On Sun, Oct 16, 2011 at 5:21 PM, Armin Rigo <ar...@tunes.org> wrote: > Hi David, > > On Sun, Oct 16, 2011 at 19:13, David Cournapeau <courn...@gmail.com> > wrote: > > (...) and there is also the issue > > of correctness in floating point code generation. Given that > > decade-old compilers get it wrong, I would expect pypy jit to have > > quite a few funky corner cases as well. > > No, we should not have corner cases, because we don't go there at all. > We know very well that rewriting operations on floats can slightly > change their results, so we don't do it. In other words the JIT > produces a sequence of residual operations that has bit-wise the same > effect as the original sequence of Python operations. > > (More precisely, it seems that we only replace FLOAT_MUL(x, 1.0) by > "x" and FLOAT_MUL(x, -1.0) by "-x", as well as simplify repeated > FLOAT_NEG's and assume that FLOAT_MUL's are commutative. As far as I > can tell these trivial optimizations are all bit-wise correct, at > least on modern FPUs.) > > > A bientôt, > > Armin. > _______________________________________________ > pypy-dev mailing list > pypy-dev@python.org > http://mail.python.org/mailman/listinfo/pypy-dev >
I should note that I wrote all of these operations by verifying that GCC would do them, as well as testing on obscure values. Note for example that we don't constant fold x + 0.0 (changes the sign of x at x== -0.0). ALex -- "I disapprove of what you say, but I will defend to the death your right to say it." -- Evelyn Beatrice Hall (summarizing Voltaire) "The people's good is the highest law." -- Cicero
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