On Sat, 15 Dec 2018 01:24:18 -0800
Darren Duncan <dar...@darrenduncan.net> wrote:
> If yours is a financial application then you should be using exact
> numeric types only
Color me skeptical. That very much depends on the application. IEEE
double-precision floating point is accurate to within 15 decimal
digits. The example given,
> 211496.26
gives, safely, a margin of 6 order of magnitude. If the application is
taking sums of 100's of thousands of dollars, it will stay accurate to
within a penny using floating point until there are millions of
entries:
10^15 รท 10^8 = 10^7
I doubt the financial application exists that sums milliions of entries
AND cares about the last penny.
I've seen advice about using integer arithmetic and implied decimal
points in textbooks. It's convenient in languages like Cobol, that
support it. In languages like C, floating point is too convenient --
and accurate -- to ignore.
I'm sure banks have regulations and approved rounding algorithms.
In decades of programming on Wall Street, though, we used floating
point for everything. The only problems I remember involved matching
results between systems when porting: the differences were
insignificant, but because they were visible they had to be explained.
That always took some work.
--jkl
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