impl q14x2 ops in interpreter

These tests cover all the new Q14x2 ops.
As usual, left myself a few TODOs...

While working on this, I uncovered a little subtly about the blend
instructions we use to implement Op::select... unlike the platonic

    (cond & true_val) | (~cond & false_val)

the hardware istructions are not bitwise!  Each of the fancy blend
instructions like vblendvps or vpblendvb has a fundamental granularity
larger than a bit (4 bytes for vblendvps, 1 byte for vpblendvb).  If
you're using a mask with a granularity of say, 2 bytes, you need to be
using something with equally fine granularity --- bitwise is ok,
bytewise is ok, 2-byte-wise is ok, but 4-byte-wise isn't.

Took a quick survey, and the Op::select we're using for x86 and ARM
JITs are both bytewise, so I think they're fine.  Would have to think
a bit about LLVM, but these unit tests should at least fire if it were
wrong.  The skvx if_then_else() I've been using in the interpreter has
been 4-byte-wise, but I'm refining that down to 1-byte-wise with

Change-Id: I09cbc8b91cdb9e50088ee4f6ddf202faa1bf2cb1
Reviewed-by: Herb Derby <>
Commit-Queue: Mike Klein <>
3 files changed