src/ieee754/fpadd/add0.py

   1 """IEEE754 Floating Point Adder Pipeline
   2
   3 Copyright (C) 2019 Luke Kenneth Casson Leighton <lkcl@lkcl.net>
   4
   5 """
   6
   7 from nmigen import Module, Signal, Cat, Mux
   8 from nmigen.cli import main, verilog
   9
  10 from nmutil.pipemodbase import PipeModBase
  11
  12 from ieee754.fpcommon.denorm import FPSCData
  13 from ieee754.fpcommon.getop import FPPipeContext
  14 from ieee754.fpadd.datastruct import FPAddStage0Data
  15
  16
  17 class FPAddStage0Mod(PipeModBase):
  18
  19     def __init__(self, pspec):
  20         super().__init__(pspec, "add0")
  21
  22     def ispec(self):
  23         return FPSCData(self.pspec, True)
  24
  25     def ospec(self):
  26         return FPAddStage0Data(self.pspec)
  27
  28     def elaborate(self, platform):
  29         m = Module()
  30         comb = m.d.comb
  31
  32         # store intermediate tests (and zero-extended mantissas)
  33         seq = Signal(reset_less=True)
  34         mge = Signal(reset_less=True)
  35         am0 = Signal(len(self.i.a.m)+1, reset_less=True)
  36         bm0 = Signal(len(self.i.b.m)+1, reset_less=True)
  37         # same-sign (both negative or both positive) add mantissas
  38         comb += [seq.eq(self.i.a.s == self.i.b.s),
  39                  mge.eq(self.i.a.m >= self.i.b.m),
  40                  am0.eq(Cat(self.i.a.m, 0)),
  41                  bm0.eq(Cat(self.i.b.m, 0))
  42                 ]
  43         comb += self.o.z.e.eq(self.i.a.e)
  44         comb += self.o.z.s.eq(Mux(seq | mge, self.i.a.s, self.i.b.s))
  45         with m.If(seq):
  46             comb += [
  47                 self.o.tot.eq(am0 + bm0),
  48             ]
  49         # a mantissa greater than b, use a
  50         with m.Elif(mge):
  51             comb += [
  52                 self.o.tot.eq(am0 - bm0),
  53             ]
  54         # b mantissa greater than a, use b
  55         with m.Else():
  56             comb += [
  57                 self.o.tot.eq(bm0 - am0),
  58         ]
  59
  60         # pass-through context
  61         comb += self.o.oz.eq(self.i.oz)
  62         comb += self.o.out_do_z.eq(self.i.out_do_z)
  63         comb += self.o.ctx.eq(self.i.ctx)
  64
  65         return m