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gam3,
• Cache is now persistent
• Primeness is determined in C
• The 2 4 trick is used in checking near numbers also
• An iterator is used in lieu of a stack
#!/usr/bin/perl use strict; use warnings; use DBM::Deep; use Inline C =>; my \$prime = DBM::Deep->new( 'primes.db' ); #\$prime->{is}{\$_} = 1 for (2, 3, 5, 7, 11, 13, 17, 19, 23); # 1st run +only my \$next = find_near_primes(10000 => 100); while ( my \$p = \$next->() ) { print "\$p\n"; } sub find_near_primes { my (\$num, \$tot) = @_; my (\$below, \$above, \$up, \$down); my \$by_2_4 = sub { my \$n = shift; return sub { return \$n = \$n == 2 + ? 4 : 2 } }; my \$dir = -1; return sub { return () if ! \$tot--; \$dir *= -1; if ( \$num ) { \$num = \$num - \$num % 3; \$num += not (\$num % 2) ? -1 : 2; (\$below, \$above, \$num) = (\$num, \$num, undef); (\$up, \$down) = (\$by_2_4->( 4 ), \$by_2_4->( 2 )); \$below -= \$down->(); } if ( \$dir == 1 || \$below < 5 ) { if ( ! \$prime->{is}{\$above} ) { \$above += \$up->() while \$prime->{not}{\$above}; while ( ! is_prime( \$above ) ) { \$prime->{not}{\$above} = 1; \$above += \$up->() while \$prime->{not}{\$above}; last if \$prime->{is}{\$above}; } \$prime->{is}{\$above} = 1; } my \$p = \$above; \$above += \$up->() and return \$p; } else { if ( ! \$prime->{is}{\$below} ) { \$below -= \$down->() while \$prime->{not}{\$below}; while ( ! is_prime( \$below ) ) { \$prime->{not}{\$below} = 1; \$below -= \$down->() while \$prime->{not}{\$below}; last if \$prime->{is}{\$below}; } \$prime->{is}{\$below} = 1; } my \$p = \$below; \$below -= \$down->() and return \$p; } }; } __END__ __C__ #include <math.h> short is_prime (unsigned long num) { unsigned long i = 5; unsigned long j = sqrt( num ); while ( i <= j ) { if ( num % i == 0 ) return 0; i += 2; if ( num % i == 0 ) return 0; i += 4; } return 1; }
Tag - you're it!

Cheers - L~R

In reply to Re^3: a close prime number by Limbic~Region
in thread a close prime number by Anonymous Monk

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