[libmath-prime-util-perl] 13/50: Initial primes.pl implementation

[Partha P. Mukherjee]

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ppm-guest pushed a commit to annotated tag v0.13
in repository libmath-prime-util-perl.

commit 303c0444655ec29e6709f6c9b2d14268653879f2
Author: Dana Jacobsen <dana at acm.org>
Date:   Tue Oct 16 04:25:04 2012 -0600

    Initial primes.pl implementation
---
 bin/primes.pl | 97 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 97 insertions(+)

diff --git a/bin/primes.pl b/bin/primes.pl
new file mode 100755
index 0000000..0b97635
--- /dev/null
+++ b/bin/primes.pl
@@ -0,0 +1,97 @@
+#!/usr/bin/env perl
+use strict;
+use warnings;
+use Math::BigInt;
+use Getopt::Long;
+use Math::Prime::Util qw/primes next_prime is_prime/;
+$| = 1;
+
+my $show_safe = 0;
+my $show_sophie = 0;
+my $show_twin = 0;
+my $segment_size = 30 * 128_000;   # 128kB
+
+GetOptions( "safe"   => \$show_safe,
+            "sophie" => \$show_sophie,
+            "twin"   => \$show_twin,
+            "help"   => sub { die_usage() },
+          ) || die_usage();
+
+# Get the start and end values.  Verify they're positive integers.
+die_usage() unless @ARGV == 2;
+my ($start, $end) = @ARGV;
+die "$start isn't a positive integer" if $start =~ tr/0123456789//c;
+die "$end isn't a positive integer" if $end =~ tr/0123456789//c;
+
+# Turn start and end into bigints if they're very large
+if ( ($start >= ~0 && $start ne ~0) || ($end >= ~0 && $end ne ~0) ) {
+  $start = Math::BigInt->new($start);
+  $end = Math::BigInt->new($end);
+}
+
+while ($start <= $end) {
+
+    # small segment size if we're doing bigints
+    $segment_size = 10000 if $start > ~0;
+
+    my $seg_start = $start;
+    my $seg_end = $start + $segment_size;
+    $seg_end = $end if $end < $seg_end;
+    $start = $seg_end+1;
+
+    # Get a list of all primes in the segment.
+    my @p = @{primes($seg_start, $seg_end)};
+    #warn "-- ", scalar @p, " primes between $start and $segment_end\n";
+    next unless scalar @p > 0;
+
+
+    # Restrict to twin primes if requested.
+    if ($show_twin) {
+      # Add a last element so we can look at it.  Simple: push next_prime.
+      push @p, is_prime($p[-1]+2) ? $p[-1]+2 : 0;
+      # Trivial but slow:
+      #@p = grep { is_prime( $_+2 ); } @p;
+      # Loop over @p looking for values with prime == next+2
+      my @twin;
+      my $prime = shift @p;
+      foreach my $next (@p) {
+        push @twin, $prime if $prime+2 == $next;
+        $prime = $next;
+      }
+      @p = @twin;
+      #warn "   reduced to ", scalar @p, " twin primes\n";
+    }
+
+
+    # Restrict to safe primes if requested.
+    if ($show_safe) {
+      @p = grep { is_prime( ($_-1) >> 1 ); } @p;
+      #warn "   reduced to ", scalar @p, " safe primes\n";
+    }
+
+
+    # Restrict to Sophie Germain primes if requested.
+    if ($show_sophie) {
+      @p = grep { is_prime( 2*$_+1 ); } @p;
+      #warn "   reduced to ", scalar @p, " SG primes\n";
+    }
+
+    # print this segment
+    print join("\n", @p), "\n"  if scalar @p > 0;
+}
+
+sub die_usage {
+  die <<EOU;
+Usage: $0 [options]  START  END
+
+Displays all primes between the positive integers START and END, inclusive.
+
+Options:
+  --help      displays this help message
+  --safe      displays only safe primes, where (p-1)/2 is also prime
+  --twin      displays only twin primes, where p+2 is also prime
+  --sophie    displays only Sophie Germain primes, where 2p+1 is also prime
+
+Note that options can be combined, e.g. display all safe twin primes.
+EOU
+}

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