floats

[RB]

I read somewhere awhile back (unless I am confused) that the
modern day math coprocessors did operations on 80bit
floating point values. If the input value was a smaller bit length
it was converted up and then converted back down after.
Is this true ?
And if so I would surmise that it is a trivial performance factor of
conversion so that using a float as oppose to a double ( if the
precision offered by a float was sufficient ) is advantageous only
in the amount of storage it requires ?

[James Harris]

For x86, yes, you are right. IIRC the maths coprocessor *can* be
changed to use floating point numbers less precise than 80-bit and
that's sometimes worth doing - such as for fast divides.

Check out instrucion timing tables documented by Agner Fog for lots of
details.

James

[RB]

Thanks James