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feat: add stats/strided/selmax
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‎lib/node_modules/@stdlib/stats/strided/selmax/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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# selmax
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> Calculate the maximum value of a strided array by selecting elements according to a mask.
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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 selmax = require( '@stdlib/stats/strided/selmax' );
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```
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#### selmax( N, x, strideX, mask, strideMask )
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Computes the maximum value of a strided array by selecting elements according to a mask.
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```javascript
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var x = [ 1.0, -2.0, 4.0, 2.0 ];
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var mask = [ 1, 1, 0, 1 ];
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var v = selmax( x.length, x, 1, mask, 1 );
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// returns 2.0
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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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- **x**: input [`Array`][mdn-array] or [`typed array`][mdn-typed-array].
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- **strideX**: stride length for `x`.
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- **mask**: mask [`Array`][mdn-array] or [`typed array`][mdn-typed-array]. If a `mask` array element is `true`, the corresponding element in `x` is considered valid and **included** in computation. If a `mask` array element is `false`, the corresponding element in `x` is considered invalid/missing and **excluded** from computation.
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- **strideMask**: stride length for `mask`.
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The `N` and stride parameters determine which elements in the strided arrays are accessed at runtime. For example, to compute the maximum value of every other element in `x`,
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```javascript
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var x = [ 1.0, 2.0, -7.0, -2.0, 4.0, 3.0, 5.0, 6.0 ];
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var mask = [ 1, 1, 1, 1, 1, 1, 0, 0 ];
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var v = selmax( 4, x, 2, mask, 2 );
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// returns 4.0
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```
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Note that indexing is relative to the first index. To introduce offsets, 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 BooleanArray = require( '@stdlib/array/bool' );
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var x0 = new Float64Array( [ 2.0, 1.0, -2.0, -2.0, 3.0, 4.0, 5.0, 6.0 ] );
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var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 );
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var mask0 = new BooleanArray([
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true, true, true, true, true, true, false, false
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]);
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var mask1 = new BooleanArray( mask0.buffer, mask0.BYTES_PER_ELEMENT*1 );
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var v = selmax( 4, x1, 2, mask1, 2 );
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// returns 4.0
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```
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#### selmax.ndarray( N, x, strideX, offsetX, mask, strideMask, offsetMask )
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Computes the maximum value of a strided array by selecting elements according to a mask and using alternative indexing semantics.
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```javascript
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var x = [ 1.0, -2.0, 4.0, 2.0 ];
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var mask = [ 1, 1, 0, 1 ];
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var v = selmax.ndarray( x.length, x, 1, 0, mask, 1, 0 );
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// returns 2.0
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```
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The function has the following additional parameters:
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- **offsetX**: starting index for `x`.
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- **offsetMask**: starting index for `mask`.
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While [`typed array`][mdn-typed-array] views mandate a view offset based on the underlying buffer, the offset parameters support indexing semantics based on starting indices. For example, to calculate the maximum value for every other value in `x` starting from the second value
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```javascript
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var x = [ 2.0, 1.0, -2.0, -2.0, 3.0, 4.0, 5.0, 6.0 ];
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var mask = [ 1, 1, 1, 1, 1, 1, 0, 0 ];
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var v = selmax.ndarray( 4, x, 2, 1, mask, 2, 1 );
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// returns 4.0
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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 `NaN`.
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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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</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 uniform = require( '@stdlib/random/array/uniform' );
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var bernoulli = require( '@stdlib/random/array/bernoulli' );
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var selmax = require( '@stdlib/stats/strided/selmax' );
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var x = uniform( 10, -50.0, 50.0, {
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'dtype': 'float64'
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});
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console.log( x );
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var mask = bernoulli( x.length, 0.8, {
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'dtype': 'generic'
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});
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console.log( mask );
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var v = selmax( x.length, x, 1, mask, 1 );
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console.log( v );
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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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* * *
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## See Also
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- <span class="package-name">[`@stdlib/stats/strided/max`][@stdlib/stats/strided/max]</span><span class="delimiter">: </span><span class="description">calculate the maximum value of a strided array.</span>
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- <span class="package-name">[`@stdlib/stats/strided/mskmax`][@stdlib/stats/strided/mskmax]</span><span class="delimiter">: </span><span class="description">calculate the maximum value of a strided array according to a mask.</span>
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- <span class="package-name">[`@stdlib/stats/strided/nanmax`][@stdlib/stats/strided/nanmax]</span><span class="delimiter">: </span><span class="description">calculate the maximum value of a strided array, ignoring NaN values.</span>
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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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[@stdlib/array/base/accessor]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/array/base/accessor
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[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray
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<!-- <related-links> -->
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[@stdlib/stats/strided/max]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/strided/max
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[@stdlib/stats/strided/mskmax]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/strided/mskmax
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[@stdlib/stats/strided/nanmax]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/strided/nanmax
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<!-- </related-links> -->
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</section>
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<!-- /.links -->

‎lib/node_modules/@stdlib/stats/strided/selmax/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 isnan = require( '@stdlib/math/base/assert/is-nan' );
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var uniform = require( '@stdlib/random/array/uniform' );
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var bernoulli = require( '@stdlib/random/array/bernoulli' );
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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 selmax = require( './../lib' );
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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 mask = bernoulli( len, 0.8, options );
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var x = uniform( len, -10.0, 10.0, 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 v;
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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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v = selmax( x.length, x, 1, mask, 1 );
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if ( isnan( v ) ) {
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b.fail( 'should not return NaN' );
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}
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}
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b.toc();
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if ( isnan( v ) ) {
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b.fail( 'should not return NaN' );
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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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