avg_Lu_i_ok / ec->cntr_coeff_updates);
		else
			ec->avg_Lu_i_ok = -1;

		printk( KERN_INFO "%d: Near end speech: %5d Residuals corrected/skipped: %5d/%5d Coefficients updated ok/low sig: %3d/%3d Lu_i avg ok/low sig %6d/%5d\n", 
			ec->id,
			ec->cntr_nearend_speech_frames, 
			ec->cntr_residualcorrected_frames, ec->cntr_residualcorrected_framesskipped, 
			ec->cntr_coeff_updates, ec->cntr_coeff_missedupdates, 
			ec->avg_Lu_i_ok, ec->avg_Lu_i_toolow);

		ec->cntr_nearend_speech_frames = 0;
		ec->cntr_residualcorrected_frames = 0;
		ec->cntr_residualcorrected_framesskipped = 0;
		ec->cntr_coeff_updates = 0;
		ec->cntr_coeff_missedupdates = 0;
		ec->avg_Lu_i_ok = 0;
		ec->avg_Lu_i_toolow = 0;
	}
#endif

	/* Increment the sample index and return the corrected sample */
	ec->i_d++;
	return u;
}

static inline struct echo_can_state *echo_can_create(int len, int adaption_mode)
{
	struct echo_can_state *ec;
	int maxy;
	int maxu;
	maxy = len + DEFAULT_M;
	maxu = DEFAULT_M;
	if (maxy < (1 << DEFAULT_ALPHA_YT_I))
		maxy = (1 << DEFAULT_ALPHA_YT_I);
	if (maxy < (1 << DEFAULT_SIGMA_LY_I))
		maxy = (1 << DEFAULT_SIGMA_LY_I);
	if (maxu < (1 << DEFAULT_SIGMA_LU_I))
		maxu = (1 << DEFAULT_SIGMA_LU_I);
	ec = (struct echo_can_state *)MALLOC(sizeof(struct echo_can_state) +
									4 + 						/* align */
									sizeof(int) * len +			/* a_i */
									sizeof(short) * len + 		/* a_s */
									sizeof(int) * len +		/* b_i */
									sizeof(int) * len +		/* c_i */
									2 * sizeof(short) * (maxy) +	/* y_s */
									2 * sizeof(short) * (1 << DEFAULT_ALPHA_ST_I) + /* s_s */
									2 * sizeof(short) * (maxu) +		/* u_s */
									2 * sizeof(short) * len);			/* y_tilde_s */
	if (ec) {
		memset(ec, 0, sizeof(struct echo_can_state) +
									4 + 						/* align */
									sizeof(int) * len +			/* a_i */
									sizeof(short) * len + 		/* a_s */
									sizeof(int) * len +		/* b_i */
									sizeof(int) * len +		/* c_i */
									2 * sizeof(short) * (maxy) +	/* y_s */
									2 * sizeof(short) * (1 << DEFAULT_ALPHA_ST_I) + /* s_s */
									2 * sizeof(short) * (maxu) +		/* u_s */
									2 * sizeof(short) * len);			/* y_tilde_s */
		init_cc(ec, len, maxy, maxu);
	}
	return ec;
}

static inline int echo_can_traintap(struct echo_can_state *ec, int pos, short val)
{
	/* Set the hangover counter to the length of the can to 
	 * avoid adjustments occuring immediately after initial forced training 
	 */
	ec->HCNTR_d = ec->N_d << 1;

	if (pos >= ec->N_d) {
		memcpy(ec->b_i,ec->a_i,ec->N_d*sizeof(int));
		memcpy(ec->c_i,ec->a_i,ec->N_d*sizeof(int));
		return 1;
	}

	ec->a_i[pos] = val << 17;
	ec->a_s[pos] = val << 1;

	if (++pos >= ec->N_d) {
		memcpy(ec->b_i,ec->a_i,ec->N_d*sizeof(int));
		memcpy(ec->c_i,ec->a_i,ec->N_d*sizeof(int));
		return 1;
	}

	return 0;
}

#endif