Walter Bright wrote:
Don wrote:
Don wrote:
Walter Bright wrote:
Don wrote:
That's true, but if you're in a floatingpoint module, and you call
a non-floatingpoint module, it's your responsibility to make sure
that the rounding mode is back to normal. You're saying that you
don't care about the status flags. So it's your own fault if you
get surprising results.
The primary use for adjusting the rounding mode is for things like
implementing interval arithmetic. Thus, it's only ever used for
small functions.
Perhaps we can go with something simpler. If you call a pure
function, then the modes must be set to their defaults.
But then nothing in std.math can be pure.
My proposal is pretty simple -- I doubt we can come up with anything
simpler that's useful.
To clarify the effect of my proposal:
normal function calls floatingpoint function -- rounding mode
respected, sticky status flags can be ignored.
floatingpoint function calls floatingpoint function -- rounding mode
respected, sticky flags set correctly.
floatingpoint function calls normal function -- rounding mode may be
respected, or you may get default rounding instead (implementation
defined). Sticky flags may not be set in all cases, but none will be
cleared.
So, a floatingpoint function should not make any calls to normal
functions under circumstances in which it needs guaranteed rounding,
or where it relies on the sticky flags. I think that's a managable
limitation.
The only other alternative I can see is to require that EVERY function
save the status flags and check the control register before caching
any pure function. Which seems a lot of complexity for the sake of a
few really obscure cases.
I'm still not seeing the difference between this and saying that for
pure functions, the default modes are used. All the std.math functions
will be pure. How is this different from floatingpoint functions calling
normal functions?
The math functions need to work for any rounding mode, not just the
default mode. They also set the status flags correctly. In fact, they
are almost the only functions where this matters!
