implement java.util.Random and java.lang.Math.random in Java

classpath/java-lang.cpp

@@ -519,31 +519,6 @@ Java_java_lang_Math_pow(JNIEnv*, jclass, jdouble val, jdouble exp)
   return pow(val, exp);
 }
 
-extern "C" JNIEXPORT void JNICALL
-Java_java_lang_Math_natRandomInitialize(JNIEnv*, jclass, jlong val)
-{
-#ifdef WIN32
-  srand(val);
-#else
-  srand48(val);
-#endif
-}
-
-extern "C" JNIEXPORT jdouble JNICALL
-Java_java_lang_Math_natRandom(JNIEnv*, jclass)
-{
-#ifdef WIN32
-  double r = static_cast<double>(rand()) / static_cast<double>(RAND_MAX);
-  if (r < 0 or r >= 1) {
-    return 0;
-  } else {
-    return r;
-  }
-#else
-  return drand48();
-#endif
-}
-
 extern "C" JNIEXPORT jdouble JNICALL
 Java_java_lang_Math_floor(JNIEnv*, jclass, jdouble val)
 {

classpath/java/lang/Math.java

@@ -10,10 +10,12 @@
 
 package java.lang;
 
+import java.util.Random;
+
 public final class Math {
   public static final double E = 2.718281828459045;
   public static final double PI = 3.141592653589793;
-  private static boolean randomInitialized = false;
+  private static final Random random = new Random();
 
   private Math() { }
 
@@ -74,17 +76,9 @@ public final class Math {
   }
 
   public static double random() {
-    if (randomInitialized) {
-      natRandomInitialize(System.currentTimeMillis());
-      randomInitialized = true;
-    }
-    return natRandom();
+    return random.nextDouble();
   }
 
-  public static native void natRandomInitialize(long val);
-
-  public static native double natRandom();
-
   public static native double floor(double v);
 
   public static native double ceil(double v);

classpath/java/util/Random.java

@@ -11,15 +11,54 @@
 package java.util;
 
 public class Random {
-  public int nextInt(int n) {
-    return nextInt() % n;
+  private static final long Mask = 0x5DEECE66DL;
+
+  private static long nextSeed = 0;
+
+  private long seed;
+
+  public Random(long seed) {
+    setSeed(seed);
+  }
+
+  public Random() {
+    setSeed((nextSeed++) ^ System.currentTimeMillis());
+  }
+
+  public void setSeed(long seed) {
+    this.seed = (seed ^ Mask) & ((1L << 48) - 1);
+  }
+
+  protected int next(int bits) {
+    seed = ((seed * Mask) + 0xBL) & ((1L << 48) - 1);
+    return (int) (seed >>> (48 - bits));
+  }
+
+  public int nextInt(int limit) {
+    if (limit <= 0) {
+      throw new IllegalArgumentException();
+    }
+    
+    if ((limit & -limit) == limit) {
+      // limit is a power of two
+      return (int) ((limit * (long) next(31)) >> 31);
+    }
+    
+    int bits;
+    int value;
+    do {
+      bits = next(31);
+      value = bits % limit;
+    } while (bits - value + (limit - 1) < 0);
+
+    return value;
   }
 
   public int nextInt() {
-    return (int)(Math.random()*Integer.MAX_VALUE);
+    return next(32);
   }
 
   public double nextDouble() {
-    return Math.random();
+    return (((long) next(26) << 27) + next(27)) / (double) (1L << 53);
   }
 }