src/soc/fu/shift_rot/rotl.py

   1 from nmigen import (Elaboratable, Signal, Module, Cat)
   2 import math
   3
   4 class ROTL(Elaboratable):
   5     def __init__(self, width):
   6         self.width = width
   7         self.shiftwidth = math.ceil(math.log2(width))
   8         self.a = Signal(width, reset_less=True)
   9         self.b = Signal(self.shiftwidth, reset_less=True)
  10
  11         self.o = Signal(width, reset_less=True)
  12
  13     def elaborate(self, platform):
  14         m = Module()
  15         comb = m.d.comb
  16         # trick to do double-concatenation of a then left shift.
  17         # synth tools know to turn this pattern into a barrel-shifter
  18         comb += self.o.eq(Cat(self.a, self.a).bit_select(self.width - self.b,
  19                                                          len(self.a)))
  20         return m