Re: Possible improvements to the LNUM patch?

[Asko Kauppi <askok@...>]

The original LNUM had also a BCD mode, which was removed for  
simplicity. I wanted to see, how far the number modes concept could  
go, and drew a line between complex (included, since C99 offers great  
help on this) and BCD (which would need lots of code, or outside  
library).

If there's a good enough, free BCD library out there, adding it to  
LNUM would not be too hard.

In my opinion, the number of decimals should be a compile time option  
(i.e. -DLNUM_BCD_DECIMALS=5).

Most likely, all mathematics should be BCD in such a mode. No floating  
point usage, whatsoever. Right?  Otherwise, I'd simply recommend doing  
BCD as an add-on Lua side module.

( Oh, and instead of BCD of course it would use fixed point decimal.  
BCD is just a loose storage form, which does not provide benefits in  
this case, to my understanding. )

-asko


Aladdin Lampé kirjoitti 14.4.2008 kello 20:38:
> Hi Lua list!
>
> I would like to use Lua in a "financial" context, where using  
> "doubles" for floating point decimal numbers is not enough regarding  
> to precision.
> Indeed, dealing with large monetary values may trigger overflows in  
> the calculations... I certainly do not want this to happen.
>
> Is there a way, using the LNUM patch, to circumvent this? I have  
> thought about using an int64 for numbers and associating a second  
> number to indicate where the decimal point is located. Another  
> option would be to use BCD like some databases do (ORACLE for  
> instance) to deal with arbitrary precision decimals.
>
> What do you think? Is LNUM the way to go (with some improvements),  
> or should I instead use some available BCD library? (or implement it  
> by myself).
>
> Thanks for any insight.
> Aladdin
>
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