Fix strtod rounding of hex values (bug 14049)

[Andreas Jaeger]

On 05/02/2012 06:48 PM, Joseph S. Myers wrote:
> The strtod implementation, when handling a hexadecimal value with more
> digits than needed to compute the mantissa, passes a value "dig_no>
> 0" as the last argument to round_and_return.  The meaning of this
> argument is whether any subsequent bits (after the mantissa and
> subsequent MP limb that includes at least the half-ulp bit) are
> nonzero.
>
> dig_no here counts the number of remaining digits *including* the one
> being processed, so is always positive here and half-way values always
> get rounded away from zero.  Furthermore, while trailing zeros after
> '.' have been excluded from consideration earlier, those before '.'
> have not.
>
> I propose this patch to fix this bug by checking the rest of the
> string for nonzero digits.  Because of the earlier handling of
> trailing zeros, there is no need to check for '.' here; if it occurs
> before dig_no becomes 0, there must be a nonzero digit after the '.'
> (and so '.' can be treated like a nonzero digit).  Tested x86_64.
>
> 2012-05-02  Joseph Myers<joseph@codesourcery.com>
>
> 	[BZ #14049]
> 	* stdlib/strtod_l.c (____STRTOF_INTERNAL): Check for trailing
> 	nonzero digits before rounding a hex value.
> 	* stdlib/tst-strtod.c (tests): Add another test.

thanks, this is fine,

Andreas
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