81 lines
1.9 KiB
JavaScript
81 lines
1.9 KiB
JavaScript
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/**
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* @license Apache-2.0
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*
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* Copyright (c) 2020 The Stdlib Authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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'use strict';
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// MODULES //
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var sqrt = require( '@stdlib/math/base/special/sqrt' );
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var abs = require( '@stdlib/math/base/special/abs' );
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var pow = require( '@stdlib/math/base/special/pow' );
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var float64ToFloat32 = require( '@stdlib/number/float64/base/to-float32' );
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// MAIN //
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/**
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* Computes the L2-norm of a single-precision floating-point vector.
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*
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* @param {PositiveInteger} N - number of values over which to compute the L2-norm
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* @param {Float32Array} x - input array
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* @param {PositiveInteger} stride - stride length
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* @returns {number} L2-norm
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*
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* @example
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* var Float32Array = require( '@stdlib/array/float32' );
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*
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* var x = new Float32Array( [ 1.0, -2.0, 2.0 ] );
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* var N = 3;
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*
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* var z = snrm2( N, x, 1 );
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* // returns 3.0
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*/
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function snrm2( N, x, stride ) {
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var scale;
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var ssq;
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var ax;
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var i;
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if ( N <= 0 || stride <= 0 ) {
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return 0.0;
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}
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if ( N === 1 ) {
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return abs( x[ 0 ] );
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}
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scale = 0.0;
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ssq = 1.0;
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N *= stride;
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for ( i = 0; i < N; i += stride ) {
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if ( x[ i ] !== 0.0 ) {
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ax = abs( x[ i ] );
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if ( scale < ax ) {
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ssq = float64ToFloat32( 1.0 + ( ssq * pow( scale/ax, 2 ) ) );
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scale = ax;
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} else {
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ssq = float64ToFloat32( ssq + pow( ax/scale, 2 ) );
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}
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}
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}
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return float64ToFloat32( scale * sqrt( ssq ) );
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}
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// EXPORTS //
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module.exports = snrm2;
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