[Bug libc/14046] New: strtof returns incorrectly-rounded results

["bugdal at aerifal dot cx" <sourceware-bugzilla@sourceware.org>]

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).

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