convert mpf t to double with rounding-modes defined by ieee754

[usenett@gmx.de]

>> I tested my computation throughout with GMP and as well with MPFR. Working
>> with a large accumulator (in my case a variable with precision of 4288
>> bits), in which perhaps only some few limbs are used, the mpfr-version is
>> about a factor of 4-5 slower. That has neither anything to do, that the mpfr
>> authors are 'some random web/VB code monkeys', nor that 'C++ is slow'. The
>> mpfr-library just doesn't fit to my  problem. The way some things are
>> realized in gmp seem to be more profitable to me (just in my case, not
>> generally).

PP>  Which functions did you use?
PP>  What do you mean by "MPFR doesn't fit my problem"?
 
PP>  In my own benchs, MPFR is as fast as MPF. It evens beat MPF in some.

I generate three mpf(r)_t variables, do some 'random' operations on them and
read out the interval time counter of my Itanium2. Then I compare the average
computation time for the three blocks: initializations, set doubles and the
multiplications/additions.

The initialization is quite identically fast (about 727 clocks), the setting
of the double-values is about 94 (mpfr) to 1059 (gmp) clocks and the
operations about 1430 to 5600.

In the attachment there is an extract of my sourcecode.

Greets, Heinz