Re: [boost] Fixed-Point Decimal Type

From: Gabriel Dos Reis (Gabriel.Dos-Reis_at_[hidden])
Date: 2001-05-21 18:24:59

John Max Skaller <skaller_at_[hidden]> writes:

| 	My 'gut feeling' on this is that the basic
| calculations don't involve rounding at all. 
| They're exact. 

They are exact only if there is no overflow using a grammar school
algorithm.  However, intermediate results can overflow whereas
the exact final result could be represented in the given floating
point datatype as you acknowledge it here:

| ... One problem with this approach
| is that overflow on multiply occurs before rounding:
| if the rounding is 'built-in' to the multiply, it is possible
| to avoid overflow in some cases:
| 
| 	decimal<n> mul<n>(decimal<n> a, decimal<n> b)
| 
| is more general and could avoid overflows (by, for example,
| scaling the arguments first, before multiplying).

And that situation is not uncommon. 

Yes. That is why a trait-based solution can give best of both worlds. 

-- Gaby