Hi, This FBFS bug comes down to the POCL on i386 which is not able to perform calculation as described by the OpenCL spec.
It is likely a numerical optimization at the wrong place as those tests ensures the calculation are performed as expected. This is described in: https://en.wikipedia.org/wiki/Kahan_summation_algorithm#Possible_invalidation_by_compiler_optimization If I find some time I could have a look at it, but on the other hand, pyFAI does not support 32bits architecture as it requires often more than 2GB of memory for real scientific application. -- Jérôme Kieffer: core dev of pyFAI.