doubling your bits

["David L. Andre" <DLA@diamond.s4cc.symbolics.com>]

    Date: Wed, 25 Nov 87 10:58 EST
    From: Bill Long <WJL@ZERMATT.LCS.MIT.EDU>


	    I was wondering...
	    1) How much slower would coerce be if it added decimal zeros?
	     eg., (coerce .1 'double-float) -> 0.1d0

	It would be wrong.

    It depends what you would like to mean by .1.  I understand that when
    you type .1s0, the number you are really stuck with is
    0.10000000149011619... so one possible interpretation of coerce (and I
    take it, the IEEE sanctioned one) is to add more bits of that number.
    That way, (loop for n from 1 to 1000000 sum (coerce .1 'double-float))
    will still give 100958.34.  However, if what you really meant by .1 is
    decimal .1, the number .1s0 is an approximation and the 958.34 is round
    off 1error0.  I agree with James A. Reith that what I want is
    (coerce .1 'double-1decimal0-float), but it doesn't exist.

James A. Reith is wrong as well.  I don't have time to educate either of
you on this.  Perhaps somebody with more patience than I can try.

	    -Bill Long