Thorkil Naur
Using nhc98-1.16 to experiment with some number-theoretic computations (c.f. H. W. Lenstra: "Factoring integers with elliptic curves", Annals of Math., 126 (1987), 649-673), I ran into a "Segmentation fault" and also examples of inconsistent Integer computations. The result of executing the same program varies with the size of the heap (the +RTS -H<size> option).
I suspect that the fault here is in nhc98's runtime system. Your program deals with some very large integers, which are represented internally as variable-length arrays of machine words. The RTS checks whether sufficient continuous memory is available to represent the result of a calculation before doing it. I think probably the check is estimating the result size wrongly. As a consequence, when the heap is small, it will be more likely that the actual result overwrites the end of the heap, causing memory corruption that could lead to either a seg fault or incorrect computation.
I would be most grateful to receive some advice on how to proceed in this matter.
Until I get the opportunity to find and fix this bug properly, the simple workaround is to ensure that your programs always use a sufficiently large heap. You can set the default heapsize at compile-time if you wish, e.g. nhc98 -o prog prog.hs -H16M or hmake -nhc98 prog +CTS -H16M -CTS Regards, Malcolm