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Add BLAS level 1 routine to interchange vectors
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‎lib/node_modules/@stdlib/blas/base/dswap/README.md

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<!--
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@license Apache-2.0
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Copyright (c) 2020 The Stdlib Authors.
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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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http://www.apache.org/licenses/LICENSE-2.0
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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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# dswap
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> Interchange two vectors.
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<section class="usage">
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## Usage
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```javascript
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var dswap = require( '@stdlib/blas/base/dswap' );
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```
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#### dswap( N, x, strideX, y, strideY )
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Interchanges vectors `x` and `y`.
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```javascript
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var Float64Array = require( '@stdlib/array/float64' );
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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( [ 6.0, 7.0, 8.0, 9.0, 10.0 ] );
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dswap( x.length, x, 1, y, 1 );
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// x => <Float64Array>[ 6.0, 7.0, 8.0, 9.0, 10.0 ]
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// y => <Float64Array>[ 1.0, 2.0, 3.0, 4.0, 5.0 ]
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```
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The function accepts the following parameters:
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- **N**: number of values to swap.
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- **x**: first input [`Float64Array`][mdn-float64array].
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- **strideX**: index increment for `x`.
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- **y**: second input [`Float64Array`][mdn-float64array].
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- **strideY**: index increment for `y`.
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The `N` and `stride` parameters determine how values from `x` are accessed at runtime. For example, to swap in reverse order every other value in `x` with the first `N` elements of `y`,
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```javascript
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var Float64Array = require( '@stdlib/array/float64' );
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var floor = require( '@stdlib/math/base/special/floor' );
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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 y = new Float64Array( [ 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 ] );
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var N = floor( x.length / 2 );
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dswap( N, x, -2, y, 1 );
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// x => <Float64Array>[ 1.0, 7.0, 3.0, 8.0, 5.0, 9.0 ]
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// y => <Float64Array>[ 5.0, 3.0, 1.0, 10.0, 11.0, 12.0 ]
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```
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Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views.
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<!-- eslint-disable stdlib/capitalized-comments -->
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```javascript
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var Float64Array = require( '@stdlib/array/float64' );
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var floor = require( '@stdlib/math/base/special/floor' );
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// Initial arrays...
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var x0 = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );
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var y0 = new Float64Array( [ 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 ] );
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// Create offset views...
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var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
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var y1 = new Float64Array( y0.buffer, y0.BYTES_PER_ELEMENT*3 ); // start at 4th element
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var N = floor( x0.length / 2 );
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// Swap in reverse order every other value from `x1` with `y1`...
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dswap( N, x1, -2, y1, 1 );
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// x0 => <Float64Array>[ 1.0, 12.0, 3.0, 11.0, 5.0, 10.0 ]
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// y0 => <Float64Array>[ 7.0, 8.0, 9.0, 6.0, 4.0, 2.0 ]
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```
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#### dswap.ndarray( N, x, strideX, offsetX, y, strideY, offsetY )
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Interchanges vectors `x` and `y`, with alternative indexing semantics.
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```javascript
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var Float64Array = require( '@stdlib/array/float64' );
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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( [ 6.0, 7.0, 8.0, 9.0, 10.0 ] );
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dswap.ndarray( x.length, x, 1, 0, y, 1, 0 );
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// x => <Float64Array>[ 6.0, 7.0, 8.0, 9.0, 10.0 ]
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// y => <Float64Array>[ 1.0, 2.0, 3.0, 4.0, 5.0 ]
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```
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The function accepts the following additional parameters:
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- **offsetX**: starting index for `x`.
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- **offsetY**: starting index for `y`.
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While [`typed array`][mdn-typed-array] views mandate a view offset based on the underlying `buffer`, the `offsetX` and `offsetY` parameters support indexing semantics based on starting indices. For example, to swap every other value in `x` starting from the second value with the last `N` elements in `y` where `x[i] = y[n]`, `x[i+2] = y[n-1]`,...,
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```javascript
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var Float64Array = require( '@stdlib/array/float64' );
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var floor = require( '@stdlib/math/base/special/floor' );
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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 y = new Float64Array( [ 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 ] );
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var N = floor( x.length / 2 );
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dswap.ndarray( N, x, 2, 1, y, -1, y.length-1 );
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// x => <Float64Array>[ 1.0, 12.0, 11.0, 10.0, 5.0, 6.0 ]
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// y => <Float64Array>[ 7.0, 8.0, 9.0, 6.0, 4.0, 2.0 ]
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```
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</section>
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<!-- /.usage -->
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<section class="notes">
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## Notes
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- If `N <= 0`, both functions leave `x` and `y` unchanged.
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- `dswap()` corresponds to the [BLAS][blas] level 1 function [`dswap`][dswap].
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</section>
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<!-- /.notes -->
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<section class="examples">
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## Examples
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<!-- eslint no-undef: "error" -->
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```javascript
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var randu = require( '@stdlib/random/base/randu' );
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var round = require( '@stdlib/math/base/special/round' );
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var Float64Array = require( '@stdlib/array/float64' );
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var dswap = require( '@stdlib/blas/base/dswap' );
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var x;
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var y;
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var i;
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x = new Float64Array( 10 );
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y = new Float64Array( 10 );
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for ( i = 0; i < x.length; i++ ) {
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x[ i ] = round( randu()*500.0 );
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y[ i ] = round( randu()*255.0 );
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}
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console.log( x );
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console.log( y );
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// Swap elements in `x` and `y` starting from the end of `y`:
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dswap( x.length, x, 1, y, -1 );
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console.log( x );
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console.log( y );
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```
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</section>
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<!-- /.examples -->
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<section class="links">
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[blas]: http://www.netlib.org/blas
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[dswap]: http://www.netlib.org/lapack/explore-html/de/da4/group__double__blas__level1.html
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[mdn-float64array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Float64Array
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[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray
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</section>
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<!-- /.links -->

