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

Raymond Hettinger rhettinger at ewtllc.com
Thu Oct 19 22:07:31 CEST 2006

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.  Does anyone have a clue what is going-on?  


Python 2.4.2 (#1, Mar 29 2006, 11:22:09) [GCC 4.0.2 20051125 (Red Hat
4.0.2-8)] on linux2 Type "help", "copyright", "credits" or "license" for
more information.
>>> set(-19400000000 * (1/100.0) for i in range(10000))
set([-194000000.0, -193995904.0, -193994880.0])

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