blas-idamax/lib/index.js

Finds the first element equal to the maximum absolute value of x and returns the element index.

'use strict';

// MODULES //

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


// IDAMAX //

/**
* FUNCTION: idamax( N, x, stride, offset )
*	Finds the first element equal to the maximum absolute-value of `x` and returns the element index.
*
* @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} index or undefined
*/
function idamax( N, x, stride, offset ) {
	var max; // max value
	var im;  // max index
	var ix;  // stride index
	var v;   // absolute value
	var i;
	if (
		N <= 0 ||
		stride <= 0 ||
		offset < 0
	) {
		// note that the reference implementation returns an invalid index
		return;
	}
	ix = offset;
	if ( N === 1 ) {
		return 0;
	}
	max = abs( x[ ix ] );
	ix += stride;
	im = 0;
	for ( i = 1; i < N; i++ ) {
		v = abs( x[ ix ] );
		if ( v > max ) {
			max = v;
			im = i;
		}
		ix += stride;
	}
	return im;
} // end FUNCTION idamax()


// EXPORTS //

module.exports = idamax;