Github user srowen commented on a diff in the pull request:
https://github.com/apache/spark/pull/8314#discussion_r42936325
--- Diff:
core/src/main/scala/org/apache/spark/util/random/XORShiftRandom.scala ---
@@ -60,9 +60,11 @@ private[spark] class XORShiftRandom(init: Long) extends
JavaRandom(init) {
private[spark] object XORShiftRandom {
/** Hash seeds to have 0/1 bits throughout. */
- private def hashSeed(seed: Long): Long = {
+ private[random] def hashSeed(seed: Long): Long = {
val bytes =
ByteBuffer.allocate(java.lang.Long.SIZE).putLong(seed).array()
- MurmurHash3.bytesHash(bytes)
+ val lowBits = MurmurHash3.bytesHash(bytes)
+ val highBits = MurmurHash3.bytesHash(bytes, lowBits)
+ (highBits.toLong << 32) | (lowBits.toLong & 0xFFFFFFFFL)
--- End diff --
Although normally it might not be 100% valid to make a 64-bit hash out of
two 32-bit hashes this way (I'm not clear that reusing the seed doesn't connect
the bits in some subtle way), it's certainly a big improvement and probably
entirely fine for this purpose. I'd still like to remove XORShiftRandom, but
that can be for another day.
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