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feat: add math/base/special/factorial2f
PR-URL: #6736 Ref: #649 Co-authored-by: Athan Reines <[email protected]> Reviewed-by: Athan Reines <[email protected]> Reviewed-by: Philipp Burckhardt <[email protected]>
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‎lib/node_modules/@stdlib/math/base/special/factorial2f/README.md

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<!--
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@license Apache-2.0
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Copyright (c) 2025 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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# factorial2f
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> Evaluate the [double factorial][double-factorial] function as a single-precision floating-point number.
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<section class="intro">
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The [double factorial][double-factorial] of a number `n`, denoted `n!!`, is defined as the product of all the positive integers up to `n` that have the same parity (odd or even) as `n`.
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Thus, for example, `5!!` is `5 * 3 * 1 = 15` and `8!!` is `8 * 6 * 4 * 2 = 384`.
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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 factorial2f = require( '@stdlib/math/base/special/factorial2f' );
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```
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#### factorial2f( n )
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Evaluates the [double factorial][double-factorial] of `n` as a single-precision floating-point number.
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```javascript
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var v = factorial2f( 3 );
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// returns 3
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v = factorial2f( 4 );
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// returns 8
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v = factorial2f( 10 );
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// returns 3840
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```
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If `n > 56`, the function returns `NaN`, as larger [double factorial][double-factorial] values cannot be safely represented in [single-precision floating-point format][ieee754].
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```javascript
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var v = factorial2f( 57 );
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// returns Infinity
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```
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If not provided a nonnegative integer value, the function returns `NaN`.
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```javascript
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var v = factorial2f( 3.14 );
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// returns NaN
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v = factorial2f( -1 );
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// returns NaN
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```
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If provided `NaN`, the function returns `NaN`.
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```javascript
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var v = factorial2f( NaN );
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// returns NaN
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```
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</section>
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<!-- /.usage -->
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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 discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
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var logEachMap = require( '@stdlib/console/log-each-map' );
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var factorial2f = require( '@stdlib/math/base/special/factorial2f' );
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var x = discreteUniform( 10, 0, 56, {
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'dtype': 'int32'
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});
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logEachMap( 'factorial2f(%d) = %0.1f', x, factorial2f );
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```
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</section>
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<!-- /.examples -->
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<!-- C interface documentation. -->
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* * *
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<section class="c">
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## C APIs
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<!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. -->
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<section class="intro">
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</section>
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<!-- /.intro -->
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<!-- C usage documentation. -->
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<section class="usage">
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### Usage
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```c
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#include "stdlib/math/base/special/factorial2f.h"
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```
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#### stdlib_base_factorial2f( n )
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Evaluates the [double factorial][double-factorial] of `n` as a single-precision floating-point number.
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```c
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float out = stdlib_base_factorial2f( 3 );
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// returns 3.0f
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```
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The function accepts the following arguments:
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- **n**: `[in] int32_t` input value.
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```c
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float stdlib_base_factorial2f( const int32_t n );
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```
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</section>
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<!-- /.usage -->
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<!-- C API usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
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<section class="notes">
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</section>
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<!-- /.notes -->
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<!-- C API usage examples. -->
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<section class="examples">
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### Examples
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```c
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#include "stdlib/math/base/special/factorial2f.h"
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#include <stdio.h>
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#include <stdint.h>
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int main( void ) {
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const int32_t x[] = { 1, 10, 50, 56, 57 };
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float b;
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int i;
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for ( i = 0; i < 5; i++ ) {
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b = stdlib_base_factorial2f( x[ i ] );
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printf ( "factorial2f(%d) = %f\n", x[ i ], b );
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}
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}
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```
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</section>
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<!-- /.examples -->
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</section>
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<!-- /.c -->
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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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[double-factorial]: https://en.wikipedia.org/wiki/Double_factorial
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[ieee754]: https://en.wikipedia.org/wiki/IEEE_754-1985
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<!-- <related-links> -->
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<!-- </related-links> -->
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</section>
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<!-- /.links -->

‎lib/node_modules/@stdlib/math/base/special/factorial2f/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) 2025 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 isnanf = require( '@stdlib/math/base/assert/is-nanf' );
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var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
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var pkg = require( './../package.json' ).name;
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var factorial2f = require( './../lib' );
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// MAIN //
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bench( pkg, function benchmark( b ) {
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var x;
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var y;
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var i;
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x = discreteUniform( 100, 0, 56, {
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'dtype': 'int32'
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});
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b.tic();
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for ( i = 0; i < b.iterations; i++ ) {
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y = factorial2f( x[ i%x.length ] );
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if ( isnanf( y ) ) {
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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 ( isnanf( y ) ) {
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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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});

‎lib/node_modules/@stdlib/math/base/special/factorial2f/benchmark/benchmark.native.js

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/**
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* @license Apache-2.0
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*
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* Copyright (c) 2025 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 resolve = require( 'path' ).resolve;
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var bench = require( '@stdlib/bench' );
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var isnanf = require( '@stdlib/math/base/assert/is-nanf' );
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var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
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var tryRequire = require( '@stdlib/utils/try-require' );
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var pkg = require( './../package.json' ).name;
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// VARIABLES //
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var factorial2f = tryRequire( resolve( __dirname, './../lib/native.js' ) );
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var opts = {
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'skip': ( factorial2f instanceof Error )
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};
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// MAIN //
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bench( pkg+'::native', opts, function benchmark( b ) {
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var x;
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var y;
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var i;
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x = discreteUniform( 100, 0, 56, {
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'dtype': 'int32'
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});
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b.tic();
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for ( i = 0; i < b.iterations; i++ ) {
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y = factorial2f( x[ i%x.length ] );
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if ( isnanf( y ) ) {
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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 ( isnanf( y ) ) {
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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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