on floating-point numbers

[Grant Edwards]

On 2021-09-02, Hope Rouselle <hrouselle at jevedi.com> wrote:

> Suppose these numbers are prices in dollar, never going beyond cents.
> Would it be safe to multiply each one of them by 100 and therefore work
> with cents only?

The _practical_ answer is that no, it's not safe to use floating point
when doing normal bookeeping type stuff with money. At least not if
you want everything to balance correctly at the end of the day (week,
month, quarter, year or etc.). Use integer cents, or mills or
whatever. If you have to use floating point to calculate a payment or
credit/debit amount, always round or truncate the result back to an
integer value in your chosen units before actually using that amount
for anything.

In theory, decimal floating point should be usable, but I've never
personally worked with it. Back in the day (1980's) microcomputers
didn't have floating point hardware, and many compilers allowed you to
choose between base-2 floating point and base-10 (BCD) floating
point. The idea was that if you were doing financial stuff, you could
use BCD floating point.

--
Grant