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Please read before Thursday's meeting...



        Here are my notes from Wednesday's meeting.  If you read it
        before Thursday it will save me having to read it to you during
        the meeting.  Thanks.  - Dan

        ---------------------------------------------------------------

        Notes for meeting at Hewlett Packard in Palo Alto on Wednesday
        7/13/05 in the Von Neumann Room in Building 4.  Peter Markstein
        hosted us.  Dick Delp, Mike Cowlishaw, Jim Thomas, David Hough,
        & Dan Zuras attended.  Eric Schwartz, Mark Erle, & Jeff Kidder
        were on the phone.


        We started with the draft review & finished around 2:20.

        We began with debug.txt (1-6).  People generally seem to think
        its too vague to move into the body of the draft for now.

        Next: snan.htm (2-6).  To make signalling NaNs (& now trapping
        NaNs) optional.  There have been objections raised from the sNaN
        column.  Some also object to the introduction of an optional
        trapping NaN for various reasons.

        Next: static-modes.htm (2-5).  To apply modes (rounding, et al)
        statically.  Mike objected on the grounds that an interpretive
        language can be purely dynamic in its scoping rules.  This
        'meta' problem can be used by sufficiently malicious programmers
        to conceal a change of modes that defeats any reasonable notion
        of 'static'.  We ended up discussing that rather than a static
        mode what we really have in mind that the programmer should have
        the expressive power to say (a) I would like this operation/
        expression/block to be evaluated in this precision/rounding/
        exception mode, or (b) I would like it to be evaluated as if
        some mode change (external to me) would apply to this code, or
        (c) I don't care.  Also this should be a requirement & therefore
        a SHALL.  Making it a SHOULD would defeat the purpose.  We also
        discussed just how 'paranoid' a compiler should be about the
        convention that function calls don't change some global mode.
        The reckless level would be to not know & not care.  The truely
        paranoid level would be to save & restore all modes on the
        procedure call.  Jim argued that an adequate level of paranoia
        was to not move code around function calls.  While that seems
        practical is seems barely more than reckless to me.

        Next: resumable.htm (1-5).  Resumable modes are abrupt
        underflow, presubstitution, & the scaled product functions (in
        lieu of counting mode).  We spent some time discussing whether
        the definition of operations which take arrays as operands or
        used unusual arithmetic in the intermediates.  There is an
        obvious ULP*(N/2) error bound on the result & we would like it
        to be unbiased but its not clear how to both specify & test
        that.  Jeff was also concerned that the product of a great many
        numbers which can be arrived at exactly SHOULD be computed
        exactly.

        Next: nonresumable.htm (1-2).  Nonresumable modes could be
        implemented by some sort of try/catch mechanism.

        Dave mentioned that he withdrew the user trap proposal as it is
        largely covered by the resumable trap proposal.

        We adjourned around 4:30.

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