less random generations in Random::Formatter#choose.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60309 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/securerandom.rb

@@ -243,7 +243,31 @@ module Random::Formatter
   # +NotImplementedError+ is raised.
   private def choose(source, n)
     size = source.size
-    n.times.map {source[random_number(size)]}.join('')
+    m = 1
+    limit = size
+    while limit * size <= 0x100000000
+      limit *= size
+      m += 1
+    end
+    result = ''.dup
+    while m <= n
+      rs = random_number(limit)
+      is = rs.digits(size)
+      (m-is.length).times { is << 0 }
+      result << source.values_at(*is).join('')
+      n -= m
+    end
+    if 0 < n
+      rs = random_number(limit)
+      is = rs.digits(size)
+      if is.length < n
+        (n-is.length).times { is << 0 }
+      else
+        is.pop while n < is.length
+      end
+      result.concat source.values_at(*is).join('')
+    end
+    result
   end
 
   ALPHANUMERIC = [*'A'..'Z', *'a'..'z', *'0'..'9']

test/test_securerandom.rb

@@ -144,9 +144,10 @@ end
   end
 
   def test_alphanumeric
-    65.times do |idx|
-      an = @it.alphanumeric
-      assert_match(/^[0-9a-zA-Z]+$/, an)
+    65.times do |n|
+      an = @it.alphanumeric(n)
+      assert_match(/^[0-9a-zA-Z]*$/, an)
+      assert_equal(n, an.length)
     end
   end