http://qs1969.pair.com?node_id=483469

Here's my take on it. Highlights: use Eratosthenes' sieve to determine a factor or primality for integers up to the max required; work out when an additional numerator or denominator kicks in (@switch), and pass over the numbers in reverse order, so each need be visited only once; build up two BigInts for numerator and denominator and just switch to BigFloats to divide the two at the end.

The single division at the end takes over 2/3 of the total time, so I'd expect using GMP or Pari for the maths would cut it greatly:

zen% perl t1 807060464786760409757687767524310994172947695099349876516088e-7089 sieve: 0 wallclock secs ( 0.09 usr + 0.02 sys = 0.11 CPU) build: 4 wallclock secs ( 4.38 usr + 0.00 sys = 4.38 CPU) divide: 9 wallclock secs ( 8.90 usr + 0.00 sys = 8.90 CPU) total: 13 wallclock secs (13.37 usr + 0.02 sys = 13.39 CPU) zen%

Things that made negligible difference: dropping accuracy to 40 (!); initialising my \$bii = Math::BigInt->new(\$i) before the multiply loops; the \$r->bsstr call.

I noticed that the numerator consists of 855 prime factors comprising 755 distinct primes; the denominator has 2308 of which 2306 are distinct. No surprise, then, that bpow() isn't a win.

Here's the code:

#!/usr/bin/perl -w use strict; use List::Util qw/ max /; use Math::BigInt; use Math::BigFloat; use Benchmark; my @num = ( 10389, 45700, 44289, 11800 ); my @den = ( 56089, 989, 9400, 43300, 2400 ); my(@fact, @freq, @switch); # sieve factors my \$t0 = new Benchmark; my \$max = max(@num, @den); for (my \$i = 2; \$i * \$i < \$max; ++\$i) { ++\$i while \$fact[\$i]; # skip to next prime for (my \$j = \$i * \$i; \$j < \$max; \$j += \$i) { \$fact[\$j] ||= \$i; } } ++\$switch[\$_] for @num; --\$switch[\$_] for @den; my \$t1 = new Benchmark; my \$count = 0; my \$num = Math::BigInt->new(1); my \$den = Math::BigInt->new(1); for my \$i (reverse 1 .. \$max) { no warnings qw/ uninitialized /; \$count += \$switch[\$i]; my \$f = \$count + \$freq[\$i]; if (\$fact[\$i]) { \$freq[\$fact[\$i]] += \$f; \$freq[\$i / \$fact[\$i]] += \$f; } elsif (\$f > 0) { \$num *= \$i for 1 .. \$f; } elsif (\$f < 0) { \$den *= \$i for \$f .. -1; } } my \$t2 = new Benchmark; Math::BigFloat->accuracy(60); my \$r = Math::BigFloat->new(\$num) / \$den; print \$r->bsstr, "\n"; my \$t3 = new Benchmark; time_delta("sieve", \$t1, \$t0); time_delta("build", \$t2, \$t1); time_delta("divide", \$t3, \$t2); time_delta("\ntotal", \$t3, \$t0); sub time_delta { print +shift, ": ", timestr(timediff(@_)), "\n"; }

Hugo