bigfloat II

[Don]

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
> 
> 
>