src/ieee754/cordic/clz.py

   1 from nmigen import Module, Signal, Elaboratable, Cat, Repl
   2 import math
   3
   4 class CLZ(Elaboratable):
   5     def __init__(self, width):
   6         self.width = width
   7         self.sig_in = Signal(width, reset_less=True)
   8         out_width = math.ceil(math.log2(width+1))
   9         self.lz = Signal(out_width)
  10
  11     def generate_pairs(self, m):
  12         comb = m.d.comb
  13         assert self.width % 2 == 0  # TODO handle odd widths
  14         pairs = []
  15         for i in range(0, self.width, 2):
  16             pair = Signal(2, name="pair%d" % i)
  17             comb += pair.eq(self.sig_in[i:i+2])
  18
  19             pair_cnt = Signal(2, name="cnt_1_%d" % (i/2))
  20             with m.Switch(pair):
  21                 with m.Case(0):
  22                     comb += pair_cnt.eq(2)
  23                 with m.Case(1):
  24                     comb += pair_cnt.eq(1)
  25                 with m.Default():
  26                     comb += pair_cnt.eq(0)
  27             pairs.append(pair_cnt)
  28         return pairs
  29
  30     def combine_pairs(self, m, iteration, pairs):
  31         comb = m.d.comb
  32         length = len(pairs)
  33         assert length % 2 == 0  # TODO handle non powers of 2
  34         ret = []
  35         for i in range(0, length, 2):
  36             left = pairs[i+1]
  37             right = pairs[i]
  38             width = left.width + 1
  39             print(left)
  40             print(f"pair({i}, {i+1}) - cnt_{iteration}_{i}")
  41             new_pair = Signal(left.width + 1, name="cnt_%d_%d" %
  42                               (iteration, i))
  43             with m.If(left[-1] == 1):
  44                 with m.If(right[-1] == 1):
  45                     comb += new_pair.eq(Cat(Repl(0, width-1), 1))
  46                 with m.Else():
  47                     comb += new_pair.eq(Cat(right[0:-1], 0b01))
  48             with m.Else():
  49                 comb += new_pair.eq(Cat(left, 0))
  50
  51             ret.append(new_pair)
  52         return ret
  53
  54     def elaborate(self, platform):
  55         m = Module()
  56         comb = m.d.comb
  57
  58         pairs = self.generate_pairs(m)
  59         i = 2
  60         while len(pairs) > 1:
  61             pairs = self.combine_pairs(m, i, pairs)
  62             i += 1
  63
  64         comb += self.lz.eq(pairs[0])
  65
  66         return m
  67
  68