"Tom Linden" <tom@[EMAIL PROTECTED]
> wrote in message
news:ops11ajyr2zgicya@[EMAIL PROTECTED]
> On Mon, 19 Dec 2005 08:54:33 -0500, John W. Kennedy
> <jwkenne@[EMAIL PROTECTED]
> wrote:
>
> > robin wrote:
> >> "John W. Kennedy" <jwkenne@[EMAIL PROTECTED]
> wrote in message
> >> news:T4fpf.39027$L7.8883@[EMAIL PROTECTED]
> >>> MZN wrote:
> >>>> Where I can read detailed description in floating point
implementation
> >>>> on S370 and IEEE-754? Some experts on migration from mainframe here
> >>>> told me that IBM machines had different implementations for
different
> >>>> models of S370 system.
> >>> Some odd models of the S/360 line were different from the others,
and
> >>> there was a large FP re-engineering applied to all machines ca. 1967
or
> >>> so,
> >> This was for the S/360, and it was not major; it involved
> >> adding the guard digit to the Floating-Point arithmetic unit.
> >> It is irrelevant to this case. Its main effect was to
> >> improve accuracy for single precision working. MZN
> >> has been using double precision and extended precision.
> >> Even on S/360 and S/370 the effects on DP operations
> >> were not anywhere noticeable as on single precision.
> >
> > The guard digit was added to double precision, postnormalization was
> > added to the HER and HDR instructions, and the behavior of overflow
and
> > underflow was altered.
>
> As an interesting aside, ICL (as did Siemens) licensed the Spectra
series
> from
> RCA and called it the system 4.
Actually, it was the English Electric Company who did that.
English Electric's computer division along with other British
manufacturers
were merged under the ICL umbrella by c. 1970.
> We had a 4/72 when I worked at the European
> Space Agency in the early 70's and we found that it gave different
results
> for
> orbital calculations than the 360/65 because of the guard digit
producing
> different
> rounding behaviour.
The 4-50 and 4-70 had the guard digit on the single precision instructions
(I don't know about the 4-72, but expect that it was the same being
the more-powerful of the series).
However, neither the 4-50 nor the 4-70 had a guard digit
on the HE, HER, HD, and HDR instructions.
It is surprising that those instructions did not match the D family
floating-point instructions, because the H family was about
from 10 to 30 times faster than the D family.
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