ndarray.js (2103B)
1 /** 2 * @license Apache-2.0 3 * 4 * Copyright (c) 2020 The Stdlib Authors. 5 * 6 * Licensed under the Apache License, Version 2.0 (the "License"); 7 * you may not use this file except in compliance with the License. 8 * You may obtain a copy of the License at 9 * 10 * http://www.apache.org/licenses/LICENSE-2.0 11 * 12 * Unless required by applicable law or agreed to in writing, software 13 * distributed under the License is distributed on an "AS IS" BASIS, 14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 15 * See the License for the specific language governing permissions and 16 * limitations under the License. 17 */ 18 19 'use strict'; 20 21 // MODULES // 22 23 var sqrt = require( '@stdlib/math/base/special/sqrt' ); 24 var abs = require( '@stdlib/math/base/special/abs' ); 25 var pow = require( '@stdlib/math/base/special/pow' ); 26 var float64ToFloat32 = require( '@stdlib/number/float64/base/to-float32' ); 27 28 29 // MAIN // 30 31 /** 32 * Computes the L2-norm of a single-precision floating-point vector. 33 * 34 * @param {PositiveInteger} N - number of values over which to compute the L2-norm 35 * @param {Float32Array} x - input array 36 * @param {integer} stride - stride length 37 * @param {NonNegativeInteger} offset - starting index 38 * @returns {number} L2-norm 39 * 40 * @example 41 * var Float32Array = require( '@stdlib/array/float32' ); 42 * var floor = require( '@stdlib/math/base/special/floor' ); 43 * 44 * var x = new Float32Array( [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0 ] ); 45 * var N = floor( x.length / 2 ); 46 * 47 * var z = snrm2( N, x, 2, 1 ); 48 * // returns 5.0 49 */ 50 function snrm2( N, x, stride, offset ) { 51 var scale; 52 var ssq; 53 var ax; 54 var ix; 55 var i; 56 57 if ( N <= 0 ) { 58 return 0.0; 59 } 60 if ( N === 1 ) { 61 return abs( x[ offset ] ); 62 } 63 ix = offset; 64 scale = 0.0; 65 ssq = 1.0; 66 for ( i = 0; i < N; i++ ) { 67 if ( x[ ix ] !== 0.0 ) { 68 ax = abs( x[ ix ] ); 69 if ( scale < ax ) { 70 ssq = float64ToFloat32( 1.0 + ( ssq * pow( scale/ax, 2 ) ) ); 71 scale = ax; 72 } else { 73 ssq = float64ToFloat32( ssq + pow( ax/scale, 2 ) ); 74 } 75 } 76 ix += stride; 77 } 78 return float64ToFloat32( scale * sqrt( ssq ) ); 79 } 80 81 82 // EXPORTS // 83 84 module.exports = snrm2;