feat: add C implementation for stats/base/dists/triangular/variance

PR-URL: #4000
Closes: #3824

Co-authored-by: Philipp Burckhardt <pburckhardt@outlook.com>
Co-authored-by: stdlib-bot <noreply@stdlib.io>
Reviewed-by: Philipp Burckhardt <pburckhardt@outlook.com>
Signed-off-by: Philipp Burckhardt <pburckhardt@outlook.com>

Author: 3 people

lib/node_modules/@stdlib/stats/base/dists/triangular/variance/README.md

@@ -59,7 +59,7 @@ var variance = require( '@stdlib/stats/base/dists/triangular/variance' );
 
 #### variance( a, b, c )
 
-Returns the [variance][variance] of a [triangular][triangular-distribution] distribution with minimum support `a`, maximum support`b`, and mode `c`.
+Returns the [variance][variance] of a [triangular][triangular-distribution] distribution with minimum support `a`, maximum support `b`, and mode `c`.
 
 ```javascript
 var v = variance( 0.0, 1.0, 0.8 );
@@ -141,6 +141,104 @@ for ( i = 0; i < 10; i++ ) {
 
 <!-- /.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/triangular/variance.h"
+```
+
+#### stdlib_base_dists_triangular_variance( a, b, c )
+
+Returns the [variance][variance] of a [triangular][triangular-distribution] distribution with minimum support `a`, maximum support `b`, and mode `c`.
+
+```c
+double out = stdlib_base_dists_triangular_variance( 0.0, 1.0, 0.5 );
+// returns ~0.056
+```
+
+The function accepts the following arguments:
+
+-   **a**: `[in] double` minimum support.
+-   **b**: `[in] double` maximum support.
+-   **c**: `[in] double` mode.
+
+```c
+double stdlib_base_dists_triangular_variance( const double a, const double b, const double c );
+```
+
+</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/triangular/variance.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 a;
+    double b;
+    double c;
+    double y;
+    int i;
+
+    for ( i = 0; i < 25; i++ ) {
+        a = random_uniform( 0.0, 10.0 );
+        b = random_uniform( 0.0, 10.0 ) + a;
+        c = a + (b - a) * random_uniform( 0.0, 1.0 );
+        y = stdlib_base_dists_triangular_variance( a, b, c );
+        printf( "a: %lf, b: %lf, c: %lf, Var(X;a,b,c): %lf\n", a, b, c, 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">

lib/node_modules/@stdlib/stats/base/dists/triangular/variance/benchmark/benchmark.js

@@ -21,9 +21,9 @@
 // MODULES //
 
 var bench = require( '@stdlib/bench' );
+var Float64Array = require( '@stdlib/array/float64' );
 var randu = require( '@stdlib/random/base/randu' );
 var isnan = require( '@stdlib/math/base/assert/is-nan' );
-var EPS = require( '@stdlib/constants/float64/eps' );
 var pkg = require( './../package.json' ).name;
 var variance = require( './../lib' );
 
@@ -34,15 +34,23 @@ bench( pkg, function benchmark( b ) {
 	var mode;
 	var min;
 	var max;
+	var len;
 	var y;
 	var i;
 
+	len = 100;
+	min = new Float64Array( len );
+	max = new Float64Array( len );
+	mode = new Float64Array( len );
+	for ( i = 0; i < len; i++ ) {
+		min[ i ] = ( randu() * 10.0 );
+		max[ i ] = ( randu() * 10.0 ) + min[ i ];
+		mode[ i ] = min[ i ] + ( randu() * ( max[ i ] - min[ i ] ) );
+	}
+
 	b.tic();
 	for ( i = 0; i < b.iterations; i++ ) {
-		min = ( randu()*10.0 );
-		max = ( randu()*10.0 ) + min + EPS;
-		mode = ( ( max - min ) * randu() ) + min;
-		y = variance( min, max, mode );
+		y = variance( min[ i % len ], max[ i % len ], mode[ i % len ] );
 		if ( isnan( y ) ) {
 			b.fail( 'should not return NaN' );
 		}

lib/node_modules/@stdlib/stats/base/dists/triangular/variance/benchmark/benchmark.native.js

@@ -0,0 +1,64 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2025 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 randu = require( '@stdlib/random/base/randu' );
