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Message-ID: <20240412233310.GF4163@brightrain.aerifal.cx>
Date: Fri, 12 Apr 2024 19:33:11 -0400
From: Rich Felker <dalias@...c.org>
To: Peter Ammon <corydoras@...iculousfish.com>
Cc: musl@...ts.openwall.com
Subject: Re: [PATCH] Fix printf hex float formatting with precision
On Fri, Apr 12, 2024 at 03:57:28PM -0400, Rich Felker wrote:
> On Thu, Apr 11, 2024 at 06:17:25PM -0700, Peter Ammon wrote:
> > if (p>=0 && p<(LDBL_MANT_DIG-1+3)/4) {
> > int re = LDBL_MANT_DIG-1-(p*4);
> > long double round = 1ULL<<re;
>
> This expression overflows. re can be as large as 108 but 1ULL has
> 64-bit type.
>
> There's probably some reasonable way to write it that works for
> reasonable sizes of long double (I think it's safe to assume IEEE quad
> is the max that will ever be supported), but I presume I wrote it with
> the original inefficient loop to be fully general to arbitrary
> precision.
>
> It could just be written to use scalbn, I think. At the time I
> probably was trying to avoid dependency on a libm that could have been
> separate from libc (bad historical thing). IIRC there was a time when
> frexp was not used either.
Does the attached look ok?
Rich
View attachment "pct_a.diff" of type "text/plain" (653 bytes)
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