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Date: Wed, 28 Aug 2024 23:32:03 +0300 (MSK)
From: Alexander Monakov <amonakov@ispras.ru>
To: musl@lists.openwall.com
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Subject: Re: [musl] [PATCH] configure: prevent compilers from turning a * b
 + c into fma(a, b, c)


On Wed, 28 Aug 2024, Rich Felker wrote:

> With that said, I don't see how the compiler could ever generate calls
> to fma(), since we're -ffreestanding, but I think it could generate
> inline fma instructions on targets where they're available, and this
> is generally undesirable (see above). For gcc, I think -std=c99
> already has that covered, but I'm not sure what clang does.

Modern Clang implements the FP_CONTRACT pragma, with default state "on".
Of course, the -ffp-contract= command-line switch is also available.

Alexander