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feat: add math/base/special/factorial2
Closes: #44 PR-URL: #1112 Co-authored-by: Athan Reines <kgryte@gmail.com> Reviewed-by: Athan Reines <kgryte@gmail.com>
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‎lib/node_modules/@stdlib/math/base/special/factorial2/README.md

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<!--
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@license Apache-2.0
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Copyright (c) 2023 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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# factorial2
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> [Double factorial][double-factorial] function.
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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 factorial2 = require( '@stdlib/math/base/special/factorial2' );
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```
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#### factorial2( n )
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Evaluates the [double factorial][double-factorial] of `n`.
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```javascript
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var v = factorial2( 2 );
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// returns 2
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v = factorial2( 3 );
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// returns 3
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v = factorial2( 0 );
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// returns 1
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v = factorial2( 4 );
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// returns 8
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v = factorial2( 5 );
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// returns 15
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v = factorial2( NaN );
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// returns NaN
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v = factorial2( 301 );
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// returns Infinity
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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 oneTo = require( '@stdlib/array/base/one-to' );
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var factorial2 = require( '@stdlib/math/base/special/factorial2' );
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var values = oneTo( 300 );
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var i;
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for ( i = 0; i < values.length; i++ ) {
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console.log( 'f(%d): %d', values[ i ], factorial2( values[ i ] ) );
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}
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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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[double-factorial]: https://en.wikipedia.org/wiki/Double_factorial
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</section>
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<!-- /.links -->

‎lib/node_modules/@stdlib/math/base/special/factorial2/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) 2023 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 pkg = require( './../package.json' ).name;
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var factorial2 = require( './../lib' );
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// MAIN //
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bench( pkg, function benchmark( b ) {
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var y;
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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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y = factorial2( i%301 );
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if ( isnan( 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 ( isnan( 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/factorial2/benchmark/cpp/boost/Makefile

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

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