Ah I see now! Thank you for explaining that bit, I was a bit puzzled when I saw
it, but it makes sense now!
Cheers, Alan
Bill Schmidt wrote:
On Thu, 2014-11-06 at 16:44 +0000, Alan Lawrence wrote:
Hmmm. I am a little surprised by your mention of "saturation points" as I would
not expect any variety of reduc_plus to be a saturating operation???
I wouldn't either, but the underlying vsum4ubs and vsum4sbs instructions
used in these patterns do both a reduction and an add to another value.
If that other value is large enough this can trigger a saturation event.
However, the patterns use vzero for this other value, so it's not
possible to approach the saturation cutoff for either instruction since
the reductions are being done on byte values. (Each word in the vector
result is the sum of the corresponding four byte values in the vector
source, added to the other value, which here is zero.)
Thanks,
Bill
