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Date: Wed, 6 Jan 2016 10:39:34 +1100
From: Matthew Fernandez <>
To: <>
Subject: Re: string word-at-a-time and atomic.h FAQ on twitter

On 06/01/16 04:50, Rich Felker wrote:
> On Tue, Jan 05, 2016 at 05:46:41PM +0100, Szabolcs Nagy wrote:
>> ...  however i find lto a
>> weak excuse to rewrite strlen in asm for all targets since lto
>> of libc is still not practical ...

This is an interesting comment; would you mind expanding on this a little? Though we don't do it
regularly, we have used LTO on Musl C in the past. I am not aware of any Musl-specific issues we
encountered, though it's entirely possible our build contained latent bugs.

>> 2) musl atomic.h sync primitives
>> the primitives in atomic.h are carefully designed for musl's
>> pthread implementation (which seems to me far ahead of other
>> implementations in terms of correctness and portability).
>> however they are not documented in the code (only in the git
>> log) so ppl assume they understand their precise interface
>> contract by guessing (which is usually wrong because the names
>> are misleading).
>> musl does not use 64-bit atomic primitives, a_and_64 and a_or_64
>> have secific uses in the malloc implementation which determine
>> their semantics.
> I think we could replace them with atomic bitset/bitclear. They're
> only used in a couple places, mainly malloc.

This would certainly make us happier. We've been bitten a couple of times by newcomers (and myself
once) assuming these were suitable 64-bit atomic primitives based on the naming.


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