+[[!tag standards]]
+
# mv.swizzle
-# Format
+Links
-| 0..5 |6..10|11..15|16.20|21.....25|26.....30|31| name |
-|------|-----|------|-----|---------|---------|--|---------|
-| 19 | RT | RA | | XO[0:4] | XO[5:9] |Rc| XL-Form |
-| 19 | RT | RA |imm | imm | Nn NNN |im| mv.swiz |
+* <https://bugs.libre-soc.org/show_bug.cgi?id=139>
-also f.mv
+TODO: evaluate whether this will fit with [[mv.vec]]
-this gives an 11 bit immediate across bits 16 to 25 and bit 31. a permutation based encoding should allow the 12 bits to be covered
+the encoding embeds predication into the swizzle as well as constants 1/1.0 and 0/0.0
+
+# Format
+
+| 0.5 |6.10|11.15|16.20|21.....25|26.....30|31| name |
+|-----|----|-----|-----|---------|---------|--|--------------|
+| 19 | RT | RA | | XO[0:4] | XO[5:9] |Rc| XL-Form |
+| 19 | RT | RA |imm | imm | 01 M im |0 | mv.vec.swiz |
+| 19 | RT | RA |imm | imm | 01 M im |1 | fmv.vec.swiz |
+| 19 | RT | RA |imm | imm | 11 0 im |0 | mv.swiz |
+| 19 | RT | RA |imm | imm | 11 0 im |1 | fmv.swiz |
+
+this gives a 12 bit immediate across bits 16 to 25 and 29-30.
* 3 bits X
* 3 bits Y
except that the options are:
-* 0b1NN index 0 thru 3 to place subelement in pos XYZW
-* 0b000 to indicate "skip"
-* 0b001 to indicate "constant 0"
-* 0b010 to indicate "constant 1" (or 1.0)
-* 0b011 is not needed.
+* 0b0NN index 0 thru 3 to place subelement in pos XYZW
+* 0b110 to indicate "skip". this is equivalent to predicate masking
+* 0b100 to indicate "constant 0"
+* 0b101 to indicate "constant 1" (or 1.0)
+* 0b111 is not needed.
+
+Evaluating efforts to encode 12 bit swizzle into less proved unsuccessful: 7^4 comes out to 2,400 which is larger than 11 bits.
-this "not needed" means the encoding is actually a lot less. the sequences involve expressing how many 0s and 1s are embedded in amongst the XYZWs which gets really interesting.
+Note that 7 options are needed (not 6) because the 7th option allows predicate masking to be encoded within the swizzle immediate.
+Mode M is described in [[mv.vec]] and allows for merge and split of vectors.