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From: Adam Sampson <ats@offog.org>
To: Noah Goldstein via Libc-alpha <libc-alpha@sourceware.org>
Subject: Re: [PATCH v1 2/2] x86_64: Add {u}int_fast defs ideal for x86_64
References: <20220411010913.1061799-1-goldstein.w.n@gmail.com>
 <20220411010913.1061799-2-goldstein.w.n@gmail.com>
Date: Mon, 11 Apr 2022 03:15:25 +0100
In-Reply-To: <20220411010913.1061799-2-goldstein.w.n@gmail.com> (Noah
 Goldstein via Libc-alpha's message of "Sun, 10 Apr 2022 20:09:13
 -0500")
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Noah Goldstein via Libc-alpha <libc-alpha@sourceware.org> writes:

> {u}int_fast{16|32} should never use 64-bit types. 64-bit instructions
> often use more code size (REX prefix) and a variety of instructions
> are slower on many implementations (div, bswap, etc...).

Isn't that going to cause ABI breakage in other libraries, though?
For example, the jasper JPEG2000 decoder library uses stdint.h's
uint_fast32_t in its public API, and the HDF5 scientific data library
includes constants for the sizes of various types including *int*fast*.

Thanks,

-- 
Adam Sampson <ats@offog.org>                         <http://offog.org/>