JuliaLang/julia

Proposal: expose flags set by floating-point exceptions

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#2,976 opened on Apr 30, 2013

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Description

There is currently no Base function that allows users to check for the flags set by floating-point operations.1 This does not allow the user to compute in a fully IEEE-compatible manner and could decrease code legibility should the user be forced to test implicitly for a raised flag by inspecting the consequences of the computation.

This continues a discussion started in #2085, and extends the concept of overflow checking proposed for integers in #855.

  • Detect the five flags raised by floating-point exceptions
    • Invalid
    • Division by zero
    • Overflow
    • Underflow
    • Inexact
  • Allow the floating-point rounding mode to be set:
    • round to nearest, ties round to the nearest even digit in the required position
    • round to nearest, ties round away from zero
    • round up toward Inf
    • round down toward -Inf
    • round toward 0
  • [ ] Honor the difference between quiet and signaling NaNs
  • Expose similar flag-handling behavior from MPFR

cc: @andrioni @JeffBezanson

Contributor guide

Tech stack
None
Domain
performance
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
over 1 week
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
IEEE floating pointJulia base libraryC programming
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
15
Research direction
Investigate the existing floating point exception handling in Julia's runtime, focusing on the `Base` module. Refer to previous discussions in issues #2085 and #855. Look at how the rounding mode is already implemented and extend similar mechanisms to detect flags. Consider using MPFR library for flag handling. Examine comments from @andrioni and @JeffBezanson for guidance.