feat: add math/base/special/trunc2f by Aashrith-Vellampalli · Pull Request #10673 · stdlib-js/stdlib

Aashrith-Vellampalli · 2026-03-03T06:47:57Z

Resolves #649.

Description

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This pull request:

This PR adds C and JavaScript implementations of math/base/special/trunc2f, including tests and benchmarks.

Related Issues

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This pull request has the following related issues:

[RFC]: Add C implementations to base special math functions (tracking issue) #649

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Read, understood, and followed the contributing guidelines.

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stdlib-bot · 2026-03-03T06:48:09Z

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stdlib-bot · 2026-03-03T12:04:31Z

⚠️ Tracking Issue Closure Warning ⚠️

I noticed your PR description contains closing keywords ("Resolves", "Closes", or "Fixes") referencing a "Tracking Issue".

Why this matters:
Tracking issues should typically remain open until all related sub-issues are completed. GitHub automatically closes issues with such closing keywords when the PR is merged. For more information, see GitHub's documentation on using keywords in issues and pull requests.

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Use "Progresses" instead to reference the tracking issue without automatically closing it.

Thank you for your contribution to the project!

Planeshifter

Thanks for opening a PR!

Left a bunch of comments; overall, the PR will require significant clean-up, mainly ensuring to use single-precision variants of all dependencies.

Planeshifter · 2026-03-03T17:38:05Z

lib/node_modules/@stdlib/math/base/special/trunc2f/README.md

+
+-->
+
+# trunc2


H1 should be trunc2f, not trunc2.

Suggested change

# trunc2

# trunc2f

Planeshifter · 2026-03-03T17:38:09Z

lib/node_modules/@stdlib/math/base/special/trunc2f/README.md

+double y = stdlib_base_trunc2f( -4.2 );
+// returns -4.0


This is a single-precision (float) function. The C usage example should use float, not double, and the literal should have the f suffix. See floor2f for reference.

Suggested change

double y = stdlib_base_trunc2f( -4.2 );

// returns -4.0

float y = stdlib_base_trunc2f( -4.2f );

// returns -4.0f

Planeshifter · 2026-03-03T17:38:13Z

lib/node_modules/@stdlib/math/base/special/trunc2f/README.md

+int main( void ) {
+    const double x[] = { 3.14, -3.14, 0.0, 0.0 / 0.0 };
+
+    double y;
+    int i;
+    for ( i = 0; i < 4; i++ ) {
+        y = stdlib_base_trunc2f( x[ i ] );
+        printf( "trunc2f(%lf) = %lf\n", x[ i ], y );
+    }
+}


The C example section uses double throughout but this is a float function. Array should be const float x[] with f-suffixed literals, y should be float, and printf should use %f not %lf. Compare with floor2f.

Suggested change

int main( void ) {

const double x[] = { 3.14, -3.14, 0.0, 0.0 / 0.0 };

double y;

int i;

for ( i = 0; i < 4; i++ ) {

y = stdlib_base_trunc2f( x[ i ] );

printf( "trunc2f(%lf) = %lf\n", x[ i ], y );

}

}

int main( void ) {

const float x[] = { 3.14f, -3.14f, 0.0f, 0.0f / 0.0f };

float y;

int i;

for ( i = 0; i < 4; i++ ) {

y = stdlib_base_trunc2f( x[ i ] );

printf( "trunc2f(%f) = %f\n", x[ i ], y );

}

}

Planeshifter · 2026-03-03T17:38:22Z

lib/node_modules/@stdlib/math/base/special/trunc2f/lib/main.js

+var isnan = require( '@stdlib/math/base/assert/is-nan' );
+var isInfinite = require( '@stdlib/math/base/assert/is-infinite' );
+var pow = require( '@stdlib/math/base/special/pow' );
+var floor = require( '@stdlib/math/base/special/floor' );
+var log2 = require( '@stdlib/math/base/special/log2' );
+
+
+// MAIN //
+
+/**
+* Rounds a numeric value to the nearest power of two toward zero.
+*
+* @param {number} x - input value
+* @returns {number} rounded value
+*
+* @example
+* var v = trunc2f( 3.141592653589793 );
+* // returns 2.0
+*
+* @example
+* var v = trunc2f( 13.0 );
+* // returns 8.0
+*
+* @example
+* var v = trunc2f( -0.314 );
+* // returns -0.25
+*/
+function trunc2f( x ) {
+	var sign;
+	if (
+		isnan( x ) ||
+		isInfinite( x ) ||
+		x === 0.0
+	) {
+		return x;
+	}
+	if ( x < 0 ) {
+		x = -x;
+		sign = -1.0;
+	} else {
+		sign = 1.0;
+	}
+	return sign * pow( 2.0, floor( log2( x ) ) );


This is a single-precision function but the implementation operates entirely in double precision. Compare with floor2f/lib/main.js which uses isnanf, isInfinitef, powf, floorf, f32() wrappers, and float32 constants.

At minimum you need:

isnanf / isInfinitef instead of isnan / isInfinite

powf instead of pow

floorf instead of floor

f32() conversions at key points to ensure single-precision semantics

Float32 constants (ZERO, TWO, ONE) like floor2f does

Without these, the function produces double-precision results, which defeats the purpose of the f suffix.

