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# Re: Fourth Draft "Unsafe fp optimizations" project description.

*To*: ejr at cs dot berkeley dot edu
*Subject*: Re: Fourth Draft "Unsafe fp optimizations" project description.
*From*: Brad Lucier <lucier at math dot purdue dot edu>
*Date*: Mon, 13 Aug 2001 11:32:25 -0500 (EST)
*Cc*: lucier at math dot purdue dot edu (Brad Lucier), gcc at gcc dot gnu dot org

Re:
*) Note that -0.0 == 0.0, so -A+B == B-A is always true
for numerical A and B. Obviously, NaNs will make it
always unordered.
It is true that -0.0 is numerically equal to 0.0, but it not (Lisp)
equivalent, in that 1.0/(0.0) is most definitely not (numerically equal ||
equivalent || or identical) to 1.0/(-0.0). (I
would define Lisp equivalency as being able to substitute two values
in any expression and get the same answer; real Lispers can yell at me
now, and I'll fall back to Scheme ;-) If this note refers to our previous
discussion of whether -A+B -> B-A is a valid transformation, I think
we were using "same" in the sense "equivalent".
Brad Lucier