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.
