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 2017-12-10, 12:30 #1 axn     Jun 2003 2×5×479 Posts Pminus1 - Bug report and feature request The following is a bug in calc_exp Code:  if (len >= 50) { giant x; calc_exp (pm1data, k, b, n, c, g, B1, p, lower, lower + (len >> 1)); x = allocgiant (len); calc_exp (pm1data, k, b, n, c, x, B1, p, lower + (len >> 1), upper); mulg (x, g); free (x); return; } itog (2*n, g); for ( ; *p <= B1 && (unsigned long) g->sign < len; *p = sieve (pm1data->sieve_info)) { uint64_t val, max; val = *p; max = B1 / *p; while (val <= max) val *= *p; ullmulg (val, g); } g is initialized to 2*n. The problem is that, this is done for every (recursive) tail call of calc_exp, instead of just the first one, so we end up with B/50 (or more) multiples of 2*n. This just makes stage 0 longer than needed (probably on the order of 5% or so). What is needed: Code: if(lower==0) itog (2*n, g); else setone(g); Now, the feature request: Make stage 0 bigger. Right now it is a paltry 1M (stage_0_limit = (pm1data.B > 1000000) ? 1000000 : pm1data.B;), which is probably fine for regular GIMPS work, but at the mid-to-low end, we routinely deal with much bigger B1 So instead, make it as big as possible (100m is not too bad, since we're looking at < 20MB memory use). If calc_exp takes lot of time to do the actual calculation, make it as big as can be reasonably done by a modern processor in, say 60 seconds. Last fiddled with by axn on 2017-12-10 at 12:31