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             # -ve number is NaN
 108             with m.If(a1.s):
 109                 m.d.comb += self.o.out_do_z.eq(1)
 110                 m.d.comb += self.o.z.nan(0)
 111             # Denormalised Number checks next, so pass a/b data through
 112             with m.Else():
 113                 m.d.comb += self.o.out_do_z.eq(0)
 114
 115
 116         m.d.comb += self.o.oz.eq(self.o.z.v)
 117         m.d.comb += self.o.ctx.eq(self.i.ctx)
 118
 119         return m
 120
 121
 122 class FPDIVSpecialCases(FPState):
 123     """ special cases: NaNs, infs, zeros, denormalised
 124         NOTE: some of these are unique to div.  see "Special Operations"
 125         https://steve.hollasch.net/cgindex/coding/ieeefloat.html
 126     """
 127
 128     def __init__(self, pspec):
 129         FPState.__init__(self, "special_cases")
 130         self.mod = FPDIVSpecialCasesMod(pspec)
 131         self.out_z = self.mod.ospec()
 132         self.out_do_z = Signal(reset_less=True)
 133
 134     def setup(self, m, i):
 135         """ links module to inputs and outputs
 136         """
 137         self.mod.setup(m, i, self.out_do_z)
 138         m.d.sync += self.out_z.v.eq(self.mod.out_z.v) # only take the output
 139         m.d.sync += self.out_z.mid.eq(self.mod.o.mid)  # (and mid)
 140
 141     def action(self, m):
 142         self.idsync(m)
 143         with m.If(self.out_do_z):
 144             m.next = "put_z"
 145         with m.Else():
 146             m.next = "denormalise"
 147
 148
 149 class FPDIVSpecialCasesDeNorm(FPState, SimpleHandshake):
 150     """ special cases: NaNs, infs, zeros, denormalised
 151     """
 152
 153     def __init__(self, pspec):
 154         FPState.__init__(self, "special_cases")
 155         self.pspec = pspec
 156         SimpleHandshake.__init__(self, self) # pipe is its own stage
 157         self.out = self.ospec()
 158
 159     def ispec(self):
 160         return FPADDBaseData(self.pspec) # SpecialCases ispec
 161
 162     def ospec(self):
 163         return FPSCData(self.pspec, False) # Align ospec
 164
 165     def setup(self, m, i):
 166         """ links module to inputs and outputs
 167         """
 168         smod = FPDIVSpecialCasesMod(self.pspec)
 169         dmod = FPAddDeNormMod(self.pspec, False)
 170         amod = FPAlignModSingle(self.pspec, False)
 171
 172         chain = StageChain([smod, dmod, amod])
 173         chain.setup(m, i)
 174
 175         # only needed for break-out (early-out)
 176         # self.out_do_z = smod.o.out_do_z
 177
 178         self.o = amod.o
 179
 180     def process(self, i):
 181         return self.o
 182
 183     def action(self, m):
 184         # for break-out (early-out)
 185         #with m.If(self.out_do_z):
 186         #    m.next = "put_z"
 187         #with m.Else():
 188             m.d.sync += self.out.eq(self.process(None))
 189             m.next = "align"
 190
 191