GLS's change to Moon's floating-point extractors proposal

[David A. Moon <Moon at SCRC-TENEX at MIT-MC>]

    Date:  4 October 1982 2355-EDT (Monday)
    From: Guy.Steele at CMU-10A

    I support Moon's proposal, but would like to suggest that FLOAT-SIGN
    be modified to
	    (FLOAT-SIGN x &optional (y (float 1 x)))
	    returns z such that x and z have same sign and (= (abs y) (abs z)).
    In this way (FLOAT-SIGN x) returns 1.0 or -1.0 of the same format as x,
    and FLOAT-SIGN of two arguments is what the IEEE proposal calls COPYSIGN,
    a useful function indeed in numerical code.

This is the SIGNUM function, which already exists on page 125 of the Colander.
If my memory of the past 2 months' discussion is accurate, it was extended
to the 2-argument case; the Colander only allows one argument.

FLOAT-SIGN was intended to be something else, and would return 0 or 1 rather
than 1.0 or -1.0.  Perhaps FLOAT-SIGN is redundant given the existence of
SIGNUM.  There is only one problem with this, which I think I pointed out in
my message: the minus zero in the proposed IEEE standard.  I'm sure that
SIGNUM of this has to be -0.0 rather than -1.0 (although possibly it has
to be +0.0).  And MINUSP of -0.0 has to be NIL.  Furthermore the standard
specially specifies that (= -0.0 0.0) => T.  So if you're writing a portable
floating point number printer, you need some way to know to print a minus
sign for minus zero.  If EQ worked on numbers you could use it.