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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 be-p,
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 base-b digits) of the float;
f is a positive integer
between bp-1 and
bp-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 floating-point 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
floating-point 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 short-float, single-float, double-float,
and long-float 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 single-float and the type long-float are the same type,
then the type double-float must be the same type also.
- Compound Type Specifier Kind:
-
Abbreviating.
- Compound Type Specifier Syntax:
-
(float [lower-limit [upper-limit)]]
- Compound Type Specifier Arguments:
-
lower-limit, upper-limit - interval designators
for type float.
The defaults for each of lower-limit and upper-limit is the symbol *.
- Compound Type Specifier Description:
-
This denotes the floats on the interval described by
lower-limit and upper-limit.
- 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.
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