Robin,
>> Date: Wed, 17 Oct 2001 15:22:26 -0400
>> From: Bob Cohen <[log in to unmask]>
>
>> At 02:38 PM 10/17/01 +0200, you wrote:
>
>> (I've always assumed Double Precision meant ~ 16 digits of accuracy.
>
>If a word of 32 bits is used for single precision,
>then double precision uses 64 bits.
> In those 32 or 64 bits, an exponent is stored as well as the mantissa
>(or
>significand).
> In some systems, the exponent takes 8 bits, with an effective
>mantissa
>of 21 bits for single precision and 53 bits for double precision.
>Thus single precision is about 6 decimal digits and double precision is about
>16 decimal digits (on those systems).
> But there have been other word sizes over the years -- including
>36 bits and 60 bits, with 72 and 120 bits being used for double precision
>respectively.
>
>> It
>> was quite upsetting to learn that a Lotus Spreadsheet could do it just
>> fine. I believe that the spreadsheet has 18 digits of precision. I
>> could have used 128 bit reals at that time.
Sorry about the messy chevron stuff, it's how the mail came to me.
This thread is blithely talking about 32/64 bits. Aren't we really interested
in the precision of the mantissa? On the OS I use, there are two levels of
double precision. The difference being an extra bit in the exponent and one
less in the mantissa. (Or vice versa :-)
Generally, we are talking about 23/53 mantissa bits for precision.
Regards, Paddy
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