float equality

[Andrei Alexandrescu]

On 2/21/11 4:48 AM, Jonathan M Davis wrote:
> On Monday 21 February 2011 01:55:28 Walter Bright wrote:
>> Kevin Bealer wrote:
>>> 1. To solve the basic problem the original poster was asking -- if you
>>> are working with simple decimals and arithmetic you can get completely
>>> accurate representations this way.  For some cases like simple financial
>>> work this might work really well. e.g. where float would not be because
>>> of the slow leak of information with each operation.  (I assume real
>>> professional financial work is already done using a (better)
>>> representation.)
>>
>> A reasonable way to do financial work is to use longs to represent pennies.
>> After all, you don't have fractional cents in your accounts.
>>
>> Using floating point to represent money is a disaster in the making.
>
> Actually, depending on what you're doing, I'm not sure that you can legally
> represent money with floating point values. As I understand it, there are definite
> restrictions on banking software and the like with regards to that sort of thing
> (though I don't know exactly what they are).

This is a long-standing myth. I worked on Wall Street and have friends 
who have been doing it for years. Everybody uses double.

Andrei