| Donald L. Dobbs 2006-01-14, 6:55 pm |
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glen herrmannsfeldt wrote:
> John W. Kennedy wrote:
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> (snip)
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> That may be true, but the for many numerical algorithms the number of
> bits required increases as the size of the problem increases, which
> likely would have happened in the transition from 7094 to 360.
In the early 1960's when I worked at a Division of North American
Aviation (the aerospace portions now owned by Boeing) we received the
second 360/65 on the West Coast, and we were an IBM beta site for
several of their software products. The biggest headaches we had in
migrating programs from 7094 to 360 were (1) learning job control
language (JCL), and (2) redeclaring Fortran variables from single- to
double-precision where the loss of 4 bits made a difference. Since we
were on cost-plus government-funded projects the efficiency of the 360
in terms of an extra machine cycle per F.P. computation was of
absolutely no consequence monetarily or operationally.
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> If the speed ratio was much smaller on 360 than 7094 that would
> also have helped.
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> (snip)
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> For many algorithms the average number of bits, 22.5, is more
> representative than the minimum. There is always a tradeoff between
> exponent and fraction.
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> There are formats which use an 8 bit exponent followed by the sign and
> fraction. That allows the exponent to be manipulated using byte
> instructions.
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> Mostly I would say that it took more work to come up with algorithms
> suitable for HFP. I explained previously the modification to the SQRT
> algorithm, simple once you know it but someone had to figure that out.
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> (snip)
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> One of the results of designing a machine useful for both fixed and
> floating point problems.
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> -- glen
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