feat: add implementation for stats/base/dists/halfnormal/quantile

lib/node_modules/@stdlib/stats/base/dists/halfnormal/quantile/README.md

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+<!--
+
+@license Apache-2.0
+
+Copyright (c) 2026 The Stdlib Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+   http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+
+-->
+
+# Quantile Function
+
+> [Half-normal][halfnormal-distribution] distribution [quantile function][quantile-function].
+
+<section class="intro">
+
+The [quantile function][quantile-function] for a [Half-normal][halfnormal-distribution] random variable is
+
+<!-- <equation class="equation" label="eq:halfnormal_quantile_function" align="center" raw="Q(p;\sigma) = \sigma\sqrt{2}\,\operatorname{erf}^{-1}(p)" alt="Quantile function for a Half-normal distribution."> -->
+
+```math
+Q(p;\sigma) = \sigma\sqrt{2}\,\mathop{\mathrm{erf}}^{-1}(p)
+```
+
+<!-- <div class="equation" align="center" data-raw-text="Q(p;\sigma) = \sigma\sqrt{2}\,\operatorname{erf}^{-1}(p)" data-equation="eq:halfnormal_quantile_function">
+    <img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@bb29798d6de5a1de3c633e038f832c3c04207865/lib/node_modules/@stdlib/stats/base/dists/halfnormal/quantile/docs/img/equation_halfnormal_quantile_function.svg" alt="Quantile function for a Half-normal distribution.">
+    <br>
+</div> -->
+
+<!-- </equation> -->
+
+for `0 <= p < 1`, where `σ > 0` is the scale parameter.
+
+</section>
+
+<!-- /.intro -->
+
+<section class="usage">
+
+## Usage
+
+```javascript
+var quantile = require( '@stdlib/stats/base/dists/halfnormal/quantile' );
+```
+
+#### quantile( p, sigma )
+
+Evaluates the [quantile function][quantile-function] for a [Half-normal][halfnormal-distribution] distribution with scale parameter `sigma`.
+
+```javascript
+var y = quantile( 0.5, 1.0 );
+// returns ~0.674
+
+y = quantile( 0.8, 2.0 );
+// returns ~2.563
+```
+
+If provided a probability `p` outside the interval `[0,1]`, the function returns `NaN`.
+
+```javascript
+var y = quantile( 1.9, 1.0 );
+// returns NaN
+
+y = quantile( -0.1, 1.0 );
+// returns NaN
+```
+
+If provided `NaN` as any argument, the function returns `NaN`.
+
+```javascript
+var y = quantile( NaN, 1.0 );
+// returns NaN
+
+y = quantile( 0.0, NaN );
+// returns NaN
+```
+
+If provided `sigma < 0`, the function returns `NaN`.
+
+```javascript
+var y = quantile( 0.4, -1.0 );
+// returns NaN
+```
+
+If provided `sigma = 0`, the function evaluates the [quantile function][quantile-function] of a [degenerate distribution][degenerate-distribution] centered at `0`.
+
+```javascript
+var y = quantile( 0.3, 0.0 );
+// returns 0.0
+
+y = quantile( 0.9, 0.0 );
+// returns 0.0
+```
+
+#### quantile.factory( sigma )
+
+Returns a function for evaluating the [quantile function][quantile-function] of a [Half-normal][halfnormal-distribution] distribution with parameter `sigma`.
+
+```javascript
+var myquantile = quantile.factory( 4.0 );
+
+var y = myquantile( 0.2 );
+// returns ~1.013
+
+y = myquantile( 0.8 );
+// returns ~5.126
+```
+
+</section>
+
+<!-- /.usage -->
+
+<section class="examples">
+
+## Examples
+
+<!-- eslint no-undef: "error" -->
+
+```javascript
+var uniform = require( '@stdlib/random/array/uniform' );
+var logEachMap = require( '@stdlib/console/log-each-map' );
+var quantile = require( '@stdlib/stats/base/dists/halfnormal/quantile' );
+
+var opts = {
+    'dtype': 'float64'
+};
+var sigma = uniform( 10, 0.0, 20.0, opts );
+var p = uniform( 10, 0.0, 1.0, opts );
+
+logEachMap( 'p: %lf, σ: %lf, Q(p;σ): %lf', p, sigma, quantile );
+```
+
+</section>
+
+<!-- /.examples -->
+
+<!-- C interface documentation. -->
+
+* * *
+
+<section class="c">
+
+## C APIs
+
+<!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. -->
+
+<section class="intro">
+
+</section>
+
+<!-- /.intro -->
+
+<!-- C usage documentation. -->
+
+<section class="usage">
+
+### Usage
+
+```c
+#include "stdlib/stats/base/dists/halfnormal/quantile.h"
+```
+
+#### stdlib_base_dists_halfnormal_quantile( p, sigma )
+
+Evaluates the [quantile function][quantile-function] for a [Half-normal][halfnormal-distribution] distribution with parameter `sigma` (scale).
+
+```c
+double y = stdlib_base_dists_halfnormal_quantile( 0.8, 1.0 );
+// returns ~1.282
+```
+
+The function accepts the following arguments:
+
+-   **p**: `[in] double` probability.
+-   **sigma**: `[in] double` scale parameter.
+
+```c
+double stdlib_base_dists_halfnormal_quantile( const double p, const double sigma );
+```
+
+</section>
+
+<!-- /.usage -->
+
+<!-- C API usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
+
+<section class="notes">
+
+</section>
+
+<!-- /.notes -->
+
+<!-- C API usage examples. -->
+
+<section class="examples">
+
+### Examples
+
+```c
+#include "stdlib/stats/base/dists/halfnormal/quantile.h"
+#include "stdlib/constants/float64/eps.h"
+#include <stdlib.h>
+#include <stdio.h>
+
+static double random_uniform( const double min, const double max ) {
+    double v = (double)rand() / ( (double)RAND_MAX + 1.0 );
+    return min + ( v*(max-min) );
+}
+
+int main( void ) {
+    double sigma;
+    double p;
+    double y;
+    int i;
+
+    for ( i = 0; i < 10; i++ ) {
+        p = random_uniform( 0.0, 1.0 );
+        sigma = random_uniform( STDLIB_CONSTANT_FLOAT64_EPS, 20.0 );
+        y = stdlib_base_dists_halfnormal_quantile( p, sigma );
+        printf( "p:%lf, σ: %lf, Q(p;σ): %lf\n", p, sigma, y );
+    }
+}
+```
+
+</section>
+
+<!-- /.examples -->
+
+</section>
+
+<!-- /.c -->
+
+<!-- Section to include cited references. If references are included, add a horizontal rule *before* the section. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
+
+<section class="references">
+
+</section>
+
+<!-- /.references -->
+
+<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->
+
+<section class="related">
+
+</section>
+
+<!-- /.related -->
+
+<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
+
+<section class="links">
+
+[quantile-function]: https://en.wikipedia.org/wiki/Quantile_function
+
+[halfnormal-distribution]: https://en.wikipedia.org/wiki/Half-normal_distribution
+
+[degenerate-distribution]: https://en.wikipedia.org/wiki/Degenerate_distribution
+
+</section>
+
+<!-- /.links -->

