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From: "jacob at jacob dot remcomp.fr" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/107370] long double sqrtl constant folding is wrong
Date: Mon, 24 Oct 2022 20:51:51 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107370

--- Comment #16 from jacob navia <jacob at jacob dot remcomp.fr> ---
Sorry but the program I used was compiled with gcc. It suffers from lack of
precision too.

In ANY case, in decimal now, the square root of 2 is
1.414 213 562 373 095 048 801 688 724 209 698 078 GP PARI calculator
1.414 213 562 373 095 145 547 462 185 874 gcc: only the first 15 digits are=
 OK
                     ^^^^^=20
In ANOTHER example:
#include <stdio.h>
#include <math.h>

int main(void) { printf("%.30Lg \n",sqrtl(powl(2,225))); }

This produces:
7.34301663720716943338259962711e+33
But bc produces=20
~/lcc/book/test % bc
bc 1.06
Copyright 1991-1994, 1997, 1998, 2000 Free Software Foundation, Inc.
This is free software with ABSOLUTELY NO WARRANTY.
For details type `warranty'.=20
scale=3D32
sqrt(2^225)
7343016637207168931428032607349397.48923080385562326502615381523522

To make things clearer I put now the results side by side
7.34301663720716943338259962711e+33 gcc
734301663720716 8931428032607349397.48923080385562326502615381523522 bc

As you can see, after the 15th digits all others are wrong!!!

Jacob=