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*To*: barmar@think.com*Subject*: RE: X3T2 activities*From*: 12-Feb-1991 1017 <vanroggen@hancok.enet.dec.com>*Date*: Wed, 13 Feb 91 03:20:27 PST

As it so happens, X3T2, Language Compatible Arithmetic Standard, has already included a section on Common Lisp. One minor point was brought up: The definition of the xxx-EPSILON constants is not quite right. The problem is that if these values represent the smallest E such that (/= (+ 1 E) 1), then they will have to change according to the rounding mode if it's an IEEE implementation. However, I thought that any particular CL implementation could work around this by not implementing the xxx-EPSILON constants by the usual DEFCONSTANT mechanism. On the other hand, Common Lisp could change its definition of those constants to be the same as what LCAS specifies. It defines epsilon to be radix^(1-precision). This is the ratio of the weight of the least significant digit of the fraction radix^(-precision) to 1/radix. Another description is that epsilon is the largest relative representation error for all normalized values. Copies of ANSI document X3T2/91-006, LCAS V3.0, 26 Dec 1990, can probably be obtained (I haven't asked if they're able and willing) from Brian Wichmann, baw@seg.npl.co.uk, or Martha Jaffe, jaffe@rdvax.enet.dec.com. If they can't provide the file via the Internet, I'm willing to make hard copies. ---Walter

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