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cl:types:float [2017/05/01 21:00] (current)
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 +====== System Class FLOAT ======
 +
 +====Class Precedence List==== ​
 +**float**, **[[CL:​Types:​real]]**,​ **[[CL:​Types:​number]]**,​ **[[CL:​Types:​t]]**
 +
 +====Description====
 +
 +A //​[[CL:​Glossary:​float]]//​ is a mathematical rational (but __not__ a Common Lisp //​[[CL:​Glossary:​rational]]//​) of the form ''​s * f * b<​sup>​e - p</​sup>'',​ where ''​s''​ is ''​+1''​ or ''​-1'',​ the ''​sign'';​ ''​b''​ is an //​[[CL:​Glossary:​integer]]//​ greater than~1, the ''​base''​ or ''​radix''​ of the representation;​ ''​p''​ is a positive //​[[CL:​Glossary:​integer]]//,​ the ''​precision''​ (in base-''​b''​ digits) of the //​[[CL:​Glossary:​float]]//;​ ''​f''​ is a positive //​[[CL:​Glossary:​integer]]//​ between ''​b<​sup>​p - 1</​sup>''​ and ''​b<​sup>​p - 1</​sup>''​ (inclusive),​ the significand;​ and ''​e''​ is an //​[[CL:​Glossary:​integer]]//,​ the exponent. The value of ''​p''​ and the range of~''​e''​ depends on the implementation and on the type of //​[[CL:​Glossary:​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. **[[CL:​Functions:​(= 0.0 -0.0)]]** is always true. If there is a minus zero, **[[CL:​Functions:​(eql -0.0 0.0)]]** is //​[[CL:​Glossary:​false]]//,​ otherwise it is //​[[CL:​Glossary:​true]]//​.
 +
 +\reviewer{Barmar:​ What about IEEE NaNs and infinities?​}
 +
 +\reviewer{RWK:​ In the following, what is the "​ordering"?​ precision? range? Can there be additional subtypes of float or does "​others"​ in the list of four?}
 +
 +The //​[[CL:​Glossary:​type|types]]//​ **[[CL:​Types:​short-float]]**,​ **[[CL:​Types:​single-float]]**,​ **[[CL:​Types:​double-float]]**,​ and **[[CL:​Types:​long-float]]** are subtypes of **float**. Any two of them must be either //​[[CL:​Glossary:​disjoint]]//​ //​[[CL:​Glossary:​type|types]]//​ or the //​[[CL:​Glossary:​same]]//​ //​[[CL:​Glossary:​type]]//;​ if the //​[[CL:​Glossary:​same]]//​ //​[[CL:​Glossary:​type]]//,​ then any other //​[[CL:​Glossary:​type|types]]//​ between them in the above ordering must also be the //​[[CL:​Glossary:​same]]//​ //​[[CL:​Glossary:​type]]//​. For example, if the type **[[CL:​Types:​single-float]]** and the type **[[CL:​Types:​long-float]]** are the //​[[CL:​Glossary:​same]]//​ //​[[CL:​Glossary:​type]]//,​ then the type **[[CL:​Types:​double-float]]** must be the //​[[CL:​Glossary:​same]]//​ //​[[CL:​Glossary:​type]]//​ also.
 +
 +====Compound Type Specifier Kind====
 +Abbreviating.
 +
 +====Compound Type Specifier Syntax====
 +  * **float** [//​lower-limit//​ [//​upper-limit//​]]
 +
 +====Compound Type Specifier Arguments====
 +  * //​lower-limit//,​ //​upper-limit//​ - //​[[CL:​Glossary:​interval designator|interval designators]]//​ for //​[[CL:​Glossary:​type]]//​ **[[CL:​Types:​float]]**. The defaults for each of //​lower-limit//​ and //​upper-limit//​ is the //​[[CL:​Glossary:​symbol]]//​ **[[CL:​Types:​wildcard|*]]**.
 +  ​
 +====Compound Type Specifier Description====
 +This denotes the //​[[CL:​Glossary:​float|floats]]//​ on the interval described by //​lower-limit//​ and //​upper-limit//​. ​
 +
 +====See Also====
 +  * {\figref\SyntaxForNumericTokens}
 +  * {\secref\NumsFromTokens}
 +  * {\secref\PrintingFloats}
 +
 +====Notes====
 +Note that all mathematical integers are representable not only as Common Lisp //​[[CL:​Glossary:​real|reals]]//,​ but also as //​[[CL:​Glossary:​complex float|complex floats]]//. For example, possible representations of the mathematical number ''​1''​ include the //​[[CL:​Glossary:​integer]]//​ ''​1'',​ the //​[[CL:​Glossary:​float]]//​ ''​1.0'',​ or the //​[[CL:​Glossary:​complex]]//​ ''#​C(1.0 0.0)''​.
 +
 +\issue{REAL-NUMBER-TYPE:​X3J13-MAR-89}