GH-39680: [Java] enable half float support on Java module

java/memory/memory-core/src/main/java/org/apache/arrow/memory/ArrowBuf.java

@@ -29,6 +29,7 @@
 
 import org.apache.arrow.memory.BaseAllocator.Verbosity;
 import org.apache.arrow.memory.util.CommonUtil;
+import org.apache.arrow.memory.util.Float16;
 import org.apache.arrow.memory.util.HistoricalLog;
 import org.apache.arrow.memory.util.MemoryUtil;
 import org.apache.arrow.util.Preconditions;
@@ -346,6 +347,29 @@ public void setLong(long index, long value) {
     MemoryUtil.UNSAFE.putLong(addr(index), value);
   }
 
+  /**
+   * Get float16 value stored at a particular index in the
+   * underlying memory chunk this ArrowBuf has access to.
+   * @param index index (0 based relative to this ArrowBuf)
+   *              where the value will be read from
+   * @return 4 byte float value
+   */
+  public short getFloat16(long index) {
+    return getShort(index);
+  }
+
+
+  /**
+   * Set float16 value at a particular index in the
+   * underlying memory chunk this ArrowBuf has access to.
+   * @param index index (0 based relative to this ArrowBuf)
+   *              where the value will be written
+   * @param value value to write
+   */
+  public void setFloat16(long index, float value) {
+    setShort(index, Float16.toFloat16(value));
+  }
+
   /**
    * Get float value stored at a particular index in the
    * underlying memory chunk this ArrowBuf has access to.

