blas-dnrm2/lib/index.js

Computes the L2 norm (Euclidean norm).

'use strict';

// MODULE //

var abs = require( 'math-abs' );
var sqrt = require( 'math-sqrt' );


// DNRM2 //

/**
* FUNCTION: dnrm2( N, x, stride, offset )
*	Computes the L2 norm.
*
* @param {Number} N - number of accessed elements
* @param {Array|Int8Array|Uint8Array|Uint8ClampedArray|Int16Array|Uint16Array|Int32Array|Uint32Array|Float32Array|Float64Array} x - input array
* @param {Number} stride - specifies how to index into `x`
* @param {Number} offset - specifies where to begin indexing into `x`
* @returns {Number|Void} norm or undefined
*/
function dnrm2( N, x, stride, offset ) {
	var val;
	var ix;
	var i;
	var r;
	var s;
	var t;
	if (
		N < 0 ||
		stride <= 0 ||
		offset < 0
	) {
		return;
	}
	if ( N === 0 ) {
		return 0;
	}
	ix = offset;
	if ( N === 1 ) {
		return abs( x[ ix ] );
	}
	t = 0; // scale
	s = 1; // sum of squares
	for ( i = 0; i < N; i++ ) {
		val = x[ ix ];
		if ( val !== 0 ) {
			val = abs( val );
			if ( val > t ) {
				r = t / val;
				s = 1 + s*r*r;
				t = val;
			} else {
				r = val / t;
				s = s + r*r;
			}
		}
		ix += stride;
	}
	return t * sqrt( s );
} // end FUNCTION dnrm2()


// EXPORTS //

module.exports = dnrm2;