Tom Linden wrote:
> On Thu, 19 Jan 2006 11:31:46 -0500, John W. Kennedy
> <jwkenne@[EMAIL PROTECTED]
> wrote:
>
>> Randy Hudson wrote:
>>> In article <pqizf.1906$EU3.1442@[EMAIL PROTECTED]
>,
>>> John W. Kennedy <jwkenne@[EMAIL PROTECTED]
> wrote:
>>>
>>>>>>> When I last looked, 27 + 1 + 7 + 1 = 36.
>>>>>> Are you under the impression that the 704 series had a 35-bit word
>>>>>> with
>>>>>> a parity bit?
>>>>> You said 36 bits earlier.
>>>> Yes, I did, because it /did/ have 36. But your breakdown above
>>>> includes an extra 1-bit field that cannot be accounted for.
>>> There's two sign bits: sign of mantissa, and sign of exponent.
>>> "Excess"
>>> representation of the exponent hides the explicit sign, but the bit
>>> is still
>>> effectively a sign.
>>
>> In forty years, I have yet to see one single hardware manual that
>> describes it so.
>>
>>> Also, with binary floating point, a normalized mantissa would always
>>> have a
>>> 1 as the leftmost bit, so in most implementations, that's assumed and
>>> overwritten by the sign bit.
>>
>> That's a relatively modern sophistication, and definitely not
>> applicable to the vacuum-tube and discrete-transistor eras.
>>
> I don't believe that is true, I believe most floating point
> representations that
> have used a binary exponent have suppressed the leading one to obtain
> one more
> bit of accuracy. But with a radix 16 exponent you can't. of course do
> that.
>
> Not sure how far this goes back in time, but i bet it is to the 50's
> anyway.
At the very least, it is /not/ the case in the IBM
704/709/7040/7044/7090/7094 family, which is the architecture that
FORTRAN was designed for, the architecture under discussion in this
subthread, and the most im****tant scientific architecture previous to
the 360.
--
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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