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From: "harald at gigawatt dot nl" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/114363] inconsistent optimization of pow(x,2)+pow(y,2)
Date: Sat, 16 Mar 2024 10:37:24 +0000	[thread overview]
Message-ID: <bug-114363-4-IbrhylVCEu@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-114363-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114363

Harald van Dijk <harald at gigawatt dot nl> changed:

           What    |Removed                     |Added
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                 CC|                            |harald at gigawatt dot nl

--- Comment #1 from Harald van Dijk <harald at gigawatt dot nl> ---
This is, I believe, correct. Before C++11, calling std::pow with float and int
arguments, it returned a float. As of C++11, it returns a double.

If the result of pow(x,2) is immediately converted to float, then it is a valid
optimisation to convert it to x*x: that is guaranteed to produce the exact same
result. But if it isn't, then converting to x*x loses accuracy and alters the
result.

You can call std::powf instead of std::pow to avoid the promotion to double.

  reply	other threads:[~2024-03-16 10:37 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-03-16  9:31 [Bug tree-optimization/114363] New: " vincenzo.innocente at cern dot ch
2024-03-16 10:37 ` harald at gigawatt dot nl [this message]
2024-03-16 11:26 ` [Bug tree-optimization/114363] " xry111 at gcc dot gnu.org
2024-03-16 12:58 ` jakub at gcc dot gnu.org
2024-03-16 15:06 ` vincenzo.innocente at cern dot ch

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