[Python-Dev] Nondeterministic long-to-float coercion

Bryan O'Sullivan bos at serpentine.com
Thu Oct 19 23:08:33 CEST 2006

Raymond Hettinger wrote:
> My colleague got an odd result today that is reproducible on his build
> of Python (RedHat's distribution of Py2.4.2) but not any other builds
> I've checked (including an Ubuntu Py2.4.2 built with a later version of
> GCC).  I hypothesized that this was a bug in the underlying GCC
> libraries, but the magnitude of the error is so large that that seems
> implausible.

These errors are due to a bit or two being flipped in either the long or 
double representation of the number.  They could be due to a compiler 
bug, but other potential culprits include bad memory, a bum power supply 
introducing noise, or cooling problems.

Has your colleague run memtest86 or other load tests for a day on their box?


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