Paul D. Anderson wrote:
Don Wrote:
Paul D. Anderson wrote:
Does anyone have strong feelings for/against any of these options??
Paul
My opinion -- precision should be a per-object setting, since it is a
property of the data. Rounding etc is a property of the operators and
functions and should be thread-local, and set by creating a scope struct
with a constructor that sets the mode to a new value, and a destructor
which restores it to the previous one.
eg
BigFloat a = 5e50;
BigFloat b = 1e-20;
{
BigFloatRounding(ROUND_DOWN); // applies until end of scope
a*=sin(b);
}
// we're back in round-to-nearest.
I like that. I didn't consider scope as an option, but that's really what's
wanted now that you've pointed it out.
I agree that precision is part of the data, but it needs to be considered as
part of the operation as well. Multiplying two floats produces a number whose
potential precision is the sum of the operands' precision. We need a method to
determine what the precision of the product should be. Not that it's difficult
to come up with an answer -- but we have to agree on something. That's what the
context provides.
Yes, I guess you'd need to specify a maximum precision in the scope, as
well.
By the way, when I get around to adding rounding and exception control
for the FPU in std.math, I propose to do it in this way as well, by
default. The idea from C that the rounding mode can legally be changed
at any time is ridiculous.
Thanks for your input.
Paul
