fix: init with NaN

Author: proost

src/main/java/org/apache/datasketches/req/ReqSerDe.java

@@ -20,7 +20,6 @@
 package org.apache.datasketches.req;
 
 import static java.lang.Math.max;
-import static java.lang.Math.min;
 import static java.lang.Math.round;
 
 import java.lang.foreign.MemorySegment;
@@ -204,11 +203,17 @@ static final Compactor extractCompactor(final PositionalSegment posSeg, final bo
     final int count = posSeg.getInt();
     final float[] arr = new float[count];
     posSeg.getFloatArray(arr, 0, count);
-    float minItem = Float.MAX_VALUE;
-    float maxItem = -Float.MAX_VALUE;
+    float minItem = Float.NaN;
+    float maxItem = Float.NaN;
     for (int i = 0; i < count; i++) {
-      minItem = min(minItem, arr[i]);
-      maxItem = max(maxItem, arr[i]);
+      final float item = arr[i];
+      if (Float.isNaN(minItem)) {
+        minItem = item;
+        maxItem = item;
+      } else {
+        if (item < minItem) { minItem = item; }
+        if (item > maxItem) { maxItem = item; }
+      }
     }
     final int delta = 2 * sectionSize * numSections;
     final int nomCap = 2 * delta;

src/test/java/org/apache/datasketches/req/ReqCompactorTest.java

@@ -144,4 +144,26 @@ private static void checkSerDeMixedImpl(final int k, final boolean hra) {
     assertEquals(compactor.minItem, (float) -half);
     assertEquals(compactor.maxItem, (float) (half - 1));
   }
+
+  @Test
+  public void checkSerDeWithInfiniteValues() {
+    checkSerDeInfiniteImpl(12, false);
+    checkSerDeInfiniteImpl(12, true);
+  }
+
+  private static void checkSerDeInfiniteImpl(final int k, final boolean hra) {
+    final ReqCompactor c1 = new ReqCompactor((byte)0, hra, k, null);
+    final FloatBuffer fbuf = c1.getBuffer();
+
+    fbuf.append(Float.POSITIVE_INFINITY);
+    fbuf.append(1);
+    fbuf.append(Float.NEGATIVE_INFINITY);
+    fbuf.append(-1);
+
+    final byte[] c1ser = c1.toByteArray();
+    final PositionalSegment posSeg = PositionalSegment.wrap(MemorySegment.ofArray(c1ser));
+    final Compactor compactor = ReqSerDe.extractCompactor(posSeg, fbuf.isSorted(), hra);
+    assertEquals(compactor.minItem, Float.NEGATIVE_INFINITY);
+    assertEquals(compactor.maxItem, Float.POSITIVE_INFINITY);
+  }
 }