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From: "newbie-02 at gmx dot de" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug math/28472] pow(10, i) accuracy
Date: Fri, 23 Sep 2022 16:33:03 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D28472

--- Comment #8 from b. <newbie-02 at gmx dot de> ---

are the following differences based on any reasonable idea? is it of help to
dig down this issue?=20=20

printf( "%.25E\n", pow( 10, 23 ) );  -> 9.9999999999999991611392000E+22=20=
=20

in contrast to:=20=20
int j =3D 23;=20=20
printf( "%.25E\n", pow( 10, j ) );   -> 1.0000000000000000838860800E+23=20=
=20

IMHO the results should match!=20=20

same with 210:=20=20

printf( "%.25E\n", pow( 10, 210 ) ); -> 9.9999999999999992711378242E+209=20=
=20

while:=20=20

j =3D 210;=20=20
printf( "%.25E\n", pow( 10, j ) );   -> 1.0000000000000000731118822E+210=20=
=20

seems independent of j defined as integer or double, and constants written =
as
'x' or 'x.0', but dependent on compiler options:=20=20

no '-Ox' option set or '-O0': above differences,=20=20
'-O1', '-O2' or '-O3' set   : results match, all 9.99999xxx,=20=20

different evaluation at compile- vs. runtime? I seem to remember similar
oddities when a compiler replaces long double constants with doubles at com=
pile
time????=20=20

but why here? me in error? me stupid, me blackout? or is gcc / glibc / ???
kidding with the programmers?=20=20

admit to be confused, esp. about this error being dependent on compiler
options,  while the test program by M Welinder, and gnumeric where the prob=
lem
first came up, are not.

--=20
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