Quote from: Enochian on June 09, 2011, 05:51:50 PM

I have no problem with requiring new code to be fixed point.

Great!

Quote from: Enochian on June 09, 2011, 05:51:50 PM

I am simply pointing out that removing existing floating point code isn't an emergency, that floating point arithmetic is exact when integers having less bits than the mantissa are involved, that panic over imagined precision or rounding issues when using floats for financial software is overblown, and that several Very High Level Languages popular for financial and actuarial work use floats internally, as does COBOL when performance is maximized.

It's exact for additions and subtractions (of values that were never divided).

If you divide one value by another, and now you add the result multiple times, you will likely obtain different results than if you had used fixed-point arithmetic (unless it was an exact division).

This can lead to results that are unexpected. It may also lead to different results depending on how the compiler optimized your code (e.g. whether it used SSE2 or the FPU), the architecture you're using, etc.

Quote from: Enochian on June 09, 2011, 05:51:50 PM

People seem to have the idea that all float operations involve some sort of random fuzziness which causes monetary calculations to drift from their actual values the more floating operations are performed. In reality, floats represent exact values on the real number line, and the result of a floating operation is the nearest machine number to the value that would have resulted had the operation been performed to infinite precision if one exists, and a value systematically chosen with zero bias if the exact value lies halfway between two machine numbers.

It's not as obvious and simple as you seem to imply, as I just proved to you.

The code is also non-portable because the 'double' type in C++ is not required to have 64 bits, in fact it can have only 32 bits which is obviously not enough to represent all bitcoin values (not even close).
The size of double does not only depend on the architecture and compiler that you are using, but also on the compilation flags.
The double type is only required to not be smaller than float.