# permute.py
from myhdl import always_comb, intbv

def permute(a, x, mapping):
      a: input signal
      x: output signal
      mapping: specifies which bit of a drives each bit of x.
        that is: x[i] = a[mapping[i]]
      a and x must be the same width
      the length of mapping equals the signal width

  def logic():
    for i in mapping:
      x.next[i] = a[mapping[i]]

  return logic