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Re: Implementor support for the binary interchange formats



Date: Tue, 01 Mar 2011 11:34:44 -0500
To: stds-754                      <stds-754@xxxxxxxxxxxxxxxxx>
From: Michel Hack                          <hack@xxxxxxxxxxxxxx>
Subject: RE: Implementor support for the binary interchange formats

Intel people should correct me if needed, but I was under the impression
that Itanium has hardware support for efficient software implementation
of binary128, and is one of the early machines to define what eventually
became the 2008 binary128 standard.

As for COBOL's FLOAT-SHORT, -LONG and -EXTENDED, I suspect they were
mapped to binary32, binary64 and Intel's binary80.  Binary16 has been
defined as a low-precision compact storage format; I know of no uses,
but there may be some in the embedded-system space.

Michel.
---Sent: 2011-03-01 16:45:00 UTC


        Actually, Michel, it is the HP & Sun people who should
        correct you. :-)

        The floating-point type that we called binary128 in the
        2008 standard is identical to the quad floating-point
        type that was used both by HP in their earliest RISC
        machine & Sun in some of theirs.

        I was involved in defining quad for HP & I have become
        friends with those involved in the same thing at Sun.
        There is some friendly dispute as to who came first but
        I like to say that we copied each other.  While I don't
        remember exact dates, I am sure I was working on what
        we called IEEE quad prior to 1988.  Probably as far back
        as 1985 or 1986.  I am less certain about that.  The
        machines ran at 8 MHz if that helps fix the date.

        Both these 128 bit formats & Intel's 80 bit format were
        considered instantiations of 754-1985's Double Extended.
        Intel's being the smallest possible instantiation & ours
        being the smallest instantiation aligned to a 64 bit
        boundary.

        At the time I felt that the 128 bit types naturally made
        more sense.  But over the years I have come to discover
        that making natural sense is overrated.  The 80 bit
        format has turned out to be useful as well.

        Still we in the 754-2008 revision committee thought it was
        time to bless the 128 bit format as basic with the name
        binary128 lest some future architect decided to play games
        with it.  And we admitted both formats to a class of user
        defined formats that we also blessed as conforming.

        Alas, it was also necessary to admit Intel's newer 82 bit
        format as acceptable.  And it must be admitted that it
        was first developed at HP before Intel bought it out.

        Still, some people really like to push unnatural to the
        limit. :-)

        Enjoy,

                                   Dan


        P.S. - Oh, as for full hardware support, the first I am
        aware of is a machine that was designed at HP Labs by
        people we brought over from IBM in a computer architecture
        that was eventually to be sold to Intel as Itanium.  We
        are more inbred than most of us like to admit. :-)


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