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feat: add blas/ext/base/gwhere
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‎lib/node_modules/@stdlib/blas/ext/base/gwhere/README.md‎

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<!--
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@license Apache-2.0
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Copyright (c) 2026 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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# gwhere
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> Take elements from one of two strided arrays depending on a condition.
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<section class="intro">
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</section>
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<!-- /.intro -->
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<section class="usage">
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## Usage
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```javascript
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var gwhere = require( '@stdlib/blas/ext/base/gwhere' );
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```
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#### gwhere( N, condition, strideC, x, strideX, y, strideY )
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Takes elements from one of two strided arrays depending on a condition.
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```javascript
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var condition = [ 1, 0, 1 ];
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var x = [ 1.0, 2.0, 3.0 ];
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var y = [ 4.0, 5.0, 6.0 ];
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var out = gwhere( 3, condition, 1, x, 1, y, 1 );
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// returns [ 1.0, 5.0, 3.0 ]
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```
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The function has the following parameters:
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- **N**: number of indexed elements.
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- **condition**: condition array.
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- **strideC**: stride length for `condition`.
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- **x**: first input [`Array`][mdn-array] or [`typed array`][mdn-typed-array].
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- **strideX**: stride length for `x`.
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- **y**: second input [`Array`][mdn-array] or [`typed array`][mdn-typed-array].
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- **strideY**: stride length for `y`.
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The `N` and stride parameters determine which elements in the strided arrays are accessed at runtime. For example, to select from every other element:
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```javascript
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var condition = [ 1, 0, 0, 1, 1, 0 ];
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var x = [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ];
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var y = [ 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 ];
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var out = gwhere( 3, condition, 2, x, 2, y, 2 );
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// returns [ 1.0, 9.0, 5.0 ]
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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, max-len -->
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```javascript
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var Float64Array = require( '@stdlib/array/float64' );
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// Initial arrays...
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var condition0 = new Float64Array( [ 0.0, 1.0, 0.0, 1.0, 0.0, 1.0 ] );
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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 condition1 = new Float64Array( condition0.buffer, condition0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
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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*1 ); // start at 2nd element
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var out = gwhere( 3, condition1, 2, x1, 2, y1, 2 );
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// returns [ 2.0, 4.0, 6.0 ]
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```
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<!-- lint disable maximum-heading-length -->
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#### gwhere.ndarray( N, condition, strideC, offsetC, x, strideX, offsetX, y, strideY, offsetY )
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<!-- lint enable maximum-heading-length -->
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Takes elements from one of two strided arrays depending on a condition using alternative indexing semantics.
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```javascript
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var condition = [ 1, 0, 1 ];
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var x = [ 1.0, 2.0, 3.0 ];
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var y = [ 4.0, 5.0, 6.0 ];
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var out = gwhere.ndarray( 3, condition, 1, 0, x, 1, 0, y, 1, 0 );
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// returns [ 1.0, 5.0, 3.0 ]
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```
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The function has the following additional parameters:
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- **offsetC**: starting index for `condition`.
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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, offset parameters support indexing semantics based on starting indices. For example, to select from every other element starting from the second element:
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```javascript
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var condition = [ 0, 1, 0, 0, 0, 1 ];
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var x = [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ];
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var y = [ 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 ];
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var out = gwhere.ndarray( 3, condition, 2, 1, x, 2, 1, y, 2, 1 );
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// returns [ 2.0, 10.0, 6.0 ]
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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 return an empty array.
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- Both functions support array-like objects having getter and setter accessors for array element access (e.g., [`@stdlib/array/base/accessor`][@stdlib/array/base/accessor]).
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- Both functions return a new generic `Array`. To assign results to a specific output array, use [`@stdlib/array/base/where`][@stdlib/array/base/where].
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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 bernoulli = require( '@stdlib/random/array/bernoulli' );
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var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
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var gwhere = require( '@stdlib/blas/ext/base/gwhere' );
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var condition = bernoulli( 20, 0.5, {
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'dtype': 'generic'
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});
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var x = discreteUniform( 20, 0, 100, {
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'dtype': 'generic'
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});
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var y = discreteUniform( 20, -100, 0, {
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'dtype': 'generic'
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});
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console.log( condition );
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console.log( x );
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console.log( y );
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var out = gwhere( condition.length, condition, 1, x, 1, y, 1 );
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console.log( out );
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```
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</section>
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<!-- /.examples -->
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<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->
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<section class="related">
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</section>
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<!-- /.related -->
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<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
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<section class="links">
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[mdn-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array
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[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray
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[@stdlib/array/base/accessor]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/array/base/accessor
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[@stdlib/array/base/where]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/array/base/where
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</section>
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<!-- /.links -->

‎lib/node_modules/@stdlib/blas/ext/base/gwhere/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) 2026 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 bernoulli = require( '@stdlib/random/array/bernoulli' );
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var uniform = require( '@stdlib/random/array/uniform' );
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var isArray = require( '@stdlib/assert/is-array' );
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var pow = require( '@stdlib/math/base/special/pow' );
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var format = require( '@stdlib/string/format' );
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var pkg = require( './../package.json' ).name;
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var gwhere = require( './../lib/main.js' );
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// VARIABLES //
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var options = {
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'dtype': 'generic'
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};
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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 condition = bernoulli( len, 0.5, options );
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var x = uniform( len, -100, 100, options );
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var y = uniform( len, -100, 100, options );
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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 out;
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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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condition[ i%len ] = ( condition[ i%len ] + 1 ) % 2;
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out = gwhere( len, condition, 1, x, 1, y, 1 );
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if ( !isArray( out ) ) {
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b.fail( 'should return an array' );
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}
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}
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b.toc();
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if ( !isArray( out ) ) {
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b.fail( 'should return an array' );
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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( format( '%s:len=%d', pkg, len ), f );
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}
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}
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main();

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