Hi guys, I was thinking that we could probably improve the confidence we have in double-checked results if we adopted the following tactic. Normally we run with the FPU set to round to nearest or even (the default mode). Suppose we ran first tests with rounding set to round down (towards -infinity) and double checks with rounding set to round up (towards +infinity). This would lose us about 1 bit precision in the mantissa, but, if a double check run verified the residual, we'd be _certain_ that rounding errors weren't compromising the algorithm. We would probably have to reduce the FFT size changeover points slightly to accomodate the small loss of precision, but would probably be able to regain the resulting throughput loss by reducing the frequency with which other "sanity checks" were done. The combination of round up/round down matching and randomized offset would surely lead to results obtained using the same program to be less likely to match incorrectly. Not that this is a particular problem, but we might be able to get the improvement for a very small (or possibly even negative) cost in execution time. Regards Brian Beesley _________________________________________________________________________ Unsubscribe & list info -- http://www.scruz.net/~luke/signup.htm Mersenne Prime FAQ -- http://www.exu.ilstu.edu/mersenne/faq-mers.txt
