RFR: 8338023: Support two vector selectFrom API [v5]

[John Rose]

On 23 Aug 2024, at 15:33, Paul Sandoz wrote:

> The float/double conversion bothers me, not suggesting we do something about it here, noting down for any future conversation on shuffles.

Yes, it’s a pain which is noticeable in the vector/shuffle conversions.
In the worst case it adds dynamic reformatting operations to get from
the artificially “uniform” float/double index format into the real
format the hardware requires.  As a workaround, the user could convert
the float/double payloads bitwise into int/long payloads, and then
do the shuffling in the uniform int/long API, later reconverting
back to float/double after the payloads are reordered.  Those
conversions don’t actually use any dynamic operations.

For prototyping, it seems fine to take the hit and ignore the fact
that the index vectors are in an odd (though “uniform”) format.