[libmath-prime-util-perl] 24/35: Update with some more iterator examples

[Partha P. Mukherjee]

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ppm-guest pushed a commit to annotated tag v0.33
in repository libmath-prime-util-perl.

commit ec94f133d3efb393b33c19ceb7cf61b752b57ad5
Author: Dana Jacobsen <dana at acm.org>
Date:   Mon Nov 11 14:10:59 2013 -0800

    Update with some more iterator examples
---
 examples/twin_primes.pl | 41 ++++++++++++++++++++++++++++++++++-------
 1 file changed, 34 insertions(+), 7 deletions(-)

diff --git a/examples/twin_primes.pl b/examples/twin_primes.pl
index ac903f1..362a737 100755
--- a/examples/twin_primes.pl
+++ b/examples/twin_primes.pl
@@ -3,17 +3,25 @@ use strict;
 use warnings;
 
 use Math::Prime::Util qw/-nobigint
-                         prime_iterator next_prime
-                         nth_prime_upper prime_precalc/;
+                         prime_iterator  prime_iterator_object
+                         next_prime  is_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:
-#   3m36s  Math::NumSeq::TwinPrimes (Perl 5.19.2 with v61)
-#   1.4s   this iterator
-#   7.9s   this iterator without the precalc
+#   1.0s   bin/primes.pl --twin 2 64764839
+#   1.4s   get_twin_prime_iterator2
+#   2.3s   get_twin_prime_iterator1
+#   4.1s   get_twin_prime_iterator3
+#   6.1s   get_twin_prime_iterator3 (object iterator)
+#   7.6s   get_twin_prime_iterator2 without precalc
+#   8.4s   get_twin_prime_iterator1 without precalc
+#  10.9s   get_twin_prime_iterator3 without precalc
+#  13.1s   get_twin_prime_iterator3 without precalc (object iterator)
+# 219.8s   Math::NumSeq::TwinPrimes (Perl 5.19.4 with v66)
 
 # This speeds things up, but isn't necessary.
 my $estimate = 5000 + int( nth_prime_upper($count) * 1.4 * log($count) );
@@ -37,8 +45,8 @@ sub get_twin_prime_iterator1 {
 # 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);
+  my $p = next_prime($start-1);
+  my $prev = next_prime($p);
   return sub {
     do {
       ($prev, $p) = ($p, next_prime($p))
@@ -46,6 +54,25 @@ sub get_twin_prime_iterator2 {
     $prev;
   };
 }
+
+# Use Iterator::Simple
+#use Iterator::Simple qw/igrep/;
+#sub get_twin_prime_iterator3 {
+#  my $start = shift || 2;
+#  return igrep { is_prime($_+2) } prime_iterator($start);
+#}
+
+# Not very efficient, using object iterator and peek.
+sub get_twin_prime_iterator4 {
+  my $p = shift || 2;
+  my $it = Math::Prime::Util::prime_iterator_object($p);
+  $p = $it->value();
+  return sub {
+    $it->next() while $it->peek() - $it->value() != 2;
+    $it->iterate();
+  };
+}
+
 my $twinit = get_twin_prime_iterator2();
 for (1..$count) {
   print $twinit->(), "\n";

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