Implement LiLSkipFunction

src/main/java/gr/james/sampling/LiLSampling.java

@@ -79,4 +79,31 @@ long skipLength(long streamSize, int sampleSize, Random random) {
         W = W * Math.pow(random2, 1.0 / sampleSize);
         return skip;
     }
+
+    @Deprecated
+    private static class LiLSkipFunction implements SkipFunction {
+        private final int sampleSize;
+        private final Random random;
+        private double W;
+
+        public LiLSkipFunction(int sampleSize, Random random) {
+            this.sampleSize = sampleSize;
+            this.random = random;
+            this.W = Math.pow(RandomSamplingUtils.randomExclusive(random), 1.0 / sampleSize);
+        }
+
+        @Override
+        public long skip() throws StreamOverflowException {
+            final double random1 = RandomSamplingUtils.randomExclusive(random);
+            final double random2 = RandomSamplingUtils.randomExclusive(random);
+            long skip = (long) (Math.log(random1) / Math.log(1 - W));
+            assert skip >= 0 || skip == Long.MIN_VALUE;
+            if (skip == Long.MIN_VALUE) {  // Sometimes when W is very small, 1 - W = 1 and Math.log(1) = +0 instead of -0
+                skip = Long.MAX_VALUE;     // This results in negative infinity skip
+            }
+            // W = W * Math.exp(Math.log(random2) / sampleSize);
+            W = W * Math.pow(random2, 1.0 / sampleSize);
+            return skip;
+        }
+    }
 }