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Posted by Malcolm Dew-Jones on 12/06/05 20:04
Andy Hassall (andy@andyh.co.uk) wrote:
: On Mon, 05 Dec 2005 19:41:25 +0000, Philip Ronan <invalid@invalid.invalid>
: wrote:
: >"Andy Hassall" wrote:
: >
: >> You appear to be working with monetary values from the names in your original
: >> post. You shouldn't use floating point numbers for money; use integers,
: >> multiplied up to the minor currency. So £1.50 = 150.
: >
: >There might be a good reason for using floats. For example, all your sales
: >tax calculations will be rounded down if you use integers.
: Then you can multiply up to the number of decimal places required by your tax
: authority and apply their rounding rules (up or down) - more deterministic than
: having small but unpredictable amounts of money being lost or gained due to
: non-exact float representations. Depending on how many decimals you pick, the
: 32-bit limits on integers (31 bits for signed) could then become a problem for
: large transactions or monthly/yearly totals.
(My understanding, feel free to argue.)
Computer double size floating point numbers can perform calculations on
integer _values_ with out integer value errors (exactly like integer
numbers do).
But the computer double can represent a much larger range of exact integer
values.
So to avoid 32-bit limits on integer numbers, scale the value to create an
integer value (just like you suggest), but store and manipulate that value
using doubles.
I guess the only issue would be to determine if any part of a caculation's
integer result went beyond the range of what could be represented exactly,
but I think that question also arises if you use plain integers anyway, so
I'm not sure this is an additional problem. E.g. if you multiply two
large integers using integer arithmentic then the resulting value may not
be correct and you don't get an error to warn you - at least that is what
I confirmed in one quick test using one C compiler to multiple two large
integers.
--
This programmer available for rent.
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