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"John W. Kennedy" <jwkenne@attglobal.net> wrote in message
news:s7Vpf.39983$L7.34049@fe12.lga...
> robin wrote:
>
> The main intention of the HER and HDR instructions was to accelerate
> taking square roots.
First time I have heard of that one.
Division by 2 was and still is a fairly common operation
(averaging, etc) and given that float division took
an extraordinarily long time, HER and HDR were
golden opportunities to speed up algorithms, if only
compilers would use them.
> It is very well known that the entire 360 FP feature could have used
> some input from numerical analysts; it's shot full of design defects.
When the S/360 was designed (1964), hardware was expensive,
and a hexadecimal mantissa minimised the hardware and,
in particular, reduced shifting time [for normalization] to
a minimum.
> Some of the mistakes were corrected in the 1967 re-engineering, but
> others (most grossly, the hexadecimal orientation) had to wait for IEEE-754.
Like I said, hex mantissa was a design that maximised speed and
minimised cost. IMHO it was a reasonable compromise.
> --
> John W. Kennedy
> "But now is a new thing which is very old--
> that the rich make themselves richer and not poorer,
> which is the true Gospel, for the poor's sake."
> -- Charles Williams. "Judgement at Chelmsford"
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