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Date: Tue, 16 May 2023 20:49:11 +0200
From: newbie nullzwei <newbie-02@....de>
To: musl@...ts.openwall.com
Subject: DTOA: question about rendering / code pointer
( apologize - re-tweet - 'plain text', hope that will work better |
apologize - re-tweet - now 'subscribed' - got the impression my
mails didn't make it through to the list while not subscribed? )
hello @ all,
gnumeric uses musl dtoa for rendering, and a self constructed
'brute force' concept to find 'shortet round tripping' figures mostly
similar to https://www.exploringbinary.com/the-shortest-decimal-string-that-round-trips-may-not-be-the-nearest/
we face the same issue as mentioned there, some powers of two
miss to get the shortest 'round tripping' string, but have assigned
another one digit longer string. Forcing to one digit less produces a
string one decimal off in last position, and not tripping back to
the original double.
Example: 0x1p-44 ( 2^-44 ) is rendered to
5.6843418860808015E-14 when allowed 17 digits, for
16 digits it switches to 5.68434188608080**1**E-14, which is
not too bad as the 'exact' decimal weight of the binary representative
is ~5.684341886080801486969E-14, thus undershot to ~15, but!
it points to a different double, and 5.68434188608080**2**E-14
would be a better choice as it round trips to the originating double
value. Affected ~46 integral powers of two in doubles, many more
with long doubles.
Is there any hope musl could change that? provide it as an option?
Or can anyone give a code pointer or nearer explanation to enable
us to patch it for our 'exotic' use?
best regards, TIA for any help.
b.
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