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[Bug 1001628] New: %g printf format prints more digits than expected
- From: bugzilla-daemon at bugs dot ecos dot sourceware dot org
- To: ecos-bugs at ecos dot sourceware dot org
- Date: Tue, 24 Jul 2012 18:43:14 +0100
- Subject: [Bug 1001628] New: %g printf format prints more digits than expected
- Auto-submitted: auto-generated
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Summary: %g printf format prints more digits than expected
Product: eCos
Version: CVS
Platform: All
OS/Version: All
Status: UNCONFIRMED
Severity: normal
Priority: low
Component: C library
AssignedTo: unassigned@bugs.ecos.sourceware.org
ReportedBy: bernd.edlinger@hotmail.de
CC: ecos-bugs@ecos.sourceware.org
Class: Advice Request
Created an attachment (id=1841)
--> (http://bugs.ecos.sourceware.org/attachment.cgi?id=1841)
a proposed patch to fix this defect
when a printf format like "%.7g" is used, you would expect
to see at most 7 valid decimals. But if the value is very close
to an integer like (float)5.000123 the output may look like "5.000123xxxx"
with xxxx = 4 additional digits which contain only rounding errors.
The correct output would be "5.000123", which is 7 valid digits.
The reason is in "language/c/libc/stdio/current/src/output/vfnprintf.cxx",
where the loop termination assumes the number of leading digits (in expcnt)
to be zero, which is not always the case however.
To fix this use the attached patch file.
The patch also introduces an additional test case in
"language/c/libc/stdio/current/tests/sprintf2.c",
which will only succeed when the printf format is output correctly.
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