lib/node_modules/@stdlib/stats/base/dists/halfnormal/quantile/benchmark/benchmark.js

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+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2026 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*    http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+'use strict';
+
+// MODULES //
+
+var bench = require( '@stdlib/bench' );
+var Float64Array = require( '@stdlib/array/float64' );
+var uniform = require( '@stdlib/random/base/uniform' );
+var isnan = require( '@stdlib/math/base/assert/is-nan' );
+var EPS = require( '@stdlib/constants/float64/eps' );
+var pkg = require( './../package.json' ).name;
+var quantile = require( './../lib' );
+
+
+// MAIN //
+
+bench( pkg, function benchmark( b ) {
+	var sigma;
+	var len;
+	var p;
+	var y;
+	var i;
+
+	len = 100;
+	p = new Float64Array( len );
+	sigma = new Float64Array( len );
+	for ( i = 0; i < len; i++ ) {
+		p[ i ] = uniform( 0.0, 1.0 );
+		sigma[ i ] = uniform( EPS, 20.0 );
+	}
+
+	b.tic();
+	for ( i = 0; i < b.iterations; i++ ) {
+		y = quantile( p[ i % len ], sigma[ i % len ] );
+		if ( isnan( y ) ) {
+			b.fail( 'should not return NaN' );
+		}
+	}
+	b.toc();
+	if ( isnan( y ) ) {
+		b.fail( 'should not return NaN' );
+	}
+	b.pass( 'benchmark finished' );
+	b.end();
+});
+
+bench( pkg+':factory', function benchmark( b ) {
+	var myquantile;
+	var sigma;
+	var len;
+	var p;
+	var y;
+	var i;
+
+	sigma = 4.0;
+	myquantile = quantile.factory( sigma );
+	len = 100;
+	p = new Float64Array( len );
+	for ( i = 0; i < len; i++ ) {
+		p[ i ] = uniform( 0.0, 1.0 );
+	}
+
+	b.tic();
+	for ( i = 0; i < b.iterations; i++ ) {
+		y = myquantile( p[ i % len ] );
+		if ( isnan( y ) ) {
+			b.fail( 'should not return NaN' );
+		}
+	}
+	b.toc();
+	if ( isnan( y ) ) {
+		b.fail( 'should not return NaN' );
+	}
+	b.pass( 'benchmark finished' );
+	b.end();
+});