shubhamvishu commented on code in PR #12868:
URL: https://github.com/apache/lucene/pull/12868#discussion_r1756832910
##########
lucene/core/src/java/org/apache/lucene/util/StringHelper.java:
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@@ -209,6 +209,156 @@ public static int murmurhash3_x86_32(BytesRef bytes, int
seed) {
return murmurhash3_x86_32(bytes.bytes, bytes.offset, bytes.length, seed);
}
+ /**
+ * Generates 128-bit hash from the byte array with the given offset, length
and seed.
+ *
+ * <p>The code is adopted from Apache Commons (<a
+ *
href="https://commons.apache.org/proper/commons-codec/jacoco/org.apache.commons.codec.digest/MurmurHash3.java.html";>link</a>)
+ *
+ * @param data The input byte array
+ * @param offset The first element of array
+ * @param length The length of array
+ * @param seed The initial seed value
+ * @return The 128-bit hash (2 longs)
+ */
+ public static long[] murmurhash3_x64_128(
+ final byte[] data, final int offset, final int length, final int seed) {
+ // Use an unsigned 32-bit integer as the seed
+ return murmurhash3_x64_128(data, offset, length, seed & 0xFFFFFFFFL);
+ }
+
+ @SuppressWarnings("fallthrough")
+ private static long[] murmurhash3_x64_128(
+ final byte[] data, final int offset, final int length, final long seed) {
+ long h1 = seed;
+ long h2 = seed;
+ final int nblocks = length >> 4;
+
+ // Constants for 128-bit variant
+ final long C1 = 0x87c37b91114253d5L;
+ final long C2 = 0x4cf5ad432745937fL;
+ final int R1 = 31;
+ final int R2 = 27;
+ final int R3 = 33;
+ final int M = 5;
+ final int N1 = 0x52dce729;
+ final int N2 = 0x38495ab5;
+
+ // body
+ for (int i = 0; i < nblocks; i++) {
+ final int index = offset + (i << 4);
+ long k1 = (long) BitUtil.VH_LE_LONG.get(data, index);
+ long k2 = (long) BitUtil.VH_LE_LONG.get(data, index + 8);
+
+ // mix functions for k1
+ k1 *= C1;
+ k1 = Long.rotateLeft(k1, R1);
+ k1 *= C2;
+ h1 ^= k1;
+ h1 = Long.rotateLeft(h1, R2);
+ h1 += h2;
+ h1 = h1 * M + N1;
+
+ // mix functions for k2
+ k2 *= C2;
+ k2 = Long.rotateLeft(k2, R3);
+ k2 *= C1;
+ h2 ^= k2;
+ h2 = Long.rotateLeft(h2, R1);
+ h2 += h1;
+ h2 = h2 * M + N2;
+ }
+
+ // tail
+ long k1 = 0;
+ long k2 = 0;
+ final int index = offset + (nblocks << 4);
+ switch (offset + length - index) {
Review Comment:
Makes sense. I'll update it (Maybe we could do this in the [Apache commons
impl](https://github.com/apache/commons-codec/blob/master/src/main/java/org/apache/commons/codec/digest/MurmurHash3.java)
also)
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