src/ieee754/fpdiv/specialcases.py

   1 # IEEE Floating Point Multiplier
   2
   3 from nmigen import Module, Signal, Cat, Const, Elaboratable
   4 from nmigen.cli import main, verilog
   5 from math import log
   6
   7 from ieee754.fpcommon.fpbase import FPNumDecode, FPNumBaseRecord
   8 from nmutil.singlepipe import SimpleHandshake, StageChain
   9
  10 from ieee754.fpcommon.fpbase import FPState, FPID
  11 from ieee754.fpcommon.getop import FPADDBaseData
  12 from ieee754.fpcommon.denorm import (FPSCData, FPAddDeNormMod)
  13
  14
  15 class FPDIVSpecialCasesMod(Elaboratable):
  16     """ special cases: NaNs, infs, zeros, denormalised
  17         see "Special Operations"
  18         https://steve.hollasch.net/cgindex/coding/ieeefloat.html
  19     """
  20
  21     def __init__(self, pspec):
  22         self.pspec = pspec
  23         self.i = self.ispec()
  24         self.o = self.ospec()
  25
  26     def ispec(self):
  27         return FPADDBaseData(self.pspec)
  28
  29     def ospec(self):
  30         return FPSCData(self.pspec, False)
  31
  32     def setup(self, m, i):
  33         """ links module to inputs and outputs
  34         """
  35         m.submodules.specialcases = self
  36         m.d.comb += self.i.eq(i)
  37
  38     def process(self, i):
  39         return self.o
  40
  41     def elaborate(self, platform):
  42         m = Module()
  43
  44         #m.submodules.sc_out_z = self.o.z
  45
  46         # decode: XXX really should move to separate stage
  47         a1 = FPNumBaseRecord(self.pspec.width, False)
  48         b1 = FPNumBaseRecord(self.pspec.width, False)
  49         m.submodules.sc_decode_a = a1 = FPNumDecode(None, a1)
  50         m.submodules.sc_decode_b = b1 = FPNumDecode(None, b1)
  51         m.d.comb += [a1.v.eq(self.i.a),
  52                      b1.v.eq(self.i.b),
  53                      self.o.a.eq(a1),
  54                      self.o.b.eq(b1)
  55                     ]
  56
  57         sabx = Signal(reset_less=True)   # sign a xor b (sabx, get it?)
  58         m.d.comb += sabx.eq(a1.s ^ b1.s)
  59
  60         abnan = Signal(reset_less=True)
  61         m.d.comb += abnan.eq(a1.is_nan | b1.is_nan)
  62
  63         abinf = Signal(reset_less=True)
  64         m.d.comb += abinf.eq(a1.is_inf & b1.is_inf)
  65
  66         # if a is NaN or b is NaN return NaN
  67         with m.If(abnan):
  68             m.d.comb += self.o.out_do_z.eq(1)
  69             m.d.comb += self.o.z.nan(1)
  70
  71         # if a is inf and b is Inf return NaN
  72         with m.Elif(abnan):
  73             m.d.comb += self.o.out_do_z.eq(1)
  74             m.d.comb += self.o.z.nan(1)
  75
  76         # if a is inf return inf
  77         with m.Elif(a1.is_inf):
  78             m.d.comb += self.o.out_do_z.eq(1)
  79             m.d.comb += self.o.z.inf(sabx)
  80
  81         # if b is inf return zero
  82         with m.Elif(b1.is_inf):
  83             m.d.comb += self.o.out_do_z.eq(1)
  84             m.d.comb += self.o.z.zero(sabx)
  85
  86         # if a is zero return zero (or NaN if b is zero)
  87         with m.Elif(a1.is_zero):
  88             m.d.comb += self.o.out_do_z.eq(1)
  89             m.d.comb += self.o.z.zero(sabx)
  90             # b is zero return NaN
  91             with m.If(b1.is_zero):
  92                 m.d.comb += self.o.z.nan(1)
  93
  94         # if b is zero return Inf
  95         with m.Elif(b1.is_zero):
  96             m.d.comb += self.o.out_do_z.eq(1)
  97             m.d.comb += self.o.z.inf(sabx)
  98
  99         # Denormalised Number checks next, so pass a/b data through
 100         with m.Else():
 101             m.d.comb += self.o.out_do_z.eq(0)
 102
 103         m.d.comb += self.o.oz.eq(self.o.z.v)
 104         m.d.comb += self.o.mid.eq(self.i.mid)
 105
 106         return m
 107
 108
 109 class FPDIVSpecialCases(FPState):
 110     """ special cases: NaNs, infs, zeros, denormalised
 111         NOTE: some of these are unique to div.  see "Special Operations"
 112         https://steve.hollasch.net/cgindex/coding/ieeefloat.html
 113     """
 114
 115     def __init__(self, pspec):
 116         FPState.__init__(self, "special_cases")
 117         self.mod = FPDIVSpecialCasesMod(pspec)
 118         self.out_z = self.mod.ospec()
 119         self.out_do_z = Signal(reset_less=True)
 120
 121     def setup(self, m, i):
 122         """ links module to inputs and outputs
 123         """
 124         self.mod.setup(m, i, self.out_do_z)
 125         m.d.sync += self.out_z.v.eq(self.mod.out_z.v) # only take the output
 126         m.d.sync += self.out_z.mid.eq(self.mod.o.mid)  # (and mid)
 127
 128     def action(self, m):
 129         self.idsync(m)
 130         with m.If(self.out_do_z):
 131             m.next = "put_z"
 132         with m.Else():
 133             m.next = "denormalise"
 134
 135
 136 class FPDIVSpecialCasesDeNorm(FPState, SimpleHandshake):
 137     """ special cases: NaNs, infs, zeros, denormalised
 138     """
 139
 140     def __init__(self, pspec):
 141         FPState.__init__(self, "special_cases")
 142         self.pspec = pspec
 143         SimpleHandshake.__init__(self, self) # pipe is its own stage
 144         self.out = self.ospec()
 145
 146     def ispec(self):
 147         return FPADDBaseData(self.pspec) # SpecialCases ispec
 148
 149     def ospec(self):
 150         return FPSCData(self.pspec, False) # DeNorm ospec
 151
 152     def setup(self, m, i):
 153         """ links module to inputs and outputs
 154         """
 155         smod = FPDIVSpecialCasesMod(self.pspec)
 156         dmod = FPAddDeNormMod(self.pspec, False)
 157
 158         chain = StageChain([smod, dmod])
 159         chain.setup(m, i)
 160
 161         # only needed for break-out (early-out)
 162         # self.out_do_z = smod.o.out_do_z
 163
 164         self.o = dmod.o
 165
 166     def process(self, i):
 167         return self.o
 168
 169     def action(self, m):
 170         # for break-out (early-out)
 171         #with m.If(self.out_do_z):
 172         #    m.next = "put_z"
 173         #with m.Else():
 174             m.d.sync += self.out.eq(self.process(None))
 175             m.next = "align"
 176
 177