[#3] External functional loops

Author: magicprinc

jOOL-java-8/src/main/java/org/jooq/lambda/Loops.java

@@ -0,0 +1,211 @@
+package org.jooq.lambda;
+
+import org.jooq.lambda.tuple.Tuple4;
+
+import java.util.Arrays;
+import java.util.LongSummaryStatistics;
+import java.util.function.IntConsumer;
+import java.util.function.IntUnaryOperator;
+import java.util.function.LongConsumer;
+import java.util.function.LongPredicate;
+import java.util.function.Predicate;
+
+/** External lambda "for"-loops. */
+public class Loops {
+  private Loops () {}//static utils
+
+
+  /**
+   Simple loop (numberOfRepetitions .. 0].
+   <pre>{@code
+   while (numberOfRepetitions-- > 0)
+     body.run();
+   }</pre>
+   */
+  public static void loop (long numberOfRepetitions, Runnable body) {
+    while (numberOfRepetitions-- > 0) {
+      body.run();
+    }
+  }
+
+  /**
+   Simple while-loop (numberOfRepetitions .. 0].
+   <pre>{@code}
+   while (numberOfRepetitions-- > 0)
+     body.accept(numberOfRepetitions);
+   }</pre>
+   */
+  public static void loop (long numberOfRepetitions, LongConsumer body) {
+    while (numberOfRepetitions-- > 0) {
+      body.accept(numberOfRepetitions);
+    }
+  }
+
+  /**
+   Simple for-loop [0 .. numberOfRepetitions).
+   <pre>{@code}
+   for (int i=0; i&lt;max; i++)
+     body.accept(i);
+   }</pre>
+   */
+  public static void forLoop (int maxExclusive, IntConsumer body) {
+    for (int i=0; i<maxExclusive; i++) {
+      body.accept(i);
+    }
+  }
+
+  /**
+   Simple loop (numberOfRepetitions .. 0] with extra condition.
+   <pre>{@code
+   while (numberOfRepetitions-- > 0 && body.test(numberOfRepetitions)) {}
+   }</pre>
+   @param body do-while Predicate: loops while it is true and numberOfRepetitions &gt; 0
+   */
+  public static void loopWhile (long numberOfRepetitions, LongPredicate body) {
+    //noinspection StatementWithEmptyBody
+    while (numberOfRepetitions-- > 0 && body.test(numberOfRepetitions)) {
+      // do while
+    }
+  }
+
+  // Ad-Hoc JMH (not for serious benchmarks)
+
+  static final long NANO = 1000_000_000L;
+
+  /** Similar to {@link #loop(long, Runnable)}, but with metrics */
+  public static Tuple4<Long, LongSummaryStatistics, Exception, String> loopMeasured (long numberOfRepetitions, Runnable body) {
+    LongSummaryStatistics st = new LongSummaryStatistics();
+    Exception ex = null;
+    long n = System.nanoTime();
+
+    while (numberOfRepetitions-- > 0) {
+      long t = System.nanoTime();
+      try {
+        body.run();
+      } catch (Exception showStopper) {
+        ex = showStopper;
+        break;
+      } finally {
+        st.accept(System.nanoTime() - t);
+      }
+    }
+    n = System.nanoTime() - n;
+
+    StringBuilder sb = new StringBuilder(200);// ≤ ≥
+    sb.append("LOOP: ").append(st.getCount())
+        .append(" nanos= ").append(st.getSum()).append(" ≤ ").append(n)
+        .append(" ~ op/sec= ");
+    if (st.getSum() > 0) {
+      sb.append((st.getCount() * NANO) / st.getSum()).append(" ≥ ");
+    }
+    sb.append((st.getCount() * NANO) / Math.max(n, 1));
+    if (st.getCount()>0) {
+      sb.append(" ~ nano/op= ").append(st.getSum() / st.getCount()).append(" ≤ ").append(n / st.getCount());
+    }
+    sb.append(" min<avg<max= ").append(st.getMin())
+        .append(" < ").append(st.getAverage())
+        .append(" < ").append(st.getMax());
+    return new Tuple4<>(n, st, ex, sb.toString());
+  }
+
+  /** Similar to {@link #loop(long, Runnable)}, but with metrics and warm-up */
+  public static Tuple4<Long, LongSummaryStatistics, Exception, String> loopMeasuredWarm (long numberOfRepetitions, Runnable body) {
+    long warmCnt = Math.min(50_000, numberOfRepetitions/10+10);
+
+    loop(warmCnt, body);
+
+    return loopMeasured(numberOfRepetitions, body);
+  }
+
+
+  public static class Incrementer {
+    protected final int[] indexes;
+    private final IntUnaryOperator maxForIndex;
+
+    /** All indexes have the same max and rotate in range [0..maxExclusive)
+     @param degree size of index vector = how many nested for-loops
+     @param maxExclusive number of repetitions: every index variable rotates in range [0..maxExclusive)
+     */
+    public Incrementer (int degree, final int maxExclusive) {
+      assert degree > 0 : "degree must be > 0, but "+degree;
+      assert maxExclusive > 0 : "maxExclusive must be > 0, but "+maxExclusive;
+
+      indexes = new int[degree];
+      maxForIndex = (index) -> maxExclusive;
+      init();
+    }//new
+
+    /**
+     * Permutation with repetition. Every index has its own max.
+     * @param maxExclusive all indexes have their own max and rotate in range [0..maxExclusive[index])
+     */
+    public Incrementer (final int[] maxExclusive) {
+      assert maxExclusive.length > 0 : "degree must be > 0, but "+maxExclusive.length;
+
+      indexes = new int[maxExclusive.length];
+      maxForIndex = (index) -> maxExclusive[index];
+      init();
+    }//new
+
+    protected void init () {}
+
+    public int degree () {
+      return indexes.length;
+    }
+
+    public int indexAt (int indexIndex) {
+      return indexes[indexIndex];
+    }
+
+    public int maxAt (int indexIndex) {
+      return maxForIndex.applyAsInt(indexIndex);
+    }
+
+    @Override public String toString () {
+      return "Incrementer"+ Arrays.toString(indexes);
+    }
+
+
+    /**
+     Increments index vector (array with indexes) by 1.
+     E.g. for base 2: 0,0,0→0,0,1→0,1,0
+     Emulates one step in multi-nested-for loop.
+
+     @return we "overflowed" the array size = all indexes have reached their max-1
+     @see #forLoop(Predicate)
+     */
+    public boolean incrementIndexVector () {
+      final int len = indexes.length;
+
+      for (int i = 0; i < len; ) {
+        if (++indexes[i] < maxForIndex.applyAsInt(i)) {
+          return false;
+
+        } else {// overflow
+          indexes[i] = 0;// e.g. [10]: 09 → 10
+          i++;
+        }
+      }
+      return true;
+    }
+
+    /**
+     * Permutation with repetition.
+     * @param loopBody receive this Incrementer with indexes and maxExclusive, must return boolean searchIsOver/found
+     * @return searchIsOver/found
+     */
+    public boolean forLoop (Predicate<Incrementer> loopBody) {
+      while (true) {
+        boolean found = loopBody.test(this);
+        if (found) {
+          return true;
+        }
+        boolean overflow = incrementIndexVector();
+        if (overflow) {
+          return false;
+        }
+      }
+    }
+  }//Incrementer
+
+}