Re: fp, rounding, decimal arithmetic - definitive account?

Hey George, My point is: I'm not against improving accuracy of floating point arithmetic in PHP (although it could lead to some weird compatibility problems with older version) but I wouldn't advise people who really, really have to rely on their numbers to be correct to use floats anyway. George Whiffen wrote:

Exactly my point. When coding php you need floating point you can trust or it is useless. As I said, bc is probably the best currently

You can never trust floating point if you need both big numbers and precision at the same time. Floating point is always a trade off between the two.

If I'm wrong, and it's really only bc that can be trusted to add 0.1 and 0.1, then shouldn't we be using that internally, rather than pretending to have a useable fp decimal arithmetic?

Floating point (even the current PHP implementation) is fine if you're happy enough with approximations which is the case 99% of the time.

P.S. I'm interested that you have money numbers so big that 15 digits are not enough. It can't be gross world income which still isn't up

I store cent values as integer strings and I possibly have to deal with values bigger than 214 million bucks (where PHP starts to convert ints to float) so I decided to go for BC Math. I didn't even care to check what the range/precision limits of floats are as I wanted something absolutely predictable, no matter what numbers are put into the system by our customers. Just because you're paranoid doesn't mean they're not after you :-) - Chris