src/ieee754/fpmul/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 FPMulSpecialCasesMod(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         width = self.pspec['width']
  48         a1 = FPNumBaseRecord(width, False)
  49         b1 = FPNumBaseRecord(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         obz = Signal(reset_less=True)
  59         m.d.comb += obz.eq(a1.is_zero | b1.is_zero)
  60
  61         sabx = Signal(reset_less=True)   # sign a xor b (sabx, get it?)
  62         m.d.comb += sabx.eq(a1.s ^ b1.s)
  63
  64         abnan = Signal(reset_less=True)
  65         m.d.comb += abnan.eq(a1.is_nan | b1.is_nan)
  66
  67         # if a is NaN or b is NaN return NaN
  68         with m.If(abnan):
  69             m.d.comb += self.o.out_do_z.eq(1)
  70             m.d.comb += self.o.z.nan(0)
  71
  72         # if a is inf return inf (or NaN)
  73         with m.Elif(a1.is_inf):
  74             m.d.comb += self.o.out_do_z.eq(1)
  75             m.d.comb += self.o.z.inf(sabx)
  76             # b is zero return NaN
  77             with m.If(b1.is_zero):
  78                 m.d.comb += self.o.z.nan(0)
  79
  80         # if b is inf return inf (or NaN)
  81         with m.Elif(b1.is_inf):
  82             m.d.comb += self.o.out_do_z.eq(1)
  83             m.d.comb += self.o.z.inf(sabx)
  84             # a is zero return NaN
  85             with m.If(a1.is_zero):
  86                 m.d.comb += self.o.z.nan(0)
  87
  88         # if a is zero or b zero return signed-a/b
  89         with m.Elif(obz):
  90             m.d.comb += self.o.out_do_z.eq(1)
  91             m.d.comb += self.o.z.zero(sabx)
  92
  93         # Denormalised Number checks next, so pass a/b data through
  94         with m.Else():
  95             m.d.comb += self.o.out_do_z.eq(0)
  96
  97         m.d.comb += self.o.oz.eq(self.o.z.v)
  98         m.d.comb += self.o.ctx.eq(self.i.ctx)
  99
 100         return m
 101
 102
 103 class FPMulSpecialCases(FPState):
 104     """ special cases: NaNs, infs, zeros, denormalised
 105         NOTE: some of these are unique to add.  see "Special Operations"
 106         https://steve.hollasch.net/cgindex/coding/ieeefloat.html
 107     """
 108
 109     def __init__(self, width, id_wid):
 110         FPState.__init__(self, "special_cases")
 111         self.mod = FPMulSpecialCasesMod(width)
 112         self.out_z = self.mod.ospec()
 113         self.out_do_z = Signal(reset_less=True)
 114
 115     def setup(self, m, i):
 116         """ links module to inputs and outputs
 117         """
 118         self.mod.setup(m, i, self.out_do_z)
 119         m.d.sync += self.out_z.v.eq(self.mod.out_z.v) # only take the output
 120         m.d.sync += self.out_z.ctx.eq(self.mod.o.ctx)  # (and context)
 121
 122     def action(self, m):
 123         self.idsync(m)
 124         with m.If(self.out_do_z):
 125             m.next = "put_z"
 126         with m.Else():
 127             m.next = "denormalise"
 128
 129
 130 class FPMulSpecialCasesDeNorm(FPState, SimpleHandshake):
 131     """ special cases: NaNs, infs, zeros, denormalised
 132     """
 133
 134     def __init__(self, pspec):
 135         FPState.__init__(self, "special_cases")
 136         self.pspec = pspec
 137         SimpleHandshake.__init__(self, self) # pipe is its own stage
 138         self.out = self.ospec()
 139
 140     def ispec(self):
 141         return FPADDBaseData(self.pspec)
 142
 143     def ospec(self):
 144         return FPSCData(self.pspec, False)
 145
 146     def setup(self, m, i):
 147         """ links module to inputs and outputs
 148         """
 149         smod = FPMulSpecialCasesMod(self.pspec)
 150         dmod = FPAddDeNormMod(self.pspec, False)
 151
 152         chain = StageChain([smod, dmod])
 153         chain.setup(m, i)
 154
 155         # only needed for break-out (early-out)
 156         # self.out_do_z = smod.o.out_do_z
 157
 158         self.o = dmod.o
 159
 160     def process(self, i):
 161         return self.o
 162
 163     def action(self, m):
 164         # for break-out (early-out)
 165         #with m.If(self.out_do_z):
 166         #    m.next = "put_z"
 167         #with m.Else():
 168             m.d.sync += self.out.eq(self.process(None))
 169             m.next = "align"
 170
 171