Don wrote:
tango.math doesn't use the C library at all, except when inline asm is
unavailable. Of they differ from the C functions, in that none of them
set errno!
One really annoying issue still remains, though -- the floating point
flags in the CPU. They are entirely deterministic, but are they
considered to be part of the return value of the function? Or would we
allow them to be ignored?
A compiler could check the exception flags before allowing memoisation.
But one could also do the same thing for 'errno'.
Likewise, floating point rounding modes. Essentially, the floating point
status register is a hidden global variable, read from# and written to
during every floating point operation.
# - only the rounding mode and truncation affect the return value. We
could deal with it by regarding that as a whole-program setting. But
(depending on the CPU), the old exception flags generally get ORed with
the new exception flags.
Those are good points. I don't know what the answer is. My inclination
is to say if your program relies on changing the rounding mode or
fiddles with the exception flags, it's undefined behavior.
Also, you can set the flags to allow any floating point function to
throw a hardware exception. It's difficult for any function using
floating point to claim to be nothrow under ANY circumstances; but
that's a horrible limitation.
I would say that is not supported by D. I've never heard of a use for them.
