* psrc / pdst - predicate mask selector and inversion
* vspec - 3 bit src / dest scalar-vector extension
+# standard arith ops (single predication)
+
+these are of the form res = op(src1, src2, ...)
+
+| 0 1 | 2 3 | 5 | 6 8 | 13 20 |
+| ----- | --- | ---- | ---- | ----- |
+| subvl | ew | ptyp | pred | vspec |
+
+
+* subvl - 1 to 4 scalar / vec2 / vec3 / vec4
+* ew - DEFAULT / 8 / 16 /32 element width
+* ptyp - predication INT / CR
+* pred - predicate mask selector and inversion
+* vspec - 2/3 bit src / dest scalar-vector extension
+
+For 2 op (dest/src1/src2) the tag may be 2 bits. for 3 op (dest/src1/2/3) the vspec may be 2 bits per reg.
# Notes about Swizzle