math-evalpoly/lib/factory.js

Evaluates a polynomial.

/* jshint evil:true */
'use strict';

// EVALPOLY FACTORY //

/**
* FUNCTION: factory( c )
*	Returns a function for evaluating a polynomial.
*
* @param {Number[]|Int8Array|Uint8Array|Uint8ClampedArray|Int16Array|Uint16Array|Int32Array|Uint32Array|Float32Array|Float64Array} c - polynomial coefficients sorted in ascending degree
* @returns {Function} function for evaluating a polynomial
*/
function factory( c ) {
	var f;
	var n;
	var m;
	var i;

	// Code generation. Start with the function definition...
	f = 'return function evalpoly(x){';

	// Create the function body...
	n = c.length;

	// If no coefficients, the function always returns 0...
	if ( n === 0 ) {
		f += 'return 0;';
	}
	// If only one coefficient, the function always returns that coefficient...
	else if ( n === 1 ) {
		f += 'return ' + c[ 0 ] + ';';
	}
	// If more than one coefficient, apply Horner's method...
	else {
		// If `x == 0`, return the first coefficient...
		f += 'if(x===0){return ' + c[ 0 ] + ';}';

		// Otherwise, evaluate the polynomial...
		f += 'return ' + c[ 0 ];
		m = n - 1;
		for ( i = 1; i < n; i++ ) {
			f += '+x*';
			if ( i < m ) {
				f += '(';
			}
			f += c[ i ];
		}
		// Close all the parentheses...
		for ( i = 0; i < m-1; i++ ) {
			f += ')';
		}
		f += ';';
	}
	// Close the function:
	f += '}';

	// Create the function in the global scope:
	return ( new Function( f ) )();

	/**
	* returns
	*	function evalpoly( x ) {
	*		if ( x === 0 ) {
	*			return c[ 0 ];
	*		}
	*		return c[0]+x*(c[1]+x*(c[2]+x*(c[3]+...+x*(c[n-2]+x*c[n-1]))));
	*	}
	*/
} // end FUNCTION factory()


// EXPORTS //

module.exports = factory;