Re: expand and truncate and 387

[Stephen L Moshier <moshier at mediaone dot net>]

> Don't the other control settings simply limit the maximum precision available?

The purpose of the precision controls is to invoke strict rounding
rules for each mode.  If you wanted to get mostly the same answers
from x86 as from a real IEEE machine, you would use the precision settings.

> The single precision setting is not recommended, presumably since it
> eliminates double, so there is no point in making conversions work under it.

This sounds like you were hypnotized by Intel spin-doctor propaganda!
On an 8087 or 80287 chip you would not want to use the single
precision setting, no.  The major bugs were fixed in later models.


> This leaves conversion from single (float) to double, and doesn't that work
> the same regardless of whether the control setting is double or long double?

That may be true in one sense, but you might still have to execute an
instruction if you wanted the IEEE flags to be set properly.