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Problem Report 0487 Details

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Report 0487 Actions

    Problem Report Number 0487
    Submitter's Classification Test Suite problem
    State Resolved
    Resolution Rejected (REJ)
    Problem Resolution ID REJ.X.0106
    Raised 1995-07-20 08:00
    Updated 2003-03-13 08:00
    Published null
    Product Standard Internationalised System Calls and Libraries (XPG4)
    Certification Program The Open Brand certification program
    Test Suite VSX4 version 4.3.5
    Test Identification XPG4.hdr/misc/float 4
    Problem Summary PG4R.107 Test makes underlying hardware assumption. We fail this test case because the test suite expects the floating-point (FP) model defined in <float.h> to equal the precision of the underlying hardware. I...
    Problem Text
    Test makes underlying hardware assumption.

    We fail this test case because the test suite expects the floating-point
    (FP) model defined in <float.h> to equal the precision of the underlying
    hardware.

    In looking at section 2.2.4.2.2 of the ANSI C standard, we see no
    requirement for the values defined in <float.h> to equal the maximum
    possible value the hardware can represent. All values included in
    <float.h> are defined in terms of the FP model. Our FP model is well
    documented and meets the requirements of the ANSI C standard. The test
    suite should not test for behavior outside the scope of the base
    standard.

    We believe this test should be changed to verify that the computed
    values are greater-than-or-equal in magnitude (absolute value) to
    the values defined in <float.h>. This will verify the FP model and
    not the hardware.
    Test Output
    ************************************************************************
    /tset/XPG4.hdr/misc/float/T.float 4 Failed

    Test Description:
    When the values for the following symbolic names can be determined
    arithmetically, then the symbolic names evaluate to the same value:
    FLT_DIG, DBL_DIG, LDBL_DIG, FLT_MIN_EXP, DBL_MIN_EXP, LDBL_MIN_EXP,
    FLT_MIN_10_EXP, DBL_MIN_10_EXP, LDBL_MIN_10_EXP, FLT_MAX_EXP,
    DBL_MAX_EXP, LDBL_MAX_EXP, FLT_MAX_10_EXP, DBL_MAX_10_EXP,
    LDBL_MAX_10_EXP, FLT_MAX, DBL_MAX, LDBL_MAX, FLT_EPSILON, DBL_EPSILON,
    LDBL_EPSILON, FLT_MANT_DIG, DBL_MANT_DIG, LDBL_MANT_DIG, FLT_MIN,
    DBL_MIN, LDBL_MIN and FLT_RADIX.

    Test Information:
    Feature test macros: -D_XOPEN_SOURCE
    Compiler or run-time messages or results:
    Value of FLT_MIN_EXP is incorrect
    Observed: -8189
    Expected: -8192
    Value of FLT_MIN is incorrect
    Observed: 3.66720773511e-2466
    Expected: 0
    Value of FLT_MIN_10_EXP is incorrect
    Observed: -2465
    Expected: -2466
    Value of FLT_DIG is incorrect
    Observed: 13
    Expected: 14
    Value of FLT_MANT_DIG is incorrect
    Observed: 47
    Expected: 48
    Value of DBL_MIN_EXP is incorrect
    Observed: -8189
    Expected: -8192
    Value of DBL_MIN is incorrect
    Observed: 3.66720773511e-2466
    Expected: 0
    Value of DBL_MIN_10_EXP is incorrect
    Observed: -2465
    Expected: -2466
    Value of DBL_DIG is incorrect
    Observed: 13
    Expected: 14
    Value of DBL_MANT_DIG is incorrect
    Observed: 47
    Expected: 48
    Value of LDBL_MIN_EXP is incorrect
    Observed: -8189
    Expected: -8192
    Value of LDBL_MIN is incorrect
    Observed: 3.66720773510972502543901904e-2466
    Expected: 0
    Value of LDBL_MIN_10_EXP is incorrect
    Observed: -2465
    Expected: -2466
    Value of LDBL_DIG is incorrect
    Observed: 27
    Expected: 28
    Value of LDBL_MANT_DIG is incorrect
    Observed: 94
    Expected: 96
    ************************************************************************

    Review Information

    Review Type TSMA Review
    Start Date null
    Completed null
    Status Complete
    Review Recommendation No Resolution Given
    Review Response
    There are two separate issues here. The first is the claim by the
    submitter that the values defined in <float.h> do not have to reflect
    the hardware capabilities of the implementation. This may be a valid
    question for some <float.h> values, but not for others. For example
    the values of FLT_EPSILON, DBL_EPSILON and LDBL_EPSILON are defined to
    be "the difference between 1.0 and the least value greater than 1.0 that
    is representable in the given floating-point type." It seems clear
    that these values must reflect the floating point representation used
    for the types float, double and long double in the way specified.
    However for values such as FLT_MIN_EXP, DBL_MIN_EXP and LDBL_MIN_EXP the
    definition is only given in terms of the model, and it may be that
    implementors can have a some degree of choice in defining these values.
    This is a matter that should be decided through the C standard
    interpretations process.

    The second issue is the claim by the submitter that the values defined
    in <float.h> meet the requirements of the model. Since the test has not
    reported that FLT_EPSILON is incorrect, this raises the question of
    whether the implementation meets the requirement that FLT_EPSILON is
    equal to FLT_RADIX raised to the power of (1 - FLT_MANT_DIG), and likewise
    for DBL_EPSILON and LDBL_EPSILON. It will be necessary to ask the
    submitter to supply these values in order to verify this.

    It recommended that this request be refused on the grounds that further
    supporting information is needed. If this is supplied in a resubmission
    of this request, and is found to be satisfactory, then a temporary
    interpretation should be granted, pending an ISO C interpretation.

    Review Type SA Review
    Start Date null
    Completed null
    Status Complete
    Review Resolution Rejected (REJ)
    Review Conclusion
    This request is refused. Please refer to TIN4.010.

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