VectorMask.firstTrue()/lastTrue()

[Remi Forax]

There is a way to implement firstTrue and lastTrue using only vector operations.

The idea is to use to mask iota with the mask and then do a reduceLanes with MIN or MAX.
By example to for firstTrue() that returns -1 if the mask is empty,
first create iotaPlusOne, blend with zero, then reduceLanes with MIN, then substract 1

  VectorMask mask = ...
  var iotaPlusOne = ByteVector.broadcast(SPECIES, 1).addIndex(1);
  ByteVector.zero(SPECIES).blend(iotaPlusOne, mask).reduceLanes(VectorOperators.MIN) - 1;

BTW, i wonder why firstTrue return the mask length instead of -1.

regards,
Rémi