[pypy-dev] Contributing to pypy [especially numpy]
arigo at tunes.org
Sun Oct 16 23:21:34 CEST 2011
On Sun, Oct 16, 2011 at 19:13, David Cournapeau <cournape at 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.)
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