100 lines
2.2 KiB
JavaScript
100 lines
2.2 KiB
JavaScript
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/**
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* @license Apache-2.0
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*
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* Copyright (c) 2018 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 = 4;
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// MAIN //
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/**
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* Multiplies a vector `x` by a constant and adds the result to `y`.
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*
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* @param {PositiveInteger} N - number of elements
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* @param {number} alpha - scalar
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* @param {Float64Array} x - input array
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* @param {integer} strideX - `x` stride length
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* @param {Float64Array} y - destination array
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* @param {integer} strideY - `y` stride length
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* @returns {Float64Array} `y`
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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 ] );
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* var y = new Float64Array( [ 1.0, 1.0, 1.0, 1.0, 1.0 ] );
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* var alpha = 5.0;
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*
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* daxpy( x.length, alpha, x, 1, y, 1 );
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* // y => <Float64Array>[ 6.0, 11.0, 16.0, 21.0, 26.0 ]
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*/
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function daxpy( N, alpha, x, strideX, y, strideY ) {
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var ix;
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var iy;
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var m;
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var i;
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if ( N <= 0 || alpha === 0.0 ) {
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return y;
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}
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// Use unrolled loops if both strides are equal to `1`...
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if ( strideX === 1 && strideY === 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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y[ i ] += alpha * x[ i ];
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}
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}
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if ( N < M ) {
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return y;
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}
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for ( i = m; i < N; i += M ) {
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y[ i ] += alpha * x[ i ];
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y[ i+1 ] += alpha * x[ i+1 ];
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y[ i+2 ] += alpha * x[ i+2 ];
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y[ i+3 ] += alpha * x[ i+3 ];
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}
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return y;
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}
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if ( strideX < 0 ) {
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ix = (1-N) * strideX;
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} else {
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ix = 0;
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}
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if ( strideY < 0 ) {
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iy = (1-N) * strideY;
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} else {
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iy = 0;
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}
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for ( i = 0; i < N; i++ ) {
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y[ iy ] += alpha * x[ ix ];
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ix += strideX;
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iy += strideY;
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}
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return y;
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}
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// EXPORTS //
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module.exports = daxpy;
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