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 from ieee754.fpmul.align import FPAlignModSingle
  14
  15
  16 class FPDIVSpecialCasesMod(Elaboratable):
  17     """ special cases: NaNs, infs, zeros, denormalised
  18         see "Special Operations"
  19         https://steve.hollasch.net/cgindex/coding/ieeefloat.html
  20     """
  21
  22     def __init__(self, pspec):
  23         self.pspec = pspec
  24         self.i = self.ispec()
  25         self.o = self.ospec()
  26
  27     def ispec(self):
  28         return FPADDBaseData(self.pspec)
  29
  30     def ospec(self):
  31         return FPSCData(self.pspec, False)
  32
  33     def setup(self, m, i):
  34         """ links module to inputs and outputs
  35         """
  36         m.submodules.specialcases = self
  37         m.d.comb += self.i.eq(i)
  38
  39     def process(self, i):
  40         return self.o
  41
  42     def elaborate(self, platform):
  43         m = Module()
  44
  45         #m.submodules.sc_out_z = self.o.z
  46
  47         # decode: XXX really should move to separate stage
  48         a1 = FPNumBaseRecord(self.pspec.width, False)
  49         b1 = FPNumBaseRecord(self.pspec.width, False)
  50         m.submodules.sc_decode_a = a1 = FPNumDecode(None, a1)
  51         m.submodules.sc_decode_b = b1 = FPNumDecode(None, b1)
  52         m.d.comb += [a1.v.eq(self.i.a),
  53                      b1.v.eq(self.i.b),
  54                      self.o.a.eq(a1),
  55                      self.o.b.eq(b1)
  56                     ]
  57
  58         sabx = Signal(reset_less=True)   # sign a xor b (sabx, get it?)
  59         m.d.comb += sabx.eq(a1.s ^ b1.s)
  60
  61         abnan = Signal(reset_less=True)
  62         m.d.comb += abnan.eq(a1.is_nan | b1.is_nan)
  63
  64         abinf = Signal(reset_less=True)
  65         m.d.comb += abinf.eq(a1.is_inf & b1.is_inf)
  66
  67         with m.If(self.i.ctx.op == 0): # DIV
  68             # if a is NaN or b is NaN return NaN
  69             with m.If(abnan):
  70                 m.d.comb += self.o.out_do_z.eq(1)
  71                 m.d.comb += self.o.z.nan(0)
  72
  73             # if a is inf and b is Inf return NaN
  74             with m.Elif(abinf):
  75                 m.d.comb += self.o.out_do_z.eq(1)
  76                 m.d.comb += self.o.z.nan(0)
  77
  78             # if a is inf return inf
  79             with m.Elif(a1.is_inf):
  80                 m.d.comb += self.o.out_do_z.eq(1)
  81                 m.d.comb += self.o.z.inf(sabx)
  82
  83             # if b is inf return zero
  84             with m.Elif(b1.is_inf):
  85                 m.d.comb += self.o.out_do_z.eq(1)
  86                 m.d.comb += self.o.z.zero(sabx)
  87
  88             # if a is zero return zero (or NaN if b is zero)
  89             with m.Elif(a1.is_zero):
  90                 m.d.comb += self.o.out_do_z.eq(1)
  91                 m.d.comb += self.o.z.zero(sabx)
  92                 # b is zero return NaN
  93                 with m.If(b1.is_zero):
  94                     m.d.comb += self.o.z.nan(0)
  95
  96             # if b is zero return Inf
  97             with m.Elif(b1.is_zero):
  98                 m.d.comb += self.o.out_do_z.eq(1)
  99                 m.d.comb += self.o.z.inf(sabx)
 100
 101             # Denormalised Number checks next, so pass a/b data through
 102             with m.Else():
 103                 m.d.comb += self.o.out_do_z.eq(0)
 104
 105         with m.If(self.i.ctx.op == 1): # SQRT
 106
 107             # if a is zero return zero
 108             with m.If(a1.is_zero):
 109                 m.d.comb += self.o.out_do_z.eq(1)
 110                 m.d.comb += self.o.z.zero(a1.s)
 111
 112             # -ve number is NaN
 113             with m.Elif(a1.s):
 114                 m.d.comb += self.o.out_do_z.eq(1)
 115                 m.d.comb += self.o.z.nan(0)
 116
 117             # if a is inf return inf
 118             with m.Elif(a1.is_inf):
 119                 m.d.comb += self.o.out_do_z.eq(1)
 120                 m.d.comb += self.o.z.inf(sabx)
