src/ieee754/fpmul/specialcases.py

   1 # IEEE Floating Point Multiplier
   2
   3 from nmigen import Module, Signal, Cat, Const
   4 from nmigen.cli import main, verilog
   5 from math import log
   6
   7 from ieee754.fpcommon.fpbase import FPNumDecode
   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:
  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, width, id_wid):
  22         self.width = width
  23         self.id_wid = id_wid
  24         self.i = self.ispec()
  25         self.o = self.ospec()
  26
  27     def ispec(self):
  28         return FPADDBaseData(self.width, self.id_wid)
  29
  30     def ospec(self):
  31         return FPSCData(self.width, self.id_wid)
  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 = FPNumDecode(None, self.width)
  49         b1 = FPNumDecode(None, self.width)
  50         m.submodules.sc_decode_a = a1
  51         m.submodules.sc_decode_b = 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         s_nomatch = Signal(reset_less=True)
  59         m.d.comb += s_nomatch.eq(a1.s != b1.s)
  60
  61         m_match = Signal(reset_less=True)
  62         m.d.comb += m_match.eq(a1.m == b1.m)
  63
  64         e_match = Signal(reset_less=True)
  65         m.d.comb += e_match.eq(a1.e == b1.e)
  66
  67         aeqmb = Signal(reset_less=True)
  68         m.d.comb += aeqmb.eq(s_nomatch & m_match & e_match)
  69
  70         obz = Signal(reset_less=True)
  71         m.d.comb += obz.eq(a1.is_zero & b1.is_zero)
  72
  73         sabx = Signal(reset_less=True)   # sign a xor b (sabx, get it?)
  74         m.d.comb += sabx.eq(a1.s ^ b1.s)
  75
  76         abnan = Signal(reset_less=True)
  77         m.d.comb += abnan.eq(a1.is_nan | b1.is_nan)
  78
  79         # if a is NaN or b is NaN return NaN
  80         with m.If(abnan):
  81             m.d.comb += self.o.out_do_z.eq(1)
  82             m.d.comb += self.o.z.nan(1)
  83
  84         # if a is inf return inf (or NaN)
  85         with m.Elif(a1.is_inf):
  86             m.d.comb += self.o.out_do_z.eq(1)
  87             m.d.comb += self.o.z.inf(sabx)
  88             # b is zero return NaN
  89             with m.If(b1.is_zero):
  90                 m.d.comb += self.o.z.nan(1)
  91
  92         # if b is inf return inf (or NaN)
  93         with m.Elif(b1.is_inf):
  94             m.d.comb += self.o.out_do_z.eq(1)
  95             m.d.comb += self.o.z.inf(sabx)
  96             # a is zero return NaN
  97             with m.If(a1.is_zero):
  98                 m.d.comb += self.o.z.nan(1)
  99
 100         # if a is zero or b zero return signed-a/b
 101         with m.Elif(obz):
 102             m.d.comb += self.o.out_do_z.eq(1)
 103             m.d.comb += self.o.z.zero(sabx)
 104
 105         # Denormalised Number checks next, so pass a/b data through
 106         with m.Else():
 107             m.d.comb += self.o.out_do_z.eq(0)
 108
 109         m.d.comb += self.o.oz.eq(self.o.z.v)
 110         m.d.comb += self.o.mid.eq(self.i.mid)
 111
 112         return m
 113
 114
 115 class FPMulSpecialCases(FPState):
 116     """ special cases: NaNs, infs, zeros, denormalised
 117         NOTE: some of these are unique to add.  see "Special Operations"
 118         https://steve.hollasch.net/cgindex/coding/ieeefloat.html
 119     """
 120
 121     def __init__(self, width, id_wid):
 122         FPState.__init__(self, "special_cases")
 123         self.mod = FPAddSpecialCasesMod(width)
 124         self.out_z = self.mod.ospec()
 125         self.out_do_z = Signal(reset_less=True)
 126
 127     def setup(self, m, i):
 128         """ links module to inputs and outputs
 129         """
 130         self.mod.setup(m, i, self.out_do_z)
 131         m.d.sync += self.out_z.v.eq(self.mod.out_z.v) # only take the output
 132         m.d.sync += self.out_z.mid.eq(self.mod.o.mid)  # (and mid)
 133
 134     def action(self, m):
 135         self.idsync(m)
 136         with m.If(self.out_do_z):
 137             m.next = "put_z"
 138         with m.Else():
 139             m.next = "denormalise"
 140
 141
 142 class FPMulSpecialCasesDeNorm(FPState, SimpleHandshake):
 143     """ special cases: NaNs, infs, zeros, denormalised
 144     """
 145
 146     def __init__(self, width, id_wid):
 147         FPState.__init__(self, "special_cases")
 148         self.width = width
 149         self.id_wid = id_wid
 150         SimpleHandshake.__init__(self, self) # pipe is its own stage
 151         self.out = self.ospec()
 152
 153     def ispec(self):
 154         return FPADDBaseData(self.width, self.id_wid) # SpecialCases ispec
 155
 156     def ospec(self):
 157         return FPSCData(self.width, self.id_wid) # DeNorm ospec
 158
 159     def setup(self, m, i):
 160         """ links module to inputs and outputs
 161         """
 162         smod = FPMulSpecialCasesMod(self.width, self.id_wid)
 163         dmod = FPAddDeNormMod(self.width, self.id_wid)
 164
 165         chain = StageChain([smod, dmod])
 166         chain.setup(m, i)
 167
 168         # only needed for break-out (early-out)
 169         # self.out_do_z = smod.o.out_do_z
 170
 171         self.o = dmod.o
 172
 173     def process(self, i):
 174         return self.o
 175
 176     def action(self, m):
 177         # for break-out (early-out)
 178         #with m.If(self.out_do_z):
 179         #    m.next = "put_z"
 180         #with m.Else():
 181             m.d.sync += self.out.eq(self.process(None))
 182             m.next = "align"
 183
 184