correctly-rounded base conversion

[David Keaton]

     If perfect floating point conversions are available without
losing any speed, they should be used.  However, in cases where there
is a tradeoff between speed and perfect conversions, I am not
convinced by the network computing argument.  IEEE and non-IEEE
machines represent different sets of numbers, so printing them out
perfectly does not solve the portability problem.  Even if everyone
does perfect conversions, shipping the same number from Cray -> Sun ->
Cray is likely to yield a number that is different from what it
started out to be.