Bug 20508 – std.math.pow(-infinity, y) does not return NaN for imaginary or complex results

void main() { import std.stdio, std.math; writefln("%s", pow(-double.infinity, 0.5)); // wrongly prints "inf" writefln("%s", sqrt(-double.infinity)); // correctly prints "-nan" } I realize that pow() is following the spec given in the documentation here, and that at least some implementations of the C standard library apparently do the same thing. But, the behaviour of pow() is mathematically incorrect here, and sabotages the ability of floating-point algorithms to detect and handle the generation of imaginary and complex results properly. Is there an actual good reason it works this way, or was this just copied from some broken C implementation?

IMHO the current implementation is broken. Probably it's been implemented with integers in mind (for the exponent). Before fixing this, I'd like to completely understand -inf ^^ y for any y. I will be able to figure this out myself, but this will take a while. So if you've got a link to a page, where this is explained or could provide this information, it would be great. :-)

@berni44 created dlang/phobos pull request #7363 "Fix Issue 20508 - std.math.pow(-infinity, y) does not return NaN for imaginary or complex results" fixing this issue: - Fix Issue 20508 - std.math.pow(-infinity, y) does not return NaN for imaginary or complex results https://github.com/dlang/phobos/pull/7363

@berni44 created dlang/phobos pull request #7747 "Fix Issue 20508 - std.math.pow(-infinity, y) does not return NaN for imaginary or complex results" fixing this issue: - Fix Issue 20508 - std.math.pow(-infinity, y) does not return NaN for imaginary or complex results https://github.com/dlang/phobos/pull/7747

dlang/phobos pull request #7747 "Fix Issue 20508 - std.math.pow(-infinity, y) does not return NaN for imaginary or complex results" was merged into master: - 7cc7d4d01a6f80aaaa1ada095f553c151f0f49bc by Bernhard Seckinger: Fix Issue 20508 - std.math.pow(-infinity, y) does not return NaN for imaginary or complex results https://github.com/dlang/phobos/pull/7747