llvm/llvm-project

[libc][math] Add missing isnan variants for float16, bfloat16, and float128

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#195,400 opened on May 2, 2026

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good first issuelibc

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Description

The current implementations of isnan are limited to float, double, and long double. We should add support for the remaining types (float16, bfloat16, and float128).

Additionally, the existing implementations currently rely on __builtin_isnan. I think refactoring them to use fputil would be better, especially since issignaling already uses fputil.

Contributor guide

Research direction
Study existing isnan implementations for float, double, long double in llvm project/libc. Understand fputil library. Add implementations for float16, bfloat16, float128 using appropriate builtins or fputil. Run math tests.
Tech stack
ccpp
Domain
api
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
CC++Git
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40