Fix build following cms/cpc recent PR

Author: freakyzoidberg

src/main/java/org/apache/datasketches/count/CountMinSketch.java

@@ -22,8 +22,8 @@
 import org.apache.datasketches.common.Family;
 import org.apache.datasketches.common.SketchesArgumentException;
 import org.apache.datasketches.common.SketchesException;
+import org.apache.datasketches.common.Util;
 import org.apache.datasketches.hash.MurmurHash3;
-import org.apache.datasketches.tuple.Util;
 
 import java.io.ByteArrayOutputStream;
 import java.nio.ByteBuffer;
@@ -39,6 +39,9 @@ public class CountMinSketch {
   private final long[] sketchArray_;
   private long totalWeight_;
 
+  // Thread-local ByteBuffer to avoid allocations in hot paths
+  private static final ThreadLocal<ByteBuffer> LONG_BUFFER =
+          ThreadLocal.withInitial(() -> ByteBuffer.allocate(8));
 
   private enum Flag {
     IS_EMPTY;
@@ -57,30 +60,59 @@ int mask() {
    * @param seed The base hash seed
    */
   CountMinSketch(final byte numHashes, final int numBuckets, final long seed) {
-    numHashes_ = numHashes;
-    numBuckets_ = numBuckets;
-    seed_ = seed;
-    hashSeeds_ = new long[numHashes];
-    sketchArray_ = new long[numHashes * numBuckets];
-    totalWeight_ = 0;
+    // Validate numHashes
+    if (numHashes <= 0) {
+      throw new SketchesArgumentException("Number of hash functions must be positive, got: " + numHashes);
+    }
 
+    // Validate numBuckets with clear mathematical justification
+    if (numBuckets <= 0) {
+      throw new SketchesArgumentException("Number of buckets must be positive, got: " + numBuckets);
+    }
     if (numBuckets < 3) {
-      throw new SketchesArgumentException("Using fewer than 3 buckets incurs relative error greater than 1.");
+      throw new SketchesArgumentException("Number of buckets must be at least 3 to ensure relative error ≤ 1.0. " +
+          "With " + numBuckets + " buckets, relative error would be " + String.format("%.3f", Math.exp(1.0) / numBuckets));
+    }
+
+    // Check for potential overflow in array size calculation
+    // Use long arithmetic to detect overflow before casting
+    final long totalSize = (long) numHashes * (long) numBuckets;
+    if (totalSize > Integer.MAX_VALUE) {
+      throw new SketchesArgumentException("Sketch array size would overflow: " + numHashes + " * " + numBuckets +
+          " = " + totalSize + " > " + Integer.MAX_VALUE);
     }
 
     // This check is to ensure later compatibility with a Java implementation whose maximum size can only
     // be 2^31-1.  We check only against 2^30 for simplicity.
-    if (numBuckets * numHashes >= 1 << 30) {
-      throw new SketchesArgumentException("These parameters generate a sketch that exceeds 2^30 elements. \n" +
-          "Try reducing either the number of buckets or the number of hash functions.");
+    if (totalSize >= (1L << 30)) {
+      throw new SketchesArgumentException("Sketch would require excessive memory: " + numHashes + " * " + numBuckets +
+          " = " + totalSize + " elements (~" + String.format("%.1f", totalSize * 8.0 / (1024 * 1024 * 1024)) + " GB). " +
+          "Consider reducing numHashes or numBuckets.");
     }
 
+    numHashes_ = numHashes;
+    numBuckets_ = numBuckets;
+    seed_ = seed;
+    hashSeeds_ = new long[numHashes];
+    sketchArray_ = new long[(int) totalSize];
+    totalWeight_ = 0;
+
     Random rand = new Random(seed);
     for (int i = 0; i < numHashes; i++) {
       hashSeeds_[i] = rand.nextLong();
     }
   }
 
+  /**
+   * Efficiently converts a long to byte array using thread-local buffer to avoid allocations.
+   */
+  private static byte[] longToBytes(final long value) {
+    final ByteBuffer buffer = LONG_BUFFER.get();
+    buffer.clear();
+    buffer.putLong(value);
+    return buffer.array();
+  }
+
   private long[] getHashes(byte[] item) {
     long[] updateLocations = new long[numHashes_];
 
@@ -171,8 +203,7 @@ public static int suggestNumBuckets(double relativeError) {
    * @param weight The weight of the item.
    */
   public void update(final long item, final long weight) {
-    byte[] longByte = ByteBuffer.allocate(8).putLong(item).array();
-    update(longByte, weight);
+    update(longToBytes(item), weight);
   }
 
   /**
@@ -211,8 +242,7 @@ public void update(final byte[] item, final long weight) {
    * @return Estimated frequency.
    */
   public long getEstimate(final long item) {
-    byte[] longByte = ByteBuffer.allocate(8).putLong(item).array();
-    return getEstimate(longByte);
+    return getEstimate(longToBytes(item));
   }
 
   /**
@@ -241,8 +271,9 @@ public long getEstimate(final byte[] item) {
 
     long[] hashLocations = getHashes(item);
     long res = sketchArray_[(int) hashLocations[0]];
-    for (long h : hashLocations) {
-      res = Math.min(res,  sketchArray_[(int) h]);
+    // Start from index 1 to avoid processing first element twice
+    for (int i = 1; i < hashLocations.length; i++) {
+      res = Math.min(res, sketchArray_[(int) hashLocations[i]]);
     }
 
     return res;
@@ -254,8 +285,7 @@ public long getEstimate(final byte[] item) {
    * @return Upper bound of estimated frequency.
    */
   public long getUpperBound(final long item) {
-    byte[] longByte = ByteBuffer.allocate(8).putLong(item).array();
-    return getUpperBound(longByte);
+    return getUpperBound(longToBytes(item));
   }
 
   /**
@@ -291,8 +321,7 @@ public long getUpperBound(final byte[] item) {
    * @return Lower bound of estimated frequency.
    */
   public long getLowerBound(final long item) {
-    byte[] longByte = ByteBuffer.allocate(8).putLong(item).array();
-    return getLowerBound(longByte);
+    return getLowerBound(longToBytes(item));
   }
 
   /**

src/test/java/org/apache/datasketches/cpc/CpcSketchCrossLanguageTest.java

@@ -31,6 +31,7 @@
 import java.io.IOException;
 import java.nio.file.Files;
 
+import org.apache.datasketches.memory.Memory;
 import org.testng.annotations.Test;
 
 /**
@@ -89,7 +90,7 @@ public void checkAllFlavorsGo() throws IOException {
     int flavorIdx = 0;
     for (int n: nArr) {
       final byte[] bytes = Files.readAllBytes(goPath.resolve("cpc_n" + n + "_go.sk"));
-      final CpcSketch sketch = CpcSketch.heapify(Memory.wrap(bytes));
+      final CpcSketch sketch = CpcSketch.heapify(MemorySegment.ofArray(bytes));
       assertEquals(sketch.getFlavor(), flavorArr[flavorIdx++]);
       assertEquals(sketch.getEstimate(), n, n * 0.02);
     }