[Bug 1001628] New: %g printf format prints more digits than expected

[Bug 1001628] New: %g printf format prints more digits than expected

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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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[Bug 1001628] %g printf format prints more digits than expected

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Bernd Edlinger <bernd.edlinger@hotmail.de> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
               Flag|                            |Patch_or_Contribution+

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[Bug 1001628] %g printf format prints more digits than expected

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Bernd Edlinger <bernd.edlinger@hotmail.de> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Attachment #1841|0                           |1
           is patch|                            |

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[Bug 1001628] %g printf format prints more digits than expected

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--- Comment #1 from Bernd Edlinger <bernd.edlinger@hotmail.de> 2012-08-11 07:28:22 BST ---
see bug #20804 for a cumulative patch that fixes several issues, including the
%g format.

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[Bug 1001628] New: %g printf format prints more digits than expected

[bugzilla-daemon]

Please do not reply to this email. Use the web interface provided at:
http://bugs.ecos.sourceware.org/show_bug.cgi?id=1001628

           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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