[LLVMbugs] [Bug 11406] New: floating-point constant expressions are incorrectly rounded

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Sat Nov 19 14:07:50 PST 2011


             Bug #: 11406
           Summary: floating-point constant expressions are incorrectly
           Product: clang
           Version: trunk
          Platform: PC
        OS/Version: FreeBSD
            Status: NEW
          Severity: normal
          Priority: P
         Component: Frontend
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: das at freebsd.org
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Created attachment 7629
  --> http://llvm.org/bugs/attachment.cgi?id=7629

In the default floating-point rounding mode (IEEE round-to-nearest), halfway
cases are supposed to round to the nearest *EVEN* representable number, but in
clang, apparently they don't always do that.

The attached program prints 0x1.0000000000001p+0 when compiled with clang -O,
but it prints 0x1.0p+0 when compiled with gcc or clang -O0, or when 'd' is
declared volatile.  0x1.0p+0 is the correct answer.

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