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, 2))  # append pair, max_value
  28         return pairs
  29
  30     def combine_pairs(self, m, iteration, pairs):
  31         comb = m.d.comb
  32         length = len(pairs)
  33         ret = []
  34         for i in range(0, length, 2):
  35             if i+1 >= length:
  36                 right, mv = pairs[i]
  37                 width = right.width
  38                 print(f"single({i}) - cnt_{iteration}_{i}")
  39                 new_pair = Signal(width, name="cnt_%d_%d" % (iteration, i))
  40                 comb += new_pair.eq(Cat(right, 0))
  41                 ret.append((new_pair, mv))
  42             else:
  43                 left, lv = pairs[i+1]
  44                 right, rv = pairs[i]
  45                 width = right.width + 1
  46                 print(left)
  47                 print(f"pair({left}, {right}) - cnt_{iteration}_{i}")
  48                 new_pair = Signal(width, name="cnt_%d_%d" %
  49                                   (iteration, i))
  50                 if rv == lv:
  51                     with m.If(left[-1] == 1):
  52                         with m.If(right[-1] == 1):
  53                             comb += new_pair.eq(Cat(Repl(0, width-1), 1))
  54                         with m.Else():
  55                             comb += new_pair.eq(Cat(right[0:-1], 0b01))
  56                     with m.Else():
  57                         comb += new_pair.eq(Cat(left, 0))
  58                 else:
  59                     with m.If(left == lv):
  60                         comb += new_pair.eq(right + left)
  61                     with m.Else():
  62                         comb += new_pair.eq(left)
  63
  64
  65                 ret.append((new_pair, lv+rv))
  66         return ret
  67
  68     def elaborate(self, platform):
  69         m = Module()
  70         comb = m.d.comb
  71
  72         pairs = self.generate_pairs(m)
  73         i = 2
  74         while len(pairs) > 1:
  75             pairs = self.combine_pairs(m, i, pairs)
  76             print(pairs)
  77             i += 1
  78
  79         comb += self.lz.eq(pairs[0][0])
  80
  81         return m
  82
  83