
ANSI Common Lisp 12 Numbers 12.2 Dictionary of Numbers
12.2.4 float 
System Class 
 Class Precedence List:

float,
real,
number,
t
 Description:

A float
is a mathematical rational (but not a Common Lisp rational)
of the form
s f b^{ep},
where s is +1 or 1, the sign;
b is an integer
greater than 1, the base or radix of the representation;
p is a positive integer,
the precision (in baseb digits) of the float;
f is a positive integer
between b^{p1} and
b^{p}1 (inclusive), the significand;
and e is an integer, the exponent.
The value of p and the range of e
depends on the implementation and on the type of float
within that implementation. In addition, there is a floatingpoint zero;
depending on the implementation, there can also be a "minus zero". If there
is no minus zero, then 0.0 and 0.0 are both interpreted as simply a
floatingpoint zero.
(= 0.0 0.0) is always true.
If there is a minus zero, (eql 0.0 0.0) is false,
otherwise it is true.
The types shortfloat, singlefloat, doublefloat,
and longfloat are subtypes of type float. Any two of them must be
either disjoint types or the same type;
if the same type, then any other types between them in the
above ordering must also be the same type. For example,
if the type singlefloat and the type longfloat are the same type,
then the type doublefloat must be the same type also.
 Compound Type Specifier Kind:

Abbreviating.
 Compound Type Specifier Syntax:

(float [lowerlimit [upperlimit)]]
 Compound Type Specifier Arguments:

lowerlimit, upperlimit  interval designators
for type float.
The defaults for each of lowerlimit and upperlimit is the symbol *.
 Compound Type Specifier Description:

This denotes the floats on the interval described by
lowerlimit and upperlimit.
 See Also:

Figure 2.3.1 Numbers as Tokens,
Section 2.3.2 Constructing Numbers from Tokens,
Section 22.1.3.1.3 Printing Floats
 Notes:

Note that all mathematical integers are representable not only as
Common Lisp reals, but also as complex floats. For example,
possible representations of the mathematical number 1
include the integer 1,
the float 1.0,
or the complex #C(1.0 0.0).
 Allegro CL Implementation Details:

None.
