Daniel Keep wrote:
Rainer Deyke wrote:
Bill Baxter wrote:
Note that D already has things like !>. But quoth the spec:
"For floating point comparison operators, (a !op b) is *NOT* the same
as !(a op b)."
[emphasis added]
I had to check the spec for the difference. 'a !< b' and '!(a < b)'
/are/ equivalent in the sense that '(a !< b) == !(a < b)' for any values
of 'a' and 'b'. The vast majority of the time, the expressions 'a !< b'
and '!(a < b)' /are/ interchangeable. The difference is that '!(a < b)'
sets a global exception state if either operand is NaN, while 'a !< b'
does not.
This is, in my opinion, a significant design error in the language. The
difference between '!(a < b)' and 'a !< b' is not obvious. There is
nothing about the operator '<' that suggests that it should set a global
exception state, and there is nothing about '!<' that suggests that it
should /not/ set a global exception state. (Is global state for error
reporting ever a good idea in a high-level language?) It also adds
awkward expressions to the language, not just in the form '!(a < b)',
but in the form '!(a !< b)'.
I believe this is, or is the result of, an aspect of IEEE floating point.
-- Daniel
Yes. It's the hardware. It's hard to find situations where the
difference matters. And this is why !<> and !<>= are the only ones of
those operators which are actually useful.