java/memory/memory-core/src/main/java/org/apache/arrow/memory/util/Float16.java

@@ -0,0 +1,262 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.arrow.memory.util;
+
+
+import org.apache.arrow.util.VisibleForTesting;
+
+/**
+ * The class is a utility class to manipulate half-precision 16-bit
+ * <a href="https://en.wikipedia.org/wiki/Half-precision_floating-point_format">IEEE 754</a>
+ * floating point data types (also called fp16 or binary16). A half-precision float can be
+ * created from or converted to single-precision floats, and is stored in a short data type.
+ * The IEEE 754 standard specifies an float16 as having the following format:
+ * <ul>
+ * <li>Sign bit: 1 bit</li>
+ * <li>Exponent width: 5 bits</li>
+ * <li>Significand: 10 bits</li>
+ * </ul>
+ *
+ * <p>The format is laid out as follows:</p>
+ * <pre>
+ * 1   11111   1111111111
+ * ^   --^--   -----^----
+ * sign  |          |_______ significand
+ *       |
+ *      -- exponent
+ * </pre>
+ * Half-precision floating points can be useful to save memory and/or
+ * bandwidth at the expense of range and precision when compared to single-precision
+ * floating points (float32).
+ * Ref: https://android.googlesource.com/platform/libcore/+/master/luni/src/main/java/libcore/util/FP16.java
+ */
+public class Float16 {
+  // Positive infinity of type half-precision float.
+  private static final short POSITIVE_INFINITY = (short) 0x7c00;
+  // A Not-a-Number representation of a half-precision float.
+  private static final short NaN = (short) 0x7e00;
+  // The bitmask to and a number with to obtain the sign bit.
+  private static final int SIGN_MASK = 0x8000;
+  // The offset to shift by to obtain the exponent bits.
+  private static final int EXPONENT_SHIFT = 10;
+  // The bitmask to and a number shifted by EXPONENT_SHIFT right, to obtain exponent bits.
+  private static final int SHIFTED_EXPONENT_MASK = 0x1f;
+  // The bitmask to and a number with to obtain significand bits.
+  private static final int SIGNIFICAND_MASK = 0x3ff;
+  // The offset of the exponent from the actual value.
+  private static final int EXPONENT_BIAS = 15;
+  // The offset to shift by to obtain the sign bit.
+  private static final int SIGN_SHIFT = 15;
+  // The bitmask to AND with to obtain exponent and significand bits.
+  private static final int EXPONENT_SIGNIFICAND_MASK = 0x7fff;
+
+  private static final int FP32_SIGN_SHIFT = 31;
+  private static final int FP32_EXPONENT_SHIFT = 23;
+  private static final int FP32_SHIFTED_EXPONENT_MASK = 0xff;
+  private static final int FP32_SIGNIFICAND_MASK = 0x7fffff;
+  private static final int FP32_EXPONENT_BIAS = 127;
+  private static final int FP32_QNAN_MASK = 0x400000;
+  private static final int FP32_DENORMAL_MAGIC = 126 << 23;
+  private static final float FP32_DENORMAL_FLOAT = Float.intBitsToFloat(FP32_DENORMAL_MAGIC);
+
+  /**
+   * Returns true if the specified half-precision float value represents
+   * a Not-a-Number, false otherwise.
+   *
+   * @param h A half-precision float value
+   * @return True if the value is a NaN, false otherwise
+   *
+   */
+  @VisibleForTesting
+  public static boolean isNaN(short h) {
+    return (h & EXPONENT_SIGNIFICAND_MASK) > POSITIVE_INFINITY;
+  }
+
+  /**
+   * <p>Compares the two specified half-precision float values. The following
+   * conditions apply during the comparison:</p>
+   *
+   * <ul>
+   * <li>NaN is considered by this method to be equal to itself and greater
+   * than all other half-precision float values (including {@code #POSITIVE_INFINITY})</li>
+   * <li>POSITIVE_ZERO is considered by this method to be greater than NEGATIVE_ZERO.</li>
+   * </ul>
+   *
+   * @param x The first half-precision float value to compare.
+   * @param y The second half-precision float value to compare
+   *
+   * @return  The value {@code 0} if {@code x} is numerically equal to {@code y}, a
+   *          value less than {@code 0} if {@code x} is numerically less than {@code y},
+   *          and a value greater than {@code 0} if {@code x} is numerically greater
+   *          than {@code y}
+   *
+   */
+  @VisibleForTesting
+  public static int compare(short x, short y) {
+    boolean xIsNaN = isNaN(x);
+    boolean yIsNaN = isNaN(y);
+
+    if (!xIsNaN && !yIsNaN) {
+      int first = ((x & SIGN_MASK) != 0 ? 0x8000 - (x & 0xffff) : x & 0xffff);
+      int second = ((y & SIGN_MASK) != 0 ? 0x8000 - (y & 0xffff) : y & 0xffff);
+      // Returns true if the first half-precision float value is less
+      // (smaller toward negative infinity) than the second half-precision float value.
+      if (first < second) {
+        return -1;
+      }
+
+      // Returns true if the first half-precision float value is greater
+      // (larger toward positive infinity) than the second half-precision float value.
+      if (first > second) {
+        return 1;
+      }
+    }
+
+    // Collapse NaNs, akin to halfToIntBits(), but we want to keep
+    // (signed) short value types to preserve the ordering of -0.0
+    // and +0.0
+    short xBits = xIsNaN ? NaN : x;
+    short yBits = yIsNaN ? NaN : y;
+    return (xBits == yBits ? 0 : (xBits < yBits ? -1 : 1));
+  }
+
+  /**
+   * Converts the specified half-precision float value into a
+   * single-precision float value. The following special cases are handled:
+   * If the input is NaN, the returned value is Float NaN.
+   * If the input is POSITIVE_INFINITY or NEGATIVE_INFINITY, the returned value is respectively
+   *   Float POSITIVE_INFINITY or Float NEGATIVE_INFINITY.
+   * If the input is 0 (positive or negative), the returned value is +/-0.0f.
+   * Otherwise, the returned value is a normalized single-precision float value.
+   *
+   * @param b The half-precision float value to convert to single-precision
+   * @return A normalized single-precision float value
+   */
+  @VisibleForTesting
+  public static float toFloat(short b) {
+    int bits = b & 0xffff;
+    int s = bits & SIGN_MASK;
+    int e = (bits >>> EXPONENT_SHIFT) & SHIFTED_EXPONENT_MASK;
+    int m = (bits) & SIGNIFICAND_MASK;
+    int outE = 0;
+    int outM = 0;
+    if (e == 0) { // Denormal or 0
+      if (m != 0) {
+        // Convert denorm fp16 into normalized fp32
+        float o = Float.intBitsToFloat(FP32_DENORMAL_MAGIC + m);
+        o -= FP32_DENORMAL_FLOAT;
+        return s == 0 ? o : -o;
+      }
+    } else {
+      outM = m << 13;
+      if (e == 0x1f) { // Infinite or NaN
+        outE = 0xff;
+        if (outM != 0) { // SNaNs are quieted
+          outM |= FP32_QNAN_MASK;
+        }
+      } else {
+        outE = e - EXPONENT_BIAS + FP32_EXPONENT_BIAS;
+      }
+    }
+    int out = (s << 16) | (outE << FP32_EXPONENT_SHIFT) | outM;
+    return Float.intBitsToFloat(out);
+  }
+
+  /**
+   * Converts the specified single-precision float value into a
+   * half-precision float value. The following special cases are handled:
+   *
+   * If the input is NaN, the returned value is NaN.
+   * If the input is Float POSITIVE_INFINITY or Float NEGATIVE_INFINITY,
+   *   the returned value is respectively POSITIVE_INFINITY or NEGATIVE_INFINITY.
+   * If the input is 0 (positive or negative), the returned value is
+   *   POSITIVE_ZERO or NEGATIVE_ZERO.
+   * If the input is a less than MIN_VALUE, the returned value
+   *   is flushed to POSITIVE_ZERO or NEGATIVE_ZERO.
+   * If the input is a less than MIN_NORMAL, the returned value
+   *   is a denorm half-precision float.
+   * Otherwise, the returned value is rounded to the nearest
+   *   representable half-precision float value.
+   *
+   * @param f The single-precision float value to convert to half-precision
+   * @return A half-precision float value
+   */
+  public static short toFloat16(float f) {
+    int bits = Float.floatToRawIntBits(f);
+    int s = (bits >>> FP32_SIGN_SHIFT);
+    int e = (bits >>> FP32_EXPONENT_SHIFT) & FP32_SHIFTED_EXPONENT_MASK;
+    int m = (bits) & FP32_SIGNIFICAND_MASK;
+    int outE = 0;
+    int outM = 0;
+    if (e == 0xff) { // Infinite or NaN
+      outE = 0x1f;
+      outM = m != 0 ? 0x200 : 0;
+    } else {
+      e = e - FP32_EXPONENT_BIAS + EXPONENT_BIAS;
+      if (e >= 0x1f) { // Overflow
+        outE = 0x1f;
+      } else if (e <= 0) { // Underflow
+        if (e < -10) {
+          // The absolute fp32 value is less than MIN_VALUE, flush to +/-0
+        } else {
+          // The fp32 value is a normalized float less than MIN_NORMAL,
+          // we convert to a denorm fp16
+          m = m | 0x800000;
+          int shift = 14 - e;
+          outM = m >> shift;
+          int lowm = m & ((1 << shift) - 1);
+          int hway = 1 << (shift - 1);
+          // if above halfway or exactly halfway and outM is odd
+          if (lowm + (outM & 1) > hway) {
+            // Round to nearest even
+            // Can overflow into exponent bit, which surprisingly is OK.
+            // This increment relies on the +outM in the return statement below
+            outM++;
+          }
+        }
+      } else {
+        outE = e;
+        outM = m >> 13;
+        // if above halfway or exactly halfway and outM is odd
+        if ((m & 0x1fff) + (outM & 0x1) > 0x1000) {
+          // Round to nearest even
+          // Can overflow into exponent bit, which surprisingly is OK.
+          // This increment relies on the +outM in the return statement below
+          outM++;
+        }
+      }
+    }
+    // The outM is added here as the +1 increments for outM above can
+    // cause an overflow in the exponent bit which is OK.
+    return (short) ((s << SIGN_SHIFT) | (outE << EXPONENT_SHIFT) + outM);
+  }
+
+  /**
+   * Returns a string representation of the specified half-precision
+   * float value. Calling this method is equivalent to calling
+   * <code>Float.toString(toFloat(h))</code>. See {@link Float#toString(float)}
+   * for more information on the format of the string representation.
+   *
+   * @param h A half-precision float value in binary little-endian format
+   * @return A string representation of the specified value
+   */
+  @VisibleForTesting
+  public static String toFloatString(short h) {
+    return Float.toString(Float16.toFloat(h));
+  }
+}

