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.
|
