[xacml] SH02: Use of decimal math should be justified

[Steve Hanna <steve.hanna@sun.com>]

It is unusual to specify the use of decimal math in
a specification like XACML, especially requiring strict
conformance to a detailed specification of decimal
math behavior. Many platforms do not support decimal
math. Binary math is much more common.

I can see why you might want to use decimal math for
this specification. Maybe you're likely to be doing a
lot of financial calculations. Still, I think it's a
bit odd that you require support for exponents, NaNs,
and the like in the implementation but don't provide
any way for a user to access these features. A simpler
approach would have been to leave the arithmetic
loosely specified, like XQuery has done.

At the least, I think you should add a few sentences
to the end of section A.12 Arithmetic evaluation saying

  Decimal arithmetic is used in order to provide
  results that closely match those expected by the
  average user.

Thanks,

Steve Hanna
Sun Microsystems, Inc.