Re: [boost] Fixed-Point Decimal Type

From: Daniel Frey (daniel.frey_at_[hidden])
Date: 2001-05-15 11:05:39

Gabriel Dos Reis wrote:
> 
> Beman Dawes <bdawes_at_[hidden]> writes:
> 
> |  >    This is problematic. For some operations, it is
> |  >wrong to always round 1/2 LSD up: when doing statistical
> |  >operations, rounding up or down at random is correct.
> |  >Sometimes, truncation is correct (rather than rounding).
> |  >
> |  >    This suggests that you pick one mode (as you have)
> |  >for the operator?? forms, but supply the other operations
> |  >as named functions, for example
> |  >
> |  >    mul_with_truncate(a,b)
> |  >    mul_with_rhlsd_up(a,b)
> |  >    mul_with_rhlsd_ran(a,b)
> |  >    mul_with_noround(a,b)
> |
> | Maybe.  But maybe just stick with one form of rounding, unless there really
> | is some overwhelming need for additional forms.
> 
> I think the ability of choosing rounding mode should not be
> overlooked.  It is an essential part of LIA-1 and later standards.

In finance there is another, sometimes important way of rounding: On a
tie, round so that the last digit is even. To illustrate that:

0.249 rounds to 0.2
0.25  rounds to 0.2
0.251 rounds to 0.3
0.349 rounds to 0.3
0.35  rounds to 0.4
0.351 rounds to 0.4

A decimal class can be very useful in this sector, so I consider the
rounding-issue as very important.
 
Regards, Daniel

--
Daniel Frey
aixigo AG - financial training, research and technology
Schloß-Rahe-Straße 15, 52072 Aachen, Germany
fon: [phone], fax: [phone]
eMail: daniel.frey_at_[hidden], web: http://www.aixigo.de