Walter Bright wrote:
dsimcha wrote:
I assume, when referring to the ones that do throw, you mean functions
written in
C++ or D, but declared w/ C linkage. If so, you could make this a
per-module
setting that defaults to not assuming nothrow. For example, let's say
you made
this pragma(Linkage, nothrow). Then, if this statement is seen at the
top of a
module, everything declared with extern(Linkage) in that module is
assumed to be
nothrow. For standard C, Windows and POSIX API functions and for any
library
written in pure C, I believe (correct me if I'm wrong) this would be a
safe
assumption. At any rate, it would make nothrow a heck of a lot more
usable.
This will do it:
nothrow:
... rest of module ...
Isn't errno defined in some implementations to be thread-local?
Yes, but thread local doesn't mean pure.
If so, I guess we
still have a problem. Then again, in the long run it probably makes
sense to
reimplement a lot of the math stuff that still uses the C std lib in
pure D anyhow
so that things like CTFE work on it, but in the sort run I'm sure
that's not
anyone's top priority.
Don has already reimplemented most of them in D, this was done to:
1. ensure a minimum level of performance and accuracy; some C ones are
crappily done
2. properly support all the D floating point types and overloading rules
3. support NAN and INFINITY correctly
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.
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.