 121
 122             # if a is NaN return NaN
 123             with m.Elif(a1.is_nan):
 124                 m.d.comb += self.o.out_do_z.eq(1)
 125                 m.d.comb += self.o.z.nan(0)
 126
 127             # Denormalised Number checks next, so pass a/b data through
 128             with m.Else():
 129                 m.d.comb += self.o.out_do_z.eq(0)
 130
 131         with m.If(self.i.ctx.op == 2): # RSQRT
 132
 133             # if a is NaN return canonical NaN
 134             with m.If(a1.is_nan):
 135                 m.d.comb += self.o.out_do_z.eq(1)
 136                 m.d.comb += self.o.z.nan(0)
 137
 138             # if a is +/- zero return +/- INF
 139             with m.Elif(a1.is_zero):
 140                 m.d.comb += self.o.out_do_z.eq(1)
 141                 # this includes the "weird" case 1/sqrt(-0) == -Inf
 142                 m.d.comb += self.o.z.inf(a1.s)
 143
 144             # -ve number is canonical NaN
 145             with m.Elif(a1.s):
 146                 m.d.comb += self.o.out_do_z.eq(1)
 147                 m.d.comb += self.o.z.nan(0)
 148
 149             # if a is inf return zero (-ve already excluded, above)
 150             with m.Elif(a1.is_inf):
 151                 m.d.comb += self.o.out_do_z.eq(1)
 152                 m.d.comb += self.o.z.zero(0)
 153
 154             # Denormalised Number checks next, so pass a/b data through
 155             with m.Else():
 156                 m.d.comb += self.o.out_do_z.eq(0)
 157
 158
 159         m.d.comb += self.o.oz.eq(self.o.z.v)
 160         m.d.comb += self.o.ctx.eq(self.i.ctx)
 161
 162         return m
 163
 164
 165 class FPDIVSpecialCases(FPState):
 166     """ special cases: NaNs, infs, zeros, denormalised
 167         NOTE: some of these are unique to div.  see "Special Operations"
 168         https://steve.hollasch.net/cgindex/coding/ieeefloat.html
 169     """
 170
 171     def __init__(self, pspec):
 172         FPState.__init__(self, "special_cases")
 173         self.mod = FPDIVSpecialCasesMod(pspec)
 174         self.out_z = self.mod.ospec()
 175         self.out_do_z = Signal(reset_less=True)
 176
 177     def setup(self, m, i):
 178         """ links module to inputs and outputs
 179         """
 180         self.mod.setup(m, i, self.out_do_z)
 181         m.d.sync += self.out_z.v.eq(self.mod.out_z.v) # only take the output
 182         m.d.sync += self.out_z.mid.eq(self.mod.o.mid)  # (and mid)
 183
 184     def action(self, m):
 185         self.idsync(m)
 186         with m.If(self.out_do_z):
 187             m.next = "put_z"
 188         with m.Else():
 189             m.next = "denormalise"
 190
 191
 192 class FPDIVSpecialCasesDeNorm(FPState, SimpleHandshake):
 193     """ special cases: NaNs, infs, zeros, denormalised
 194     """
 195
 196     def __init__(self, pspec):
 197         FPState.__init__(self, "special_cases")
 198         self.pspec = pspec
 199         SimpleHandshake.__init__(self, self) # pipe is its own stage
 200         self.out = self.ospec()
 201
 202     def ispec(self):
 203         return FPADDBaseData(self.pspec) # SpecialCases ispec
 204
 205     def ospec(self):
 206         return FPSCData(self.pspec, False) # Align ospec
 207
 208     def setup(self, m, i):
 209         """ links module to inputs and outputs
 210         """
 211         smod = FPDIVSpecialCasesMod(self.pspec)
 212         dmod = FPAddDeNormMod(self.pspec, False)
 213         amod = FPAlignModSingle(self.pspec, False)
 214
 215         chain = StageChain([smod, dmod, amod])
 216         chain.setup(m, i)
 217
 218         # only needed for break-out (early-out)
 219         # self.out_do_z = smod.o.out_do_z
 220
 221         self.o = amod.o
 222
 223     def process(self, i):
 224         return self.o
 225
 226     def action(self, m):
 227         # for break-out (early-out)
 228         #with m.If(self.out_do_z):
 229         #    m.next = "put_z"
 230         #with m.Else():
 231             m.d.sync += self.out.eq(self.process(None))
 232             m.next = "align"
 233
 234