From: ngotogenome@...
Date: 2015-10-13T03:12:46+00:00
Subject: [ruby-core:71068] [Ruby trunk - Bug #11582] On Solaris, Rational#** returns -Infinity for Rational(0) when passed a negative Float

Issue #11582 has been updated by Naohisa Goto.



> Does 0.0 ** -1 return -Infinity too?

Yes, with default compiler option.
On Solaris, the 0.0 ** -1 could return 3 different values depending on compile-time options: 0, -Infinity, +Infinity.

See below for list of corner-case variations of numerical calculations.
http://docs.oracle.com/cd/E37069_01/html/E39019/z4000ac610479.html

> It isn't a problem?

I don't know.

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Bug #11582: On Solaris, Rational#** returns -Infinity for Rational(0) when passed a negative Float
https://bugs.ruby-lang.org/issues/11582#change-54436

* Author: Benoit Daloze
* Status: Open
* Priority: Normal
* Assignee: 
* ruby -v: 
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN
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For instance,

> Rational(0, 1) ** -1.0
=> +Infinity on most platforms, -Infinity on Solaris by default.

The Rational is implicitly converted to the Float value 0.0, and the libm function pow(0.0, -1.0) is called.

Should this kind of behavior be made consistent by Ruby or should we accept this as dependent on the libm/libc used?

They are likely other edges cases for pow() which might differ, and I think in general
Ruby should try to unify these cases so the behavior is consistent across platforms at least for arithmetic.

For more details, please see https://github.com/ruby/rubyspec/issues/134 reported by ngoto.



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