Add getInts api for HostMemoryBuffer and UnsafeMemoryAccessor (#17767)

Add getInts api for HostMemoryBuffer and UnsafeMemoryAccessor.

This pr is part of an optimization for optimizing concating validity buffer in kudo. It has no side effects, there already exists similar apis for `getShorts`, `getLongs`, `getBytes` etc. It didn't exist before because it was  not used, now we need to use it.

Authors:
  - Renjie Liu (https://github.com/liurenjie1024)

Approvers:
  - Liangcai Li (https://github.com/firestarman)
  - Chong Gao (https://github.com/res-life)

URL: #17767

java/src/main/java/ai/rapids/cudf/HostMemoryBuffer.java

@@ -1,6 +1,6 @@
 /*
  *
- *  Copyright (c) 2019-2024, NVIDIA CORPORATION.
+ *  Copyright (c) 2019-2025, NVIDIA CORPORATION.
  *
  *  Licensed under the Apache License, Version 2.0 (the "License");
  *  you may not use this file except in compliance with the License.
@@ -367,6 +367,23 @@ public final int getInt(long offset) {
     return UnsafeMemoryAccessor.getInt(requestedAddress);
   }
 
+  /**
+   * Copy a set of ints to an array from the buffer starting at offset.
+   * @param dst       destination int array
+   * @param dstIndex  starting index within the destination array
+   * @param srcOffset starting offset within this buffer
+   * @param count     number of ints to copy
+   */
+  public final void getInts(int[] dst, long dstIndex, long srcOffset, int count) {
+    assert count >= 0;
+    assert count <= dst.length - dstIndex;
+    assert srcOffset >= 0;
+    long requestedAddress = this.address + srcOffset;
+    addressOutOfBoundsCheck(requestedAddress, count * 4L, "getInts");
+    UnsafeMemoryAccessor.getInts(dst, dstIndex, requestedAddress, count);
+  }
+
+
   /**
    * Sets the Integer value at that offset
    * @param offset - offset from the address

java/src/main/java/ai/rapids/cudf/UnsafeMemoryAccessor.java

@@ -1,6 +1,6 @@
 /*
  *
- *  Copyright (c) 2019, NVIDIA CORPORATION.
+ *  Copyright (c) 2019-2025, NVIDIA CORPORATION.
  *
  *  Licensed under the Apache License, Version 2.0 (the "License");
  *  you may not use this file except in compliance with the License.
@@ -154,6 +154,19 @@ public static int getInt(long address) {
     return UNSAFE.getInt(address);
   }
 
+  /**
+   * Copy out an array of ints.
+   * @param dst       where to write the data
+   * @param dstIndex  index into values to start writing at.
+   * @param address   src memory address
+   * @param count     the number of ints to copy
+   * @throws IndexOutOfBoundsException
+   */
+  public static void getInts(int[] dst, long dstIndex, long address, int count) {
+    copyMemory(null, address,
+            dst, UnsafeMemoryAccessor.INT_ARRAY_OFFSET + (dstIndex * 4), count * 4);
+  }
+
   /**
    * Sets the Integer value at that address
    * @param address - memory address

java/src/test/java/ai/rapids/cudf/HostMemoryBufferTest.java

@@ -1,6 +1,6 @@
 /*
  *
- *  Copyright (c) 2019-2024, NVIDIA CORPORATION.
+ *  Copyright (c) 2019-2025, NVIDIA CORPORATION.
  *
  *  Licensed under the Apache License, Version 2.0 (the "License");
  *  you may not use this file except in compliance with the License.
@@ -87,6 +87,20 @@ public void testGetInt() {
     }
   }
 
+  @Test
+  public void testGetInts() {
+    try (HostMemoryBuffer hostMemoryBuffer = HostMemoryBuffer.allocate(16)) {
+      hostMemoryBuffer.setInt(0, 1);
+      hostMemoryBuffer.setInt(4, 2);
+      hostMemoryBuffer.setInt(8, 3);
+      hostMemoryBuffer.setInt(12, 4);
+      int[] expectedInts = new int[] {1, 2, 3, 4};
+      int[] result = new int[expectedInts.length];
+      hostMemoryBuffer.getInts(result, 0, 0, 4);
+      assertArrayEquals(expectedInts, result);
+    }
+  }
+
   @Test
   public void testGetByte() {
     try (HostMemoryBuffer hostMemoryBuffer = HostMemoryBuffer.allocate(16)) {

java/src/test/java/ai/rapids/cudf/UnsafeMemoryAccessorTest.java

@@ -1,6 +1,6 @@
 /*
  *
- *  Copyright (c) 2019-2023, NVIDIA CORPORATION.
+ *  Copyright (c) 2019-2025, NVIDIA CORPORATION.
  *
  *  Licensed under the Apache License, Version 2.0 (the "License");
  *  you may not use this file except in compliance with the License.
@@ -66,6 +66,24 @@ public void setIntAndGetInt() {
     }
   }
 
+  @Test
+  public void setAndGetInts() {
+    int numInts = 289;
+    long address = UnsafeMemoryAccessor.allocate(numInts * 4);
+    try {
+      for (int i = 0; i < numInts; i++) {
+        UnsafeMemoryAccessor.setInt(address + i * 4, i);
+      }
+      int[] ints = new int[numInts];
+      UnsafeMemoryAccessor.getInts(ints, 0, address, numInts);
+      for (int i = 0; i < numInts; i++) {
+        assertEquals(i, ints[i]);
+      }
+    } finally {
+      UnsafeMemoryAccessor.free(address);
+    }
+  }
+
   @Test
   public void setMemoryValue() {
     long address = UnsafeMemoryAccessor.allocate(4);