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 StageChain
   9
  10 from ieee754.pipeline import DynamicPipe
  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 FPMulSpecialCasesMod(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         width = self.pspec.width
  49         a1 = FPNumBaseRecord(width, False)
  50         b1 = FPNumBaseRecord(width, False)
  51         m.submodules.sc_decode_a = a1 = FPNumDecode(None, a1)
  52         m.submodules.sc_decode_b = b1 = FPNumDecode(None, b1)
  53         m.d.comb += [a1.v.eq(self.i.a),
  54                      b1.v.eq(self.i.b),
  55                      self.o.a.eq(a1),
  56                      self.o.b.eq(b1)
  57                     ]
  58
  59         obz = Signal(reset_less=True)
  60         m.d.comb += obz.eq(a1.is_zero | b1.is_zero)
  61
  62         sabx = Signal(reset_less=True)   # sign a xor b (sabx, get it?)
  63         m.d.comb += sabx.eq(a1.s ^ b1.s)
  64
  65         abnan = Signal(reset_less=True)
  66         m.d.comb += abnan.eq(a1.is_nan | b1.is_nan)
  67
  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 return inf (or NaN)
  74         with m.Elif(a1.is_inf):
  75             m.d.comb += self.o.out_do_z.eq(1)
  76             m.d.comb += self.o.z.inf(sabx)
  77             # b is zero return NaN
  78             with m.If(b1.is_zero):
  79                 m.d.comb += self.o.z.nan(0)
  80
  81         # if b is inf return inf (or NaN)
  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.inf(sabx)
  85             # a is zero return NaN
  86             with m.If(a1.is_zero):
  87                 m.d.comb += self.o.z.nan(0)
  88
  89         # if a is zero or b zero return signed-a/b
  90         with m.Elif(obz):
  91             m.d.comb += self.o.out_do_z.eq(1)
  92             m.d.comb += self.o.z.zero(sabx)
  93
  94         # Denormalised Number checks next, so pass a/b data through
  95         with m.Else():
  96             m.d.comb += self.o.out_do_z.eq(0)
  97
  98         m.d.comb += self.o.oz.eq(self.o.z.v)
  99         m.d.comb += self.o.ctx.eq(self.i.ctx)
 100
 101         return m
 102
 103
 104 class FPMulSpecialCasesDeNorm(DynamicPipe):
 105     """ special cases: NaNs, infs, zeros, denormalised
 106     """
 107
 108     def __init__(self, pspec):
 109         self.pspec = pspec
 110         super().__init__(pspec)
 111         self.out = self.ospec()
 112
 113     def ispec(self):
 114         return FPADDBaseData(self.pspec)
 115
 116     def ospec(self):
 117         return FPSCData(self.pspec, False)
 118
 119     def setup(self, m, i):
 120         """ links module to inputs and outputs
 121         """
 122         smod = FPMulSpecialCasesMod(self.pspec)
 123         dmod = FPAddDeNormMod(self.pspec, False)
 124         amod = FPAlignModSingle(self.pspec, False)
 125
 126         chain = StageChain([smod, dmod, amod])
 127         chain.setup(m, i)
 128
 129         # only needed for break-out (early-out)
 130         # self.out_do_z = smod.o.out_do_z
 131
 132         self.o = amod.o # output is from last .o in the chain
 133
 134     def process(self, i):
 135         return self.o
 136