// Exponential Decay
//
// decay_exponential -  edecay
//
// DESCRIPTION
//
// Inputs:    1
// Outputs:   1
// Constants: 0


#include <math.h>
#include "ts.h"


typedef struct {
    uint_t k;
} ts_decay_exponential_params_t;

ts_parameter_t const ts_decay_exponential_p = { .n_inputs = 1, .n_outputs = 1, .n_constants = 1, .params_size = sizeof(ts_decay_exponential_params_t) };


uint_t ts_decay_exponential_offset( ts_constant_t const *c )
{
	( void )c;
	return ( c ? ((ts_decay_exponential_params_t *)c)->k : 0 );
}

int ts_decay_exponential(
	fp_t * const *y, uint_t y_n,
	fp_t const * const *x, uint_t x_n,
	uint_t n, ts_constant_t const *c
)
{
	TS_PROLOGUE( ts_decay_exponential_p );
	if ( !c ) return -1;
	uint_t k = ((ts_decay_exponential_params_t *)c)->k;
	if (k == 0 || n <= k) return -1;

	fp_t a = ( fp_t ) 1.0 - _ts_reciprocal( k );

	for( uint_t i = 0; i < k; ++i )
		y[0][i] = 0;

	fp_t prev = x[0][0];
	for( uint_t i = 1; i <= k; ++i )
		prev = fmax( x[0][i], prev * a );
	y[0][k] = prev;

	for( uint_t i = k + 1; i < n; ++i )
	{
		y[0][i] = fmax( x[0][i], y[0][i - 1] * a );
	}
	return 0;
}