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*To*: Steele%Tartan@CMU-CS-C.ARPA*Subject*: single-float-epsilon*From*: "David A. Moon" <Moon%SCRC-TENEX@MIT-MC.ARPA>*Date*: Wed, 28 Dec 83 00:48 EST*Cc*: Common-Lisp@SU-AI.ARPA

This message supersedes previous copies; please forgive the duplication. Sorry I didn't notice this before, but I'm not sure that the definition of single-float-epsilon given in the manual is really what you intended. Specifically, on most machines (those that do rounding to nearest) this number is -not- a power of 2, rather it is one unit in the least significant place more than a power of 2. I would think that most applications of this would prefer to have a power of 2. Is it possible that the definition you wanted was "the largest positive floating-point number e such that the expression (= (float 1 e) (+ (float 1 e) e)) is false when actually evaluated."? In the meantime I've fixed our implementation to conform to the manual instead of having a value that was off by a factor of a hair less than 2 (the person computing the value clearly must have assumed that it was meant to be a power of 2 and didn't consider other numbers).

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