Hi, i'm using a 3rd-party engine http://glaros.dtc.umn.edu/gkhome/metis/metis/overview for partitioning some complex data. it worked fine for years until today (may 13)... observations: - the 32-bit metis build produces nice and balanced partitons. - the 64-bit metis build produces bad and unbalanced partitons. the metis' engine uses arrays of integers on the public interface and internally some float-based and unsafe in terms of precison (x<y and x==y) operations. so, i've built/tested following metis variants: 1). -m32 -march=pentium4 -O1 - works fine. 2). -m32 -march=pentium4 -O1 -mfpmath=sse - works fine. 3). -m64 -march=x86-64 -O1 - bad/unbalanced partitions. 4). -m64 -march=x86-64 -O1 -mfpmath=387 - bad/unbalanced partitions. at this point i've expected wrong results (< 80-bit precision) from variants 2/3 and good results from variants 1/4 but the real world differs. next, i've isolated a one place in sources with float x<y stmt and changed it to (x-y)<0.00001. with such change both native 1/3 variants give nice/equivalent results. so, where is the problem? is the variants 1/4 really equivalent? BR, PaweÅ.
