Data commit

Task/Legendre-prime-counting-function/Perl/legendre-prime-counting-function.pl

@@ -0,0 +1,29 @@
+#!/usr/bin/perl
+
+use strict; # https://rosettacode.org/wiki/Legendre_prime_counting_function
+use warnings;
+no warnings qw(recursion);
+use ntheory qw( nth_prime prime_count );
+
+my (%cachephi, %cachepi);
+
+sub phi
+  {
+  return $cachephi{"@_"} //= do {
+    my ($x, $aa) = @_;
+    $aa <= 0 ? $x : phi($x, $aa - 1) - phi(int $x / nth_prime($aa), $aa - 1) };
+  }
+
+sub pi
+  {
+  return $cachepi{$_[0]} //= do {
+    my $n = shift;
+    $n < 2 ? 0 : do{ my $aa = pi(int sqrt $n); phi($n, $aa) + $aa - 1 } };
+  }
+
+print "e             n   Legendre    ntheory\n",
+      "-             -   --------    -------\n";
+for (1 .. 9)
+  {
+  printf "%d  %12d %10d %10d\n", $_, 10**$_, pi(10**$_), prime_count(10**$_);
+  }