public inbox for glibc-bugs@sourceware.org
help / color / mirror / Atom feed
* [Bug libc/14046] New: strtof returns incorrectly-rounded results
@ 2012-05-02 2:07 bugdal at aerifal dot cx
2012-05-02 10:01 ` [Bug libc/14046] " jsm28 at gcc dot gnu.org
2014-06-25 11:09 ` fweimer at redhat dot com
0 siblings, 2 replies; 3+ messages in thread
From: bugdal at aerifal dot cx @ 2012-05-02 2:07 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=14046
Bug #: 14046
Summary: strtof returns incorrectly-rounded results
Product: glibc
Version: unspecified
Status: NEW
Severity: normal
Priority: P2
Component: libc
AssignedTo: unassigned@sourceware.org
ReportedBy: bugdal@aerifal.cx
CC: drepper.fsp@gmail.com
Classification: Unclassified
Test case:
"0.000000000000000000000000000000000000000000002101947696487225606385594374934874196920392912814773657635602425834686624028790902229957282543182373046875"
This is the decimal value of 0x1.8p-149, the value exactly halfway between the
smallest two positive single-precision floating point values. It has more than
DECIMAL_DIG significant digits, so it should round as follows:
"If the subject sequence D has the decimal form and more than DECIMAL_DIG
significant digits, consider the two bounding, adjacent decimal strings L and
U, both having DECIMAL_DIG significant digits, such that the values of L, D,
and U satisfy L <= D <= U. The result should be one of the (equal or adjacent)
values that would be obtained by correctly rounding L and U according to the
current rounding direction, with the extra stipulation that the error with
respect to D should have a correct sign for the current rounding direction."
Here L="0.00000000000000000000000000000000000000000000210194769648722560638"
and U="0.00000000000000000000000000000000000000000000210194769648722560639".
Correctly rounded, they should be 0x1p-149 and 0x1p-148, respectively, but
strtof rounds all three (D,L,U) to 0x1p-149.
This is just the particular case I thought to check; surely there are many
others, possibly without even going into the denormal range (which was the
first place I thought to look for bugs).
--
Configure bugmail: http://sourceware.org/bugzilla/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are on the CC list for the bug.
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2014-06-25 11:09 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2012-05-02 2:07 [Bug libc/14046] New: strtof returns incorrectly-rounded results bugdal at aerifal dot cx
2012-05-02 10:01 ` [Bug libc/14046] " jsm28 at gcc dot gnu.org
2014-06-25 11:09 ` fweimer at redhat dot com
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).