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ppm-guest pushed a commit to annotated tag v0.32
in repository libmath-prime-util-perl.

commit 25809f6a058a7d1a578b922018757bc81dbb359d
Author: Dana Jacobsen <d...@acm.org>
Date:   Fri Aug 16 18:28:33 2013 -0700

    Update a couple examples
---
 examples/sophie_germain.pl | 38 +++++++++++++++++++++++++++-----------
 examples/twin_primes.pl    | 29 +++++++++++++++++++++++------
 2 files changed, 50 insertions(+), 17 deletions(-)

diff --git a/examples/sophie_germain.pl b/examples/sophie_germain.pl
index 4588c7f..38c2f64 100755
--- a/examples/sophie_germain.pl
+++ b/examples/sophie_germain.pl
@@ -2,7 +2,9 @@
 use strict;
 use warnings;
 
-use Math::Prime::Util qw/-nobigint next_prime is_prime prime_iterator/;
+use Math::Prime::Util qw/-nobigint
+                         prime_iterator is_prime
+                         next_prime nth_prime_upper prime_precalc forprimes/;
 
 my $count = shift || 20;
 
@@ -11,7 +13,22 @@ my $count = shift || 20;
 # In this method, we add a filter in front of our iterator, to create a
 # Sophie-Germain-prime iterator.  This isn't the fastest way, but it's still
 # 20x faster than Math::NumSeq::SophieGermainPrimes at 300k.  If we add the
-# two-line precalc shown below, we can get another 4x or so more.
+# two-line precalc shown below, we can get another 4x or more.
+#
+# Example:
+#  time perl examples/sophie_germain.pl 300000 | md5sum
+#    d380d31256cc9bc54eb5f236b3edc16d  -
+#    9.673s
+#
+#  time perl -MMath::NumSeq::SophieGermainPrimes -E 'my $seq = 
Math::NumSeq::SophieGermainPrimes->new; do { say 0+($seq->next)[1] } for 
1..300000' | md5sum
+#    d380d31256cc9bc54eb5f236b3edc16d  -
+#    4m11.5s
+#
+# With method 2:
+#  time perl examples/sophie_germain.pl 300000 | md5sum
+#    d380d31256cc9bc54eb5f236b3edc16d  -
+#    1.828s
+
 
 sub get_sophie_germain_iterator {
   my $p = shift || 2;
@@ -26,18 +43,17 @@ for (1..$count) {
   print $sgit->(), "\n";
 }
 
-
 # Method 2.  At 300k this is 70x faster than Math::NumSeq::SophieGermainPrimes.
 #
-# my $estimate = 100 + int( nth_prime_upper($count) * 1.6 * log($count) );
-# prime_precalc(2 * $estimate);
+#my $estimate = 100 + int( nth_prime_upper($count) * 1.6 * log($count) );
+#prime_precalc(2 * $estimate);
 # 
-# my $prime = 2;
-# for (1..$count) {
-#   $prime = next_prime($prime) while (!is_prime(2*$prime+1));
-#   print "$prime\n";
-#   $prime = next_prime($prime);
-# }
+#my $prime = 2;
+#for (1..$count) {
+#  $prime = next_prime($prime) while (!is_prime(2*$prime+1));
+#  print "$prime\n";
+#  $prime = next_prime($prime);
+#}
 
 # Alternate method, 10-20% faster, would benefit from a tighter estimate.
 #
diff --git a/examples/twin_primes.pl b/examples/twin_primes.pl
index 91e5372..ac903f1 100755
--- a/examples/twin_primes.pl
+++ b/examples/twin_primes.pl
@@ -2,22 +2,25 @@
 use strict;
 use warnings;
 
-use Math::Prime::Util qw/prime_iterator nth_prime_upper prime_precalc/;
+use Math::Prime::Util qw/-nobigint
+                         prime_iterator next_prime
+                         nth_prime_upper prime_precalc/;
 
 my $count = shift || 20;
 
 # Find twin primes (numbers where p and p+2 are prime)
 
 # Time for the first 300k:
-#   3m28s  Math::NumSeq::TwinPrimes
-#   2.5s   this iterator
-#   9.1s   this iterator without the precalc
+#   3m36s  Math::NumSeq::TwinPrimes (Perl 5.19.2 with v61)
+#   1.4s   this iterator
+#   7.9s   this iterator without the precalc
 
 # This speeds things up, but isn't necessary.
 my $estimate = 5000 + int( nth_prime_upper($count) * 1.4 * log($count) );
 prime_precalc($estimate);
 
-sub get_twin_prime_iterator {
+# Create a twin prime iterator using the prime_iterator construct
+sub get_twin_prime_iterator1 {
   my $p = shift || 2;
   my $it = prime_iterator($p);
   my $prev = $it->();    # prev = 2
@@ -29,7 +32,21 @@ sub get_twin_prime_iterator {
     $prev;
   };
 }
-my $twinit = get_twin_prime_iterator();
+
+# Create a twin prime iterator using the next_prime function
+# A bit faster than the prime_iterator version.
+sub get_twin_prime_iterator2 {
+  my $start = shift || 2;
+  my $prev = next_prime($start-1);
+  my $p = next_prime($prev);
+  return sub {
+    do {
+      ($prev, $p) = ($p, next_prime($p))
+    } while ($p-$prev) != 2;
+    $prev;
+  };
+}
+my $twinit = get_twin_prime_iterator2();
 for (1..$count) {
   print $twinit->(), "\n";
 }

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