feat: add math/base/special/factorial2

Closes: #44
PR-URL: 	#1112
Co-authored-by: Athan Reines <[email protected]>
Reviewed-by: Athan Reines <[email protected]>

lib/node_modules/@stdlib/math/base/special/factorial2/README.md

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+<!--
+
+@license Apache-2.0
+
+Copyright (c) 2023 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.
+
+-->
+
+# factorial2
+
+> [Double factorial][double-factorial] function.
+
+<section class="intro">
+
+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`.
+
+Thus, for example, `5!!` is `5 * 3 * 1 = 15` and `8!!` is `8 * 6 * 4 * 2 = 384`.
+
+</section>
+
+<!-- /.intro -->
+
+<section class="usage">
+
+## Usage
+
+```javascript
+var factorial2 = require( '@stdlib/math/base/special/factorial2' );
+```
+
+#### factorial2( n )
+
+Evaluates the [double factorial][double-factorial] of `n`.
+
+```javascript
+var v = factorial2( 2 );
+// returns 2
+
+v = factorial2( 3 );
+// returns 3
+
+v = factorial2( 0 );
+// returns 1
+
+v = factorial2( 4 );
+// returns 8
+
+v = factorial2( 5 );
+// returns 15
+
+v = factorial2( NaN );
+// returns NaN
+
+v = factorial2( 301 );
+// returns Infinity
+```
+
+</section>
+
+<!-- /.usage -->
+
+<section class="examples">
+
+## Examples
+
+<!-- eslint no-undef: "error" -->
+
+```javascript
+var oneTo = require( '@stdlib/array/base/one-to' );
+var factorial2 = require( '@stdlib/math/base/special/factorial2' );
+
+var values = oneTo( 300 );
+
+var i;
+for ( i = 0; i < values.length; i++ ) {
+    console.log( 'f(%d): %d', values[ i ], factorial2( values[ i ] ) );
+}
+```
+
+</section>
+
+<!-- /.examples -->
+
+<!-- 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">
+
+[double-factorial]: https://en.wikipedia.org/wiki/Double_factorial
+
+</section>
+
+<!-- /.links -->

lib/node_modules/@stdlib/math/base/special/factorial2/benchmark/benchmark.js

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+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2023 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 isnan = require( '@stdlib/math/base/assert/is-nan' );
+var pkg = require( './../package.json' ).name;
+var factorial2 = require( './../lib' );
+
+
+// MAIN //
+
+bench( pkg, function benchmark( b ) {
+	var y;
+	var i;
+
+	b.tic();
+	for ( i = 0; i < b.iterations; i++ ) {
+		y = factorial2( i%301 );
+		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();
+});

lib/node_modules/@stdlib/math/base/special/factorial2/benchmark/cpp/boost/Makefile

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+#/
+# @license Apache-2.0
+#
+# Copyright (c) 2023 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.
+#/
+
+
+# VARIABLES #
+
+ifndef VERBOSE
+	QUIET := @
+endif
+
+# Specify the path to Boost:
+BOOST ?=
+
+# Determine the OS:
+#
+# [1]: https://en.wikipedia.org/wiki/Uname#Examples
+# [2]: http://stackoverflow.com/a/27776822/2225624
+OS ?= $(shell uname)
+ifneq (, $(findstring MINGW,$(OS)))
+	OS := WINNT
+else
+ifneq (, $(findstring MSYS,$(OS)))
+	OS := WINNT
+else
+ifneq (, $(findstring CYGWIN,$(OS)))
+	OS := WINNT
+endif
+endif
+endif
+
+# Define the program used for compiling C++ source files:
+ifdef CXX_COMPILER
+	CXX := $(CXX_COMPILER)
+else
+	CXX := g++
+endif
+
+# Define the command-line options when compiling C++ files:
+CXXFLAGS ?= \
+	-std=c++11 \
+	-O3 \
+	-Wall \
+	-pedantic
+
+# Determine whether to generate [position independent code][1]:
+#
+# [1]: https://gcc.gnu.org/onlinedocs/gcc/Code-Gen-Options.html#Code-Gen-Options
+# [2]: http://stackoverflow.com/questions/5311515/gcc-fpic-option
+ifeq ($(OS), WINNT)
+	fPIC ?=
+else
+	fPIC ?= -fPIC
+endif
+
+# List of C++ targets:
+cxx_targets := benchmark.out
+
+
+# TARGETS #
+
+# Default target.
+#
+# This target is the default target.
+
+all: $(cxx_targets)
+
+.PHONY: all
+
+
+# Compile C++ source.
+#
+# This target compiles C++ source files.
+
+$(cxx_targets): %.out: %.cpp $(BOOST)
+	$(QUIET) $(CXX) $(CXXFLAGS) $(fPIC) -I $(BOOST) -o $@ $< -lm
+
+
+# Run a benchmark.
+#
+# This target runs a benchmark.
+
+run: $(cxx_targets)
+	$(QUIET) ./$<
+
+.PHONY: run
+
+
+# Perform clean-up.
+#
+# This target removes generated files.
+
+clean:
+	$(QUIET) -rm -f *.o *.out
+
+.PHONY: clean