openpower/sv/mv.swizzle.mdwn

   1 # mv.swizzle
   2
   3 TODO: evaluate whether this will fit with [[mv.vec]]
   4
   5 # Format
   6
   7 | 0..5 |6..10|11..15|16.20|21.....25|26.....30|31|  name    |
   8 |------|-----|------|-----|---------|---------|--|----------|
   9 | 19   | RT  | RA   |     | XO[0:4] | XO[5:9] |Rc| XL-Form  |
  10 | 19   | RT  | RA   |imm  | imm     | iNNNN   |im| mv.swiz  |
  11 | 19   | RT  | RA   |imm  | imm     | iNNNN   |im| fmv.swiz |
  12
  13 also f.mv
  14
  15 this gives an 11 bit immediate across bits 16 to 26 and bit 31.  a permutation based encoding should allow the 12 bits to be covered
  16
  17 * 3 bits X
  18 * 3 bits Y
  19 * 3 bits Z
  20 * 3 bits W
  21
  22 except that the options are:
  23
  24 * 0b1NN index 0 thru 3 to place subelement in pos XYZW
  25 * 0b000 to indicate "skip"
  26 * 0b001 to indicate "constant 0"
  27 * 0b010 to indicate "constant 1" (or 1.0)
  28 * 0b011 is not needed.
  29
  30 Evaluating efforts to encode 12 bit swizzle into less proved unsuccessful: 7^4 wcomes out to 2,400 which is larger than 11 bits