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  ANSI Common Lisp   12 Numbers   12.2 Dictionary of Numbers

12.2.5 short-float, single-float, double-float, long-float Type

Supertypes:
short-float: short-float, float, real, number, t

single-float: single-float, float, real, number, t

double-float: double-float, float, real, number, t

long-float: long-float, float, real, number, t

Description:
For the four defined subtypes of type float, it is true that intermediate between the type short-float and the type long-float are the type single-float and the type double-float. The precise definition of these categories is implementation-defined. The precision (measured in "bits", computed as plog2b) and the exponent size (also measured in "bits," computed as log2(n+1), where n is the maximum exponent value) is recommended to be at least as great as the values in the next figure. Each of the defined subtypes of type float might or might not have a minus zero.

Recommended Minimum Floating-Point Precision and Exponent Size
Format Minimum Precision Minimum Exponent Size
Short 13 bits 5 bits
Single 24 bits 8 bits
Double 50 bits 8 bits
Long 50 bits 8 bits

There can be fewer than four internal representations for floats. If there are fewer distinct representations, the following rules apply:

Compound Type Specifier Kind:
Abbreviating.

Compound Type Specifier Syntax:
(short-float [short-lower-limit [short-upper-limit]]) (single-float [single-lower-limit [single-upper-limit]]) (double-float [double-lower-limit [double-upper-limit]]) (long-float [long-lower-limit [long-upper-limit]])

Compound Type Specifier Arguments:
short-lower-limit, short-upper-limit - interval designators for type short-float. The defaults for each of lower-limit and upper-limit is the symbol *.

single-lower-limit, single-upper-limit - interval designators for type single-float. The defaults for each of lower-limit and upper-limit is the symbol *.

double-lower-limit, double-upper-limit - interval designators for type double-float. The defaults for each of lower-limit and upper-limit is the symbol *.

long-lower-limit, long-upper-limit - interval designators for type long-float. The defaults for each of lower-limit and upper-limit is the symbol *.

Compound Type Specifier Description:
Each of these denotes the set of floats of the indicated type that are on the interval specified by the interval designators.

Allegro CL Implementation Details:
None.

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