lib/prime: Fix primality of some large integers [#13492].

* lib/prime.rb: Use accurate sqrt to insure all factors are tested.
  Patch by Marcus Stollsteimer.

* test/test_prime.rb: Adapt test for timeout

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58809 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/prime.rb

@@ -35,7 +35,7 @@ class Integer
     return self >= 2 if self <= 3
     return true if self == 5
     return false unless 30.gcd(self) == 1
-    (7..Math.sqrt(self).to_i).step(30) do |p|
+    (7..Integer.sqrt(self)).step(30) do |p|
       return false if
         self%(p)    == 0 || self%(p+4)  == 0 || self%(p+6)  == 0 || self%(p+10) == 0 ||
         self%(p+12) == 0 || self%(p+16) == 0 || self%(p+22) == 0 || self%(p+24) == 0
@@ -445,7 +445,7 @@ class Prime
 
       segment_min = @max_checked
       segment_max = [segment_min + max_segment_size, max_cached_prime * 2].min
-      root = Integer(Math.sqrt(segment_max).floor)
+      root = Integer.sqrt(segment_max)
 
       segment = ((segment_min + 1) .. segment_max).step(2).to_a
 

test/test_prime.rb

@@ -174,20 +174,21 @@ class TestPrime < Test::Unit::TestCase
   def test_eratosthenes_works_fine_after_timeout
     sieve = Prime::EratosthenesSieve.instance
     sieve.send(:initialize)
+    # simulates that Timeout.timeout interrupts Prime::EratosthenesSieve#compute_primes
+    class << Integer
+      alias_method :org_sqrt, :sqrt
+    end
     begin
-      # simulates that Timeout.timeout interrupts Prime::EratosthenesSieve#compute_primes
-      def sieve.Integer(n)
-        n = super(n)
+      def Integer.sqrt(n)
         sleep 10 if /compute_primes/ =~ caller.first
-        return n
+        org_sqrt(n)
       end
-
       assert_raise(Timeout::Error) do
         Timeout.timeout(0.5) { Prime.each(7*37){} }
       end
     ensure
-      class << sieve
-        remove_method :Integer
+      class << Integer
+        alias_method :sqrt, :org_sqrt
       end
     end