From: Markus Wichmann <nullplan@gmx.net>
To: musl@lists.openwall.com
Cc: Viktor Reznov <yann.collet.is.not.a.perfectionist@gmail.com>
Subject: Re: [musl] [PATCH] Decreasing the number of divisions
Date: Tue, 16 Apr 2024 16:29:12 +0200 [thread overview]
Message-ID: <Zh6LOBFx8ZCjHFTO@voyager> (raw)
In-Reply-To: <CAKs8_OLhgp8OaeOdYs3+LZShS21-s7C3=3Tzo_Mj31dVL_i9_g@mail.gmail.com>
Am Tue, Apr 16, 2024 at 04:29:05PM +0300 schrieb Viktor Reznov:
> diff --git a/src/stdio/vfprintf.c b/src/stdio/vfprintf.c
> index 497c5e19..0f9a1e6a 100644
> --- a/src/stdio/vfprintf.c
> +++ b/src/stdio/vfprintf.c
> @@ -165,8 +165,10 @@ static char *fmt_o(uintmax_t x, char *s)
> static char *fmt_u(uintmax_t x, char *s)
> {
> unsigned long y;
> + if (x == 0) return s;
> for ( ; x>ULONG_MAX; x/=10) *--s = '0' + x%10;
> - for (y=x; y; y/=10) *--s = '0' + y%10;
> + for (y=x; y>=10; y/=10) *--s = '0' + y%10;
> + *--s = '0' + y;
> return s;
> }
I played around with this change on godbolt: https://godbolt.org/z/9PoGK9zae
Seems to me like the version with OPTIMIZE=1 is longer and more
complicated.
OK, let's take a step back: What is the point of this patch? It makes
the code longer and less readable. It does not fix a logic bug. The only
reason I can see is that it makes the code "faster". In that case, I
would like to see a benchmark.
On x86-64, the loop condition on the first loop is always false, so the
unchanged function becomes a single loop. The changed function becomes a
selection statement, a loop, and an assignment. Don't see how that could
possibly be faster. But am willing to be convinced otherwise.
Ciao,
Markus
next prev parent reply other threads:[~2024-04-16 14:29 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-16 13:29 Viktor Reznov
2024-04-16 14:29 ` Markus Wichmann [this message]
2024-04-17 1:25 ` NRK
2024-04-17 1:56 ` Markus Wichmann
2024-04-16 14:38 ` Rich Felker
[not found] ` <CAKs8_OKqKsLbG_Cf0DtDGeZDLdFkO1kDx6z5Fg_rQwPxPLGP6g@mail.gmail.com>
2024-04-16 16:55 ` Rich Felker
[not found] ` <CAKs8_OJ4evmTzAGVZ1Yccw+4Jj7v=RwEJWicwbSoeQwbvqav1Q@mail.gmail.com>
2024-04-17 0:09 ` [musl] " Rich Felker
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