src/ieee754/part_cmp/experiments/equal_ortree.py

   1 # SPDX-License-Identifier: LGPL-2.1-or-later
   2 # See Notices.txt for copyright information
   3
   4 """
   5 Copyright (C) 2020 Luke Kenneth Casson Leighton <lkcl@lkcl.net>
   6
   7 dynamically-partitionable "comparison" class, directly equivalent
   8 to Signal.__eq__ except SIMD-partitionable
   9
  10 See:
  11
  12 * http://libre-riscv.org/3d_gpu/architecture/dynamic_simd/eq
  13 * http://bugs.libre-riscv.org/show_bug.cgi?id=132
  14 """
  15
  16 from nmigen import Signal, Module, Elaboratable, Cat, C, Mux, Repl
  17 from nmigen.cli import main
  18
  19 from ieee754.part_mul_add.partpoints import PartitionPoints
  20 from ieee754.part_cmp.experiments.eq_combiner import EQCombiner
  21
  22
  23 class PartitionedEq(Elaboratable):
  24
  25     def __init__(self, width, partition_points):
  26         """Create a ``PartitionedEq`` operator
  27         """
  28         self.width = width
  29         self.a = Signal(width, reset_less=True)
  30         self.b = Signal(width, reset_less=True)
  31         self.partition_points = PartitionPoints(partition_points)
  32         self.mwidth = len(self.partition_points)+1
  33         self.output = Signal(self.mwidth, reset_less=True)
  34         if not self.partition_points.fits_in_width(width):
  35             raise ValueError("partition_points doesn't fit in width")
  36
  37     def elaborate(self, platform):
  38         m = Module()
  39         comb = m.d.comb
  40         m.submodules.eqc = eqc = EQCombiner(self.mwidth)
  41
  42         # make a series of "not-eqs", splitting a and b into partition chunks
  43         nes = Signal(self.mwidth, reset_less=True)
  44         nel = []
  45         keys = list(self.partition_points.keys()) + [self.width]
  46         start = 0
  47         for i in range(len(keys)):
  48             end = keys[i]
  49             nel.append(self.a[start:end] != self.b[start:end])
  50             start = end # for next time round loop
  51         comb += nes.eq(Cat(*nel))
  52
  53         comb += eqc.gates.eq(self.partition_points.as_sig())
  54         comb += eqc.neqs.eq(nes)
  55         comb += self.output.eq(eqc.outputs)
  56
  57
  58         return m