srowen commented on a change in pull request #32822:
URL: https://github.com/apache/spark/pull/32822#discussion_r649087032
##########
File path: mllib-local/src/main/scala/org/apache/spark/ml/impl/Utils.scala
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@@ -94,4 +95,43 @@ private[spark] object Utils {
math.log1p(math.exp(x))
}
}
+
+ /**
+ * Perform in-place softmax conversion.
+ */
+ def softmax(values: Array[Double]): Unit = {
+ var maxValue = Double.MinValue
+ var i = 0
+ while (i < values.length) {
+ val value = values(i)
+ if (value.isPosInfinity) {
+ java.util.Arrays.fill(values, 0)
+ values(i) = 1.0
+ return
+ } else if (value > maxValue) {
+ maxValue = value
+ }
+ i += 1
+ }
+
+ var sum = 0.0
+ i = 0
+ if (maxValue > 0) {
Review comment:
Hm, would this not be valuable even if the max were very small? avoids
underflow in exp in the same way it avoids overflow when the max is large. This
avoids two branches
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