src/ieee754/fsgnj/fsgnj.py

   1 # IEEE Floating Point Conversion, FSGNJ
   2 # Copyright (C) 2019 Luke Kenneth Casson Leighton <lkcl@lkcl.net>
   3 # Copyright (C) 2020 Michael Nolan <mtnolan2640@gmail.com>
   4
   5
   6 from nmigen import Module, Signal, Cat, Mux
   7
   8 from nmutil.pipemodbase import PipeModBase
   9 from ieee754.fpcommon.basedata import FPBaseData
  10 from ieee754.fpcommon.packdata import FPPackData
  11 from ieee754.fpcommon.fpbase import FPNumDecode, FPNumBaseRecord
  12
  13
  14 class FSGNJPipeMod(PipeModBase):
  15     """ FP Sign injection - replaces operand A's sign bit with one
  16         generated from operand B
  17
  18         self.ctx.i.op & 0x3 == 0x0 : Copy sign bit from operand B
  19         self.ctx.i.op & 0x3 == 0x1 : Copy inverted sign bit from operand B
  20         self.ctx.i.op & 0x3 == 0x2 : Sign bit is A's sign XOR B's sign
  21     """
  22     def __init__(self, in_pspec):
  23         self.in_pspec = in_pspec
  24         super().__init__(in_pspec, "fsgnj")
  25
  26     def ispec(self):
  27         return FPBaseData(self.in_pspec)
  28
  29     def ospec(self):
  30         return FPPackData(self.in_pspec)
  31
  32     def elaborate(self, platform):
  33         m = Module()
  34
  35         width = self.pspec.width
  36         comb = m.d.comb
  37
  38         z1 = self.o.z
  39         a = self.i.a
  40         b = self.i.b
  41         a1 = FPNumBaseRecord(width, False)
  42         b1 = FPNumBaseRecord(width, False)
  43         m.submodules.sc_decode_a = a1 = FPNumDecode(None, a1)
  44         m.submodules.sc_decode_b = b1 = FPNumDecode(None, b1)
  45         comb += [a1.v.eq(self.i.a),
  46                  b1.v.eq(self.i.b)]
  47
  48         opcode = self.i.ctx.op
  49
  50         sign = Signal()
  51
  52         sign = Mux(opcode[0], ~b1.s, b1.s)
  53         sign = Mux(opcode[1], sign ^ a1.s, sign)
  54
  55
  56         comb += z1.eq(a1.fp.create2(sign, a1.e, a1.m))
  57
  58         # copy the context (muxid, operator)
  59         comb += self.o.ctx.eq(self.i.ctx)
  60
  61         return m