// Binomial Coefficient
//
// binomial - C(n, k)
//
// Number of combinations: C(n, k) = n! / (k! * (n-k)!)
//
// Inputs:    2 (n, k)
// Outputs:   1 (coefficient)
// Constants: 0

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


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

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

int ts_binomial(
	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_binomial_p );
	(void)c;
    /* C(n, k) = n! / (k! * (n-k)!) */
    for (uint_t i = 0; i < n; ++i)
    {
        fp_t n_val = floor(x[0][i]);
        fp_t k_val = floor(x[1][i]);

        if (k_val > n_val || k_val < 0 || n_val < 0)
        {
            y[0][i] = 0;
            continue;
        }

        /* Use symmetry: C(n,k) = C(n, n-k) */
        if (k_val > n_val - k_val)
            k_val = n_val - k_val;

        fp_t result = 1;
        for (uint_t j = 0; j < (uint_t)k_val; ++j)
        {
            result = result * (n_val - j) / (j + 1);
        }
        y[0][i] = result;
    }
	return 0;
}