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Problem Report 1638 Details

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Report 1638 Actions

    Problem Report Number 1638
    Submitter's Classification Test Suite problem
    State Resolved
    Resolution Permanent Interpretation (PIN)
    Problem Resolution ID PIN.X.0195
    Raised 2000-03-08 08:00
    Updated 2003-03-13 08:00
    Published 2000-03-23 08:00
    Product Standard Internationalised System Calls and Libraries Extended V2 (UNIX 98)
    Certification Program The Open Brand certification program
    Test Suite VSU version 5.0.4
    Test Identification CAPI.os/maths/ilogb 2
    Specification System Interfaces and Headers Issue 5
    Location in Spec See Problem Text
    Problem Summary PIN4U.00061 This interpretation allows ilogb(0) to return INT_MIN for UNIX98.
    Problem Text
    This test is failing as our implementation returns INT_MIN for
    ilogb(0) and the expected value is -INT_MAX. INT_MIN is the value
    expected by XSH, Issue 4, Version 2. PIN4U.00037 was granted against
    XSH4.2 and the request claimed that the value returned should be -INT_MAX,
    stressing historical reasons and representational problems in a
    one's complement architecture. This called for a change to the spec.

    Apparently an error was made while changing the specification for
    XSH Issue 5, and it says the return value should be -INT_MIN, which
    is obviously wrong. Since the test is not aligned with the specifications
    and there is no corrigendum to correct this situation, we would request
    that a TSD be granted for this test.

    Test Output
    TEST PURPOSE #2
    A call to int ilogb(double x) when x is 0 shall return
    -INT_MAX.
    TEST: ilogb(0) returns -INT_MAX
    ERROR: ilogb(0) returned incorrect value
    Expected -INT_MAX
    Received -2147483648
    2 FAIL

    Review Information

    Review Type TSMA Review
    Start Date null
    Completed null
    Status Complete
    Review Recommendation No Resolution Given
    Review Response
    The specification issues pertaining to this test are as follows:

    1. In XSH4.2 the requirement was for ilogb(0) to return INT_MIN.

    2. The intended requirement for UNIX98, as stated in PIN4U.00037,
    was for ilogb(0) to return -INT_MAX.

    3. This intended future direction was not implemented correctly in
    the published version of XSH5. Instead XSH5 requires the
    return of -INT_MIN, which is impossible on some architectures
    (including the most common one).

    4. The new 1999 C Standard allows ilogb(0) to return either INT_MIN
    or -INT_MAX, and a future revision of XSH will no doubt align
    with C99. (Although this does not automatically mean the XSH
    revision would allow both - it could impose a restriction to
    only one of the behaviours allowed by C99.)

    Since returning INT_MIN was required for UNIX95, and is allowed by the
    current C Standard, it is recommended that a permanent interpretation
    is granted to allow this behaviour for UNIX98. However, this matter
    should first be reviewed by the base working group.

    Review Type SA Review
    Start Date null
    Completed null
    Status Complete
    Review Resolution Permanent Interpretation (PIN)
    Review Conclusion
    A Permanent Interpretation is granted.

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