src/ieee754/fpcmp/fpcmp.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, 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 FPCMPPipeMod(PipeModBase):
  15     """
  16     Floating point comparison: FEQ, FLT, FLE
  17     Opcodes (funct3):
  18        - 0b00 - FLE - floating point less than or equal to
  19        - 0b01 - FLT - floating point less than
  20        - 0b10 - FEQ - floating equals
  21     """
  22     def __init__(self, in_pspec):
  23         self.in_pspec = in_pspec
  24         super().__init__(in_pspec, "fpcmp")
  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         # useful clarity variables
  36         comb = m.d.comb
  37         width = self.pspec.width
  38         opcode = self.i.ctx.op
  39         z1 = self.o.z
  40
  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
  46         m.d.comb += [a1.v.eq(self.i.a),
  47                      b1.v.eq(self.i.b)]
  48
  49         both_zero = Signal()
  50         comb += both_zero.eq((a1.v[0:width-1] == 0) &
  51                              (b1.v[0:width-1] == 0))
  52
  53         ab_equal = Signal()
  54         m.d.comb += ab_equal.eq((a1.v == b1.v) | both_zero)
  55
  56         contains_nan = Signal()
  57         m.d.comb += contains_nan.eq(a1.is_nan | b1.is_nan)
  58         a_lt_b = Signal()
  59
  60         # if(a1.is_zero && b1.is_zero):
  61         #    a_lt_b = 0
  62         # elif(a1.s != b1.s):
  63         #    a_lt_b = a1.s > b1.s (a is more negative than b)
  64         signs_same = Signal()
  65         comb += signs_same.eq(a1.s > b1.s)
  66
  67         # else:  # a1.s == b1.s
  68         #    if(a1.s == 0):
  69         #         a_lt_b = a[0:31] < b[0:31]
  70         #    else:
  71         #         a_lt_b = a[0:31] > b[0:31]
  72         signs_different = Signal()
  73         comb += signs_different.eq(Mux(a1.s,
  74                                        (a1.v[0:width-1] > b1.v[0:width-1]),
  75                                        (a1.v[0:width-1] < b1.v[0:width-1])))
  76
  77         comb += a_lt_b.eq(Mux(both_zero, 0,
  78                               Mux(a1.s == b1.s,
  79                               signs_different,
  80                               signs_same)))
  81
  82         no_nan = Signal()
  83         # switch(opcode):
  84         #   case(0b00): # lt
  85         #       no_nan = a_lt_b
  86         #   case(0b01): # le
  87         #       no_nan = ab_equal
  88         #   case(0b10):
  89         #       no_nan = a_lt_b | ab_equal
  90         comb += no_nan.eq(
  91             Mux(opcode != 0b00, ab_equal, 0) |
  92             Mux(opcode[1], 0, a_lt_b))
  93
  94         # if(a1.is_nan | b1.is_nan):
  95         #    z1 = 0
  96         # else:
  97         #    z1 = no_nan
  98         comb += z1.eq(Mux(contains_nan, 0, no_nan))
  99
 100         # copy the context (muxid, operator)
 101         comb += self.o.ctx.eq(self.i.ctx)
 102
 103         return m