‎lib/node_modules/@stdlib/blas/base/dswap/benchmark/benchmark.js

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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 bench = require( '@stdlib/bench' );
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var randu = require( '@stdlib/random/base/randu' );
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var isnan = require( '@stdlib/math/base/assert/is-nan' );
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var pow = require( '@stdlib/math/base/special/pow' );
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var Float64Array = require( '@stdlib/array/float64' );
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var pkg = require( './../package.json' ).name;
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var dswap = require( './../lib/main.js' );
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// FUNCTIONS //
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/**
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* Creates a benchmark function.
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*
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* @private
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* @param {PositiveInteger} len - array length
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* @returns {Function} benchmark function
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*/
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function createBenchmark( len ) {
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var x;
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var y;
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var i;
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x = new Float64Array( len );
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y = new Float64Array( len );
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for ( i = 0; i < x.length; i++ ) {
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x[ i ] = ( randu()*10000.0 ) - 20000.0;
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}
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return benchmark;
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/**
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* Benchmark function.
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*
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* @private
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* @param {Benchmark} b - benchmark instance
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*/
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function benchmark( b ) {
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var z;
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var i;
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b.tic();
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for ( i = 0; i < b.iterations; i++ ) {
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z = dswap( x.length, x, 1, y, 1 );
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if ( isnan( z[ i%x.length ] ) ) {
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b.fail( 'something went wrong' );
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}
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}
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b.toc();
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if ( isnan( z[ i%x.length ] ) ) {
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b.fail( 'something went wrong' );
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}
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b.pass( 'benchmark finished' );
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b.end();
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}
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}
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// MAIN //
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/**
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* Main execution sequence.
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*
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* @private
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*/
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function main() {
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var len;
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var min;
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var max;
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var f;
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var i;
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min = 1; // 10^min
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max = 6; // 10^max
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for ( i = min; i <= max; i++ ) {
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len = pow( 10, i );
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f = createBenchmark( len );
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bench( pkg+':len='+len, f );
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}
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}
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main();

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