92 lines
1.9 KiB
JavaScript
92 lines
1.9 KiB
JavaScript
/**
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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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// VARIABLES //
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var M = 5;
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// MAIN //
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/**
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* Multiplies a vector `x` by a scalar `alpha`.
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*
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* @param {PositiveInteger} N - number of indexed elements
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* @param {number} alpha - scalar
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* @param {Float64Array} x - input array
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* @param {integer} stride - index increment
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* @param {NonNegativeInteger} offset - starting index
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* @returns {Float64Array} input array
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*
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* @example
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* var Float64Array = require( '@stdlib/array/float64' );
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*
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* var x = new Float64Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );
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* var alpha = 5.0;
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*
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* dscal( 3, alpha, x, 1, x.length-3 );
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* // x => <Float64Array>[ 1.0, -2.0, 3.0, -20.0, 25.0, -30.0 ]
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*/
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function dscal( N, alpha, x, stride, offset ) {
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var ix;
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var m;
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var i;
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if ( N <= 0 || alpha === 1.0 ) {
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return x;
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}
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ix = offset;
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// Use loop unrolling if the stride is equal to `1`...
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if ( stride === 1 ) {
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m = N % M;
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// If we have a remainder, run a clean-up loop...
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if ( m > 0 ) {
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for ( i = 0; i < m; i++ ) {
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x[ ix ] *= alpha;
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ix += stride;
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}
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}
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if ( N < M ) {
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return x;
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}
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for ( i = m; i < N; i += M ) {
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x[ ix ] *= alpha;
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x[ ix+1 ] *= alpha;
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x[ ix+2 ] *= alpha;
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x[ ix+3 ] *= alpha;
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x[ ix+4 ] *= alpha;
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ix += M;
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}
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return x;
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}
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for ( i = 0; i < N; i++ ) {
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x[ ix ] *= alpha;
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ix += stride;
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}
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return x;
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}
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// EXPORTS //
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module.exports = dscal;
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