// Sigmoid
//
// sigmoid - sig
//
// f(x) = ( L / ( 1 + e^( -( 4m * ( x - x_0 ) / L ) ) ) ) + b - ( L / 2 )
//
// m = f'(0)
// b = f(0)
// ( b - ( L / 2 ) ) < y < ( b + ( L / 2 ) )
//
// X_n - 1
// Y_n - 1
// C_n - 3
//
// c[0] = m
// c[1] = L
// c[2] = b


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


typedef struct {
    fp_t m;
    fp_t L;
    fp_t b;
} ts_sigmoid_params_t;

ts_parameter_t const ts_sigmoid_p = { .n_inputs = 1, .n_outputs = 1, .n_constants = 3, .params_size = sizeof(ts_sigmoid_params_t) };


uint_t ts_sigmoid_offset( ts_constant_t const *c )
{
	( void )c;
	return ( 0 );
}

int ts_sigmoid(
	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_sigmoid_p );
	if ( !c ) return -1;
	fp_t m = ((ts_sigmoid_params_t const *)c)->m;
	fp_t L = ((ts_sigmoid_params_t const *)c)->L;
	fp_t b = ((ts_sigmoid_params_t const *)c)->b;

	if (L == 0 || isnan(L) || isinf(L) || isnan(m) || isinf(m)) return -1;
	m = -( 4.0 * m ) / L;
    b = b - ( 0.5 * L );

	for( uint_t i = 0; i < n; ++i )
	{
		fp_t xv = m * x[0][i];
		if( xv > 500.0 ) { y[0][i] = b; continue; }
		if( xv < -500.0 ) { y[0][i] = L + b; continue; }
		y[0][i] = ( L / ( 1.0 + exp( xv ) ) ) + b;
	}
	return 0;
}