[Coco] printing out floating point numbers...(only peripherally related to coco)

[jdaggett at gate.net]

Aarron

Sorry if you are offended. My first impression of someone asking for 
mathematical manipulation of two or more 70+ decimal digit precission is 
either, one doesn't know what they are asking for or second the orginal 
message was a joke. Thus my reply was to honestly figure out which.  I 
have also gathered that you appear serious. I still do not understand your 
need for such precision but then you must have your reasons. I have 
worked in engineering for 23 y rs and have done numerous computer 
modeling and have yet to find a need to do floating point numbers with that 
kind of precission. 245 bits of precision on the mantissa should yield a 
decimal fraction to around 70 decimal places. I have yet to see a reall need 
to to express a fractional part of 70 decimal places with an exponential 
part. Even in measuring distances between quarks do not need this kind of 
precission.  

But then to each  his own. Once you have justified the exponents, the math 
is then rather simple. Addition and subtraction, preferably by twos 
compliment addition,  can be done over a series of additions  with carry. 
Multiplication can be done by partial products and accumalate the partial 
sums to gain the final answer. Division is s bit more touchy. You have to 
change the sign of the exponent and substract one. Also the inverse of the 
mantissa needs to be calculated and then use multiplication. 

Remember that to add and substract FP # you need to have both at the 
same exponent. Multiplication and division is not needed. 

james

On 12 Jul 2006 at 19:38, Aaron Banerjee wrote:

> 
> Quite simple. I'm working with numbers which are in a relatively small
> range, but need a fine degree of precision.  As others have mentioned,
> this is sort of an odd size for a float.  I wasn't looking for a generic
> super-float.  Depending on what you're using it for, 8 bit mantissa and
> 245 bits of precision isn't "absurd" at all.
> 
> To everyone except for James, thanks.  You've given me a good place to
> start.
>                      - Aaron
> 
> On Wed, 12 Jul 2006 jdaggett at gate.net wrote:
> 
> > First off why do you need 245 bits in the mantissa when you limit yourself to only 8 
> > bits in the exponent? Do you really need  70+ decimal digit precission when you 
> > exponet is limited to 38 places decimal? 
> > 
> > There is precission and then there is taking precision to nth degree of absurdity. I 
> > think 245 bits in the mantissa is fast approaching absurdity with only 8 bits in the 
> > exponent.
> > 
> > just my opinion 
> > 
> > james
> 
> 
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