// Chebyshev Polynomial of the First Kind
//
// chebyshev_t - T_n(x)
//
// T_0 = 1, T_1 = x, T_n = 2x*T_(n-1) - T_(n-2)
//
// Inputs:    2 (x, n)
// Outputs:   1 (T_n(x))
// Constants: 0

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


ts_parameter_t const ts_chebyshev_t_p = { .n_inputs = 2, .n_outputs = 1, .n_constants = 0, .params_size = 0 };

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

int ts_chebyshev_t(
	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_chebyshev_t_p );
	(void)c;
    for( uint_t i = 0; i < n; ++i )
    {
        fp_t xv = x[0][i];
        uint_t n_val = (uint_t)x[1][i];
        if (x[1][i] < 0 || x[1][i] > 10000) { y[0][i] = 0; continue; }
        if( n_val == 0 )
        {
            y[0][i] = 1.0;
        }
        else if( n_val == 1 )
        {
            y[0][i] = xv;
        }
        else
        {
            fp_t t0 = 1.0;
            fp_t t1 = xv;
            for( uint_t k = 2; k <= n_val; ++k )
            {
                fp_t t2 = 2.0 * xv * t1 - t0;
                t0 = t1;
                t1 = t2;
            }
            y[0][i] = t1;
        }
    }
	return 0;
}