Adding Random to standard libraries (#475)

* Adding Random to standard libraries

Adds a new passive class "Random" to the standard libraries.
Each instance of Random encapsulates a seed of its own.
Technically, this may be wasteful -- possibly one seed per
thread might do, but this will facilitate debugging programs
with random numbers.

* Added a global random function with a thread-local seed

* Changed the int hack to an embed type

* Changed int to void type for less confusion

* Change the name of the test to avoid name clashes

* Update Random.enc

bundles/standard/Random.enc

@@ -0,0 +1,35 @@
+embed
+body
+__thread unsigned seed;
+end
+
+-- Random number generator with thread-local seed
+def random(max:int) : int
+  embed int
+    if (seed == 0)
+      {
+        seed = (unsigned) time(NULL);
+      }
+    rand_r(&seed) % #{max};
+  end    
+
+-- Simple random number generator encapsulating a seed of its own
+passive class Random
+  seed:embed unsigned int end
+  -- Trace funcition required because of the embed type of seed
+  def Random_trace() : void
+    ()
+  -- Initialisation always with a seed in [0..2^32)
+  def init(seed:int) : void {
+    assertFalse(seed < 0) ;
+    assertFalse(seed > 4294967295) ; -- for want of an Encore 2^32 operator
+    embed void
+      _this->_enc__field_seed = (unsigned) #{seed};
+    end;
+    }
+  -- Returns random % max where max [0..2^32)
+  def random(max:int) : int
+    embed int
+      rand_r((unsigned *) &(_this->_enc__field_seed)) % #{max};
+    end
+

src/tests/encore/stdlib/random_test.enc

@@ -0,0 +1,10 @@
+import Random
+
+class Main
+  def main() : void
+    let
+      r = new Random(100)
+      v1 = r.random(1)
+      v2 = random(1)
+    in
+      print("{}\n{}\n", v1, v2)

src/tests/encore/stdlib/random_test.out

@@ -0,0 +1,2 @@
+0
+0