Lisp Knowledgebase
Title: LispWorks 5 default floating point type is different from LispWorks 4
ID: 17048
| Product: LispWorks Version: 5 OS: All | |
| Description: When porting code to LispWorks 5 from LispWorks 4 on Windows or Linux, be aware that the default floating point format has changed. LispWorks 5 supports the following distinct floating point types on all platforms: short-float (same range as IEEE single precision but with fewer mantissa bits) single-float (IEEE single precision) double-float (IEEE double precision) LispWorks 4 supports only one distinct floating point type on Windows and Linux: double-float (IEEE double precision) All other float types are equivalent to double-float. This affects the following situations. 1. The default floating point format when reading numbers using the E exponent marker (or with no exponent marker) is controlled by the variable cl:*read-default-float-format* which defaults to single-float. In LispWorks 5 this makes a single-float, whereas in LispWorks 4 on Windows and Linux this makes a double-float. Example: In LispWorks 4 on Windows *read-default-float-format* is double-float, so: (truncate 3E10) => 30000000000 In LispWorks 5 *read-default-float-format* is single-float, which cannot represent 30000000000 accurately, so the value is rounded: (truncate 3E10) => 30000001024 If you force the value to be a double-float, then truncate works correctly, for example: (truncate 3D10) => 30000000000 2. When calling the function float with 1 rational argument, LispWorks 5 always returns a single-float. In LispWorks 4 on Windows and Linux it returns a double-float. | |
| See Also: Workaround: Set cl:*read-default-float-format* to double-float or change the code to use the D exponent marker. Patch: | |
| Hardware:N/A | |
| Summary: | |
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| Reported: | |