[libmath-prime-util-perl] 56/181: Make sure PP znprimroot handles non-cyclic nputs quickly

[Partha P. Mukherjee]

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ppm-guest pushed a commit to annotated tag v0.36
in repository libmath-prime-util-perl.

commit a193d10d6fc15bb04a6513f542f8e2c7bb1e6517
Author: Dana Jacobsen <dana at acm.org>
Date:   Sat Dec 28 14:15:23 2013 -0800

    Make sure PP znprimroot handles non-cyclic nputs quickly
---
 lib/Math/Prime/Util.pm | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/lib/Math/Prime/Util.pm b/lib/Math/Prime/Util.pm
index 64de45b..fa11fa9 100644
--- a/lib/Math/Prime/Util.pm
+++ b/lib/Math/Prime/Util.pm
@@ -1723,10 +1723,15 @@ sub _generic_znprimroot {
   my($n) = @_;
   $n = -$n if defined $n && $n =~ /^-\d+/;   # TODO: fix this for string bigints
   _validate_num($n) || _validate_positive_integer($n);
-  return if $n == 0;
-  return $n-1 if $n <= 4;
+  if ($n <= 4) {
+    return if $n == 0;
+    return $n-1;
+  }
+  return if $n % 4 == 0;
   my $a = 1;
   my $phi = euler_phi($n);
+  # Check that a primitive root exists.
+  return if !is_prob_prime($n) && $phi != carmichael_lambda($n);
   my @exp = map { int($phi/$_->[0]) } factor_exp($phi);
   #print "phi: $phi  factors: ", join(",",factor($phi)), "\n";
   #print "  exponents: ", join(",", @exp), "\n";

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