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From: Achim Gratz <Stromeko AT nexgo DOT de>
To: cygwin AT cygwin DOT com
Subject: Re: gcc 11.1.0: printf("%.43f\n", 0x1.52f8a8e32e982p-140): printed
 value is incorrectly rounded
References: <CAL9Mx1uMOz2wfqbMpD_xfA=D9JkpFzVz6AR_DKHK34AvrGOP6w AT mail DOT gmail DOT com>
Date: Sun, 13 Jun 2021 11:42:38 +0200
In-Reply-To: <CAL9Mx1uMOz2wfqbMpD_xfA=D9JkpFzVz6AR_DKHK34AvrGOP6w@mail.gmail.com>
 (Pavel M. via Cygwin's message of "Sat, 12 Jun 2021 23:45:54 +0300")
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Pavel M via Cygwin writes:
> Sample code (t903.c):
> #include <stdio.h>
> int main(void)
> {
>     printf("%.43f\n", 0x1.52f8a8e32e982p-140);
>     return 0;
> }
>
> Invocations:
> # gcc on Windows 10 (Cygwin)
> $ gcc t903.c -Wall -Wextra -std=c11 -pedantic -Wfatal-errors && ./a.exe
> 0.0000000000000000000000000000000000000000010

You will want to report this against newlib, I'd think.  If I remember
correctly, newlib uses a single guard digit for the conversion and for
such an algorithm the result you see is expected and correct.  Whether
any later C standard would mandate to use an algorithm that uses higher
precision (in terms of guard digits you'd end up with 15 for your
example before you get the expected result I think) I have no idea.


Regards,
Achim.
-- 
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+

SD adaptation for Waldorf rackAttack V1.04R1:
http://Synth.Stromeko.net/Downloads.html#WaldorfSDada

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