From: ray.chason@...
Date: 2021-04-15T01:17:10+00:00
Subject: [ruby-core:103453] [Ruby master Bug#17804] Math.cbrt(0.0) returns	NaN

Issue #17804 has been reported by chasonr (Ray chason).

----------------------------------------
Bug #17804: Math.cbrt(0.0) returns NaN
https://bugs.ruby-lang.org/issues/17804

* Author: chasonr (Ray chason)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.0.1p64 (2021-04-05 revision 0fb782ee38) [x86_64-linux]
* Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN
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Math.cbrt(0.0) returns NaN. It should return 0.0.

From reading the implementation, I expect this bug to happen only if glibc is in use. The failing section reads:

#if defined __GLIBC__
    if (isfinite(r)) {
	r = (2.0 * r + (f / r / r)) / 3.0;
    }
#endif

and this produces a NaN when f and r are both 0.



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