java/memory/memory-core/src/test/java/org/apache/arrow/memory/TestArrowBuf.java

@@ -29,6 +29,7 @@
 import java.nio.ByteOrder;
 import java.util.Arrays;
 
+import org.apache.arrow.memory.util.Float16;
 import org.junit.Test;
 import org.slf4j.LoggerFactory;
 
@@ -180,4 +181,15 @@ public void testEnabledHistoricalLog() {
       ((Logger) LoggerFactory.getLogger("org.apache.arrow")).setLevel(null);
     }
   }
+
+  @Test
+  public void testArrowBufFloat16() {
+    try (BufferAllocator allocator = new RootAllocator();
+         ArrowBuf buf = allocator.buffer(1024)
+    ) {
+      buf.setFloat16(0, +32.875f);
+      assertEquals((short) 0x501c, Float16.toFloat16(+32.875f));
+      assertEquals((short) 0x501c, buf.getFloat16(0));
+    }
+  }
 }

java/vector/src/main/codegen/data/ValueVectorTypes.tdd

@@ -48,6 +48,15 @@
       minor: [
         { class: "SmallInt", valueHolder: "Int2Holder"},
       ]
+    },    {
+      major: "Fixed",
+      width: 2,
+      javaType: "short",
+      boxedType: "Short",
+      fields: [{name: "value", type: "short"}],
+      minor: [
+        { class: "Float2", valueHolder: "Int2Holder"},
+      ]
     },
     {
       major: "Fixed",

java/vector/src/main/codegen/templates/UnionReader.java

@@ -39,7 +39,7 @@
 @SuppressWarnings("unused")
 public class UnionReader extends AbstractFieldReader {
 
-  private BaseReader[] readers = new BaseReader[45];
+  private BaseReader[] readers = new BaseReader[46];
   public UnionVector data;
 
   public UnionReader(UnionVector data) {
@@ -50,7 +50,7 @@ public MinorType getMinorType() {
     return TYPES[data.getTypeValue(idx())];
   }
 
-  private static MinorType[] TYPES = new MinorType[45];
+  private static MinorType[] TYPES = new MinorType[46];
 
   static {
     for (MinorType minorType : MinorType.values()) {