JuliaLang/julia

IEEE-754 recommended functions

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#6,148 opened on Mar 13, 2014

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Description

As I was enjoying the entertaining read that is the IEEE-754 standard for floating point arithmetic, I noticed they recommend some functions (section 9.2), of which we currently lack:

  • exp2m1: 2^x-1
  • exp10m1: 10^x-1
  • log2p1: log2(1+x) (might want to call this log21p, to match log1p?)
  • log10p1: log10(1+x) (similarly, log101p?)
  • rsqrt: 1/sqrt(x)
  • compound: (1+x)^n (pow1p?)
  • rootn: x^(1/n)
  • various inverse trig-pi functions, e.g. atanpi: atan(x)/pi (somewhat confusingly, not all of these are mentioned in the table, although they are referred to in the text below).

There's also three different "pow" functions: pown for integer exponents, two for handling floating-point exponents pow and powr which seem to differ mostly in how signals are raised, so we could probably wait until #2976 is completed.

Contributor guide

Tech stack
None
Domain
backend
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.
1-2 days
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.
mostly clear
Prerequisites
Basic understanding of IEEE 754Familiarity with Julia's Base math module
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30
Research direction
The issue requests implementing several IEEE 754 recommended functions (exp2m1, exp10m1, log2p1, log10p1, rsqrt, compound, rootn, and inverse trig pi functions). The discussion in the comments touches on naming conventions (e.g., log21p vs log2p1). Prerequisite understanding of existing similar functions like log1p and expm1 in Julia's Base math module. No pull requests or maintainer responses are visible yet. The implementation would involve adding new methods in Julia's Base and possibly C or LLVM intrinsics.