+var isnan = require( '@stdlib/math/base/assert/is-nan' );
+var pkg = require( './../package.json' ).name;
+var variance = require( './../lib' );
+
+
+// MAIN //
+
+bench( pkg+'::native', function benchmark( b ) {
+	var mode;
+	var min;
+	var max;
+	var len;
+	var y;
+	var i;
+
+	len = 100;
+	min = new Float64Array( len );
+	max = new Float64Array( len );
+	mode = new Float64Array( len );
+	for ( i = 0; i < len; i++ ) {
+		min[ i ] = ( randu() * 10.0 );
+		max[ i ] = ( randu() * 10.0 ) + min[ i ];
+		mode[ i ] = min[ i ] + ( randu() * ( max[ i ] - min[ i ] ) );
+	}
+
+	b.tic();
+	for ( i = 0; i < b.iterations; i++ ) {
+		y = variance( min[ i % len ], max[ i % len ], mode[ 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();
+});

lib/node_modules/@stdlib/stats/base/dists/triangular/variance/benchmark/c/Makefile

@@ -0,0 +1,146 @@
+#/
+# @license Apache-2.0
+#
+# Copyright (c) 2025 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 := @
+else
+	QUIET :=
+endif
+
+# Determine the OS ([1][1], [2][2]).
+#
+# [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
+else
+ifneq (, $(findstring Windows_NT,$(OS)))
+	OS := WINNT
+endif
+endif
+endif
+endif
+
+# Define the program used for compiling C source files:
+ifdef C_COMPILER
+	CC := $(C_COMPILER)
+else
+	CC := gcc
+endif
+
+# Define the command-line options when compiling C files:
+CFLAGS ?= \
+	-std=c99 \
+	-O3 \
+	-Wall \
+	-pedantic
+
+# Determine whether to generate position independent code ([1][1], [2][2]).
+#
+# [1]: https://gcc.gnu.org/onlinedocs/gcc/Code-Gen-Options.html#Code-Gen-Options
+# [2]: http://stackoverflow.com/questions/5311515/gcc-fpic-option
+ifeq ($(OS), WINNT)
+	fPIC ?=
+else
+	fPIC ?= -fPIC
+endif
+
+# List of includes (e.g., `-I /foo/bar -I /beep/boop/include`):
+INCLUDE ?=
+
+# List of source files:
+SOURCE_FILES ?=
+
+# List of libraries (e.g., `-lopenblas -lpthread`):
+LIBRARIES ?=
+
+# List of library paths (e.g., `-L /foo/bar -L /beep/boop`):
+LIBPATH ?=
+
+# List of C targets:
+c_targets := benchmark.out
+
+
+# RULES #
+
+#/
+# Compiles source files.
+#
+# @param {string} [C_COMPILER] - C compiler (e.g., `gcc`)
+# @param {string} [CFLAGS] - C compiler options
+# @param {(string|void)} [fPIC] - compiler flag determining whether to generate position independent code (e.g., `-fPIC`)
+# @param {string} [INCLUDE] - list of includes (e.g., `-I /foo/bar -I /beep/boop/include`)
+# @param {string} [SOURCE_FILES] - list of source files
+# @param {string} [LIBPATH] - list of library paths (e.g., `-L /foo/bar -L /beep/boop`)
+# @param {string} [LIBRARIES] - list of libraries (e.g., `-lopenblas -lpthread`)
+#
+# @example
+# make
+#
+# @example
+# make all
+#/
+all: $(c_targets)
+
+.PHONY: all
+
+#/
+# Compiles C source files.
+#
+# @private
+# @param {string} CC - C compiler (e.g., `gcc`)
+# @param {string} CFLAGS - C compiler options
+# @param {(string|void)} fPIC - compiler flag determining whether to generate position independent code (e.g., `-fPIC`)
+# @param {string} INCLUDE - list of includes (e.g., `-I /foo/bar`)
+# @param {string} SOURCE_FILES - list of source files
+# @param {string} LIBPATH - list of library paths (e.g., `-L /foo/bar`)
+# @param {string} LIBRARIES - list of libraries (e.g., `-lopenblas`)
+#/
+$(c_targets): %.out: %.c
+	$(QUIET) $(CC) $(CFLAGS) $(fPIC) $(INCLUDE) -o $@ $(SOURCE_FILES) $< $(LIBPATH) -lm $(LIBRARIES)
+
+#/
+# Runs compiled benchmarks.
+#
+# @example
+# make run
+#/
+run: $(c_targets)
+	$(QUIET) ./$<
+
+.PHONY: run
+
+#/
+# Removes generated files.
+#
+# @example
+# make clean
+#/
+clean:
+	$(QUIET) -rm -f *.o *.out
+
+.PHONY: clean