| /*first level: one 16 samples butterfly*/ |
| /*(s0 ÷ s7)+(s8 ÷ s15)*/ |
| vaddh out_low = in_low, in_high |
| /*(s0 ÷ s7)−(s8 ÷ s15)*/ |
| vsubh out_high = in_low, in_high |
|
| /*data reordering*/ |
| /*0 1 2 3 8 9 10 11*/ |
| vmrgbl in_low = out_low, out_high, perm |
| /*4 5 6 7 12 13 14 15*/ |
| vmrgbu in_high = out_low, out_high, perm |
|
| /*second level: two 8 samples butterfly*/ |
| vaddh out_low = in_low, in_high |
| vsubh out_high = in_low, in_high |
|
| /*data reordering*/ |
| /*0 1 8 9 4 5 12 13*/ |
| vmrge in_low = out_low, out_high |
| /*2 3 10 11 6 7 14 15*/ |
| vmrgo in_high = out_low, out_high |
|
| /*third level: four 4 samples butterfly*/ |
| vaddh out_low = in_low, in_high |
| vsubh out_high = in_low, in_high |
|
| /*data reordering*/ |
| /*0 8 2 10 4 12 6 14*/ |
| vmrgeh in_low = out_low, out_high |
| /*1 9 3 11 5 13 7 15*/ |
| vmrgoh in_high = out_low, out_high |
|
| /*fourth level: eight 2 samples butterfly*/ |
| vaddh out_low = in_low, in_high |
| vsubh out_high = in_low, in_high |