Planeshifter · 2026-03-03T17:38:27Z

lib/node_modules/@stdlib/math/base/special/trunc2f/src/main.c

+	if ( stdlib_base_is_nan( x ) || stdlib_base_is_infinite( x ) || x == 0.0f ) {
+		return x;
+	}
+
+	if ( x < 0.0f ) {
+		sign = -1.0f;
+	} else {
+		sign = 1.0f;
+	}
+	ax = stdlib_base_absf( x );
+	stdlib_base_frexpf( x,&frac ,&exp );
+
+	return sign * stdlib_base_ldexpf( 1.0f, exp-1 );


Two issues here:

stdlib_base_is_nan and stdlib_base_is_infinite are double-precision checks. For a float function, use stdlib_base_is_nanf and stdlib_base_is_infinitef (from is_nanf.h / is_infinitef.h).

ax is computed but never used -- frexpf is called with x (which can be negative) instead of ax. Either use ax as the argument to frexpf, or remove ax and the absf include entirely since frexpf handles the sign via the exponent anyway.

Also, spacing: &frac ,&exp should be &frac, &exp.

Planeshifter · 2026-03-03T17:39:07Z

lib/node_modules/@stdlib/math/base/special/trunc2f/manifest.json

+      "dependencies": [
+        "@stdlib/math/base/napi/unary",
+        "@stdlib/math/base/special/frexpf",
+        "@stdlib/math/base/special/ldexpf",
+        "@stdlib/math/base/assert/is-nan",
+        "@stdlib/math/base/assert/is-infinite"
+      ]
+    },
+    {
+      "task": "benchmark",
+      "src": [
+        "./src/main.c"
+      ],
+      "include": [
+        "./include"
+      ],
+      "libraries": [
+        "-lm"
+      ],
+      "libpath": [],
+      "dependencies": [
+        "@stdlib/math/base/napi/unary",
+        "@stdlib/math/base/special/frexpf",
+        "@stdlib/math/base/special/ldexpf",
+        "@stdlib/math/base/assert/is-nan",
+        "@stdlib/math/base/assert/is-infinite"
+      ]


The manifest.json dependencies don't match what src/main.c actually uses. Currently listed: frexpf, ldexpf, is-nan, is-infinite. But main.c also includes absf and float32/base/exponent (unused). And is-nan/is-infinite should be is-nanf/is-infinitef once main.c is fixed.

Please reconcile these -- the deps should exactly match what the C code #includes. Also, benchmark and examples tasks should not include @stdlib/math/base/napi/unary (that's only needed for the build task). See floor2f/manifest.json for reference.

Planeshifter · 2026-03-03T17:39:09Z

lib/node_modules/@stdlib/math/base/special/trunc2f/test/test.native.js

+	v = trunc2f( Math.fround(x + Math.fround(x/3.0)) );
+	t.strictEqual( v, expected, 'returns expected value' );
+
+	expected = -SMALLEST_SUBNORMAL


Missing semicolon:

Suggested change

expected = -SMALLEST_SUBNORMAL

expected = -SMALLEST_SUBNORMAL;

Planeshifter · 2026-03-03T17:39:16Z

lib/node_modules/@stdlib/math/base/special/trunc2f/test/test.js

+	t.end();
+});
+
+tape( 'the function returns the minimum double-precision floating-point value if provided the minimum double-precision floating-point value', function test( t ) {


This says "double-precision" but should be "single-precision" since this is a float32 function. Also, the reference package uses isnanf instead of isnan.

Suggested change

tape( 'the function returns the minimum double-precision floating-point value if provided the minimum double-precision floating-point value', function test( t ) {

tape( 'the function returns the minimum single-precision floating-point value if provided the minimum single-precision floating-point value', function test( t ) {

Planeshifter · 2026-03-03T17:39:18Z

lib/node_modules/@stdlib/math/base/special/trunc2f/test/test.native.js

+	t.end();
+});
+
+tape( 'the function returns the minimum double-precision floating-point value if provided the minimum double-precision floating-point value', opts, function test( t ) {


Same as test.js -- "double-precision" should be "single-precision".

Suggested change

tape( 'the function returns the minimum double-precision floating-point value if provided the minimum double-precision floating-point value', opts, function test( t ) {

tape( 'the function returns the minimum single-precision floating-point value if provided the minimum single-precision floating-point value', opts, function test( t ) {

Planeshifter · 2026-03-03T17:39:20Z

lib/node_modules/@stdlib/math/base/special/trunc2f/src/main.c

+#include "stdlib/number/float32/base/exponent.h"
+#include "stdlib/math/base/special/frexpf.h"


float32/base/exponent is included but never used. Remove this unused include.

Suggested change

#include "stdlib/number/float32/base/exponent.h"

#include "stdlib/math/base/special/frexpf.h"

#include "stdlib/math/base/special/frexpf.h"

feat: add trunc2f

7eef4a8

stdlib-bot added the Math Issue or pull request specific to math functionality. label Mar 3, 2026

stdlib-bot added First-time Contributor A pull request from a contributor who has never previously committed to the project repository. Needs Review A pull request which needs code review. labels Mar 3, 2026

stdlib-bot added the Potential Duplicate There might be another pull request resolving the same issue. label Mar 4, 2026

Planeshifter requested changes Mar 4, 2026

View reviewed changes

Planeshifter added Needs Changes Pull request which needs changes before being merged. and removed Needs Review A pull request which needs code review. labels Mar 4, 2026

	expected = -SMALLEST_SUBNORMAL
	expected = -SMALLEST_SUBNORMAL;

	tape( 'the function returns the minimum double-precision floating-point value if provided the minimum double-precision floating-point value', function test( t ) {
	tape( 'the function returns the minimum single-precision floating-point value if provided the minimum single-precision floating-point value', function test( t ) {

		#include "stdlib/number/float32/base/exponent.h"
		#include "stdlib/math/base/special/frexpf.h"


		-->

		# trunc2

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Aashrith-Vellampalli commented Mar 3, 2026

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stdlib-bot commented Mar 3, 2026

Getting Started

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Running Tests Locally

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