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, FPNumBaseRecord
   8
   9 from nmutil.pipemodbase import PipeModBase, PipeModBaseChain
  10 from ieee754.fpcommon.basedata import FPBaseData
  11 from ieee754.fpcommon.denorm import (FPSCData, FPAddDeNormMod)
  12 from ieee754.fpmul.align import FPAlignModSingle
  13
  14
  15 class FPMulSpecialCasesMod(PipeModBase):
  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         super().__init__(pspec, "specialcases")
  23
  24     def ispec(self):
  25         return FPBaseData(self.pspec)
  26
  27     def ospec(self):
  28         return FPSCData(self.pspec, False)
  29
  30     def elaborate(self, platform):
  31         m = Module()
  32         comb = m.d.comb
  33
  34         # decode: XXX really should move to separate stage
  35         width = self.pspec.width
  36         a1 = FPNumBaseRecord(width, False)
  37         b1 = FPNumBaseRecord(width, False)
  38         m.submodules.sc_decode_a = a1 = FPNumDecode(None, a1)
  39         m.submodules.sc_decode_b = b1 = FPNumDecode(None, b1)
  40         comb += [a1.v.eq(self.i.a),
  41                      b1.v.eq(self.i.b),
  42                      self.o.a.eq(a1),
  43                      self.o.b.eq(b1)
  44                     ]
  45
  46         obz = Signal(reset_less=True)
  47         comb += obz.eq(a1.is_zero | b1.is_zero)
  48
  49         sabx = Signal(reset_less=True)   # sign a xor b (sabx, get it?)
  50         comb += sabx.eq(a1.s ^ b1.s)
  51
  52         abnan = Signal(reset_less=True)
  53         comb += abnan.eq(a1.is_nan | b1.is_nan)
  54
  55         # initialise and override if needed
  56         comb += self.o.out_do_z.eq(1)
  57
  58         # if a is NaN or b is NaN return NaN
  59         with m.If(abnan):
  60             comb += self.o.z.nan(0)
  61
  62         # if a is inf return inf (or NaN)
  63         with m.Elif(a1.is_inf):
  64             comb += self.o.z.inf(sabx)
  65             # b is zero return NaN
  66             with m.If(b1.is_zero):
  67                 comb += self.o.z.nan(0)
  68
  69         # if b is inf return inf (or NaN)
  70         with m.Elif(b1.is_inf):
  71             comb += self.o.z.inf(sabx)
  72             # a is zero return NaN
  73             with m.If(a1.is_zero):
  74                 comb += self.o.z.nan(0)
  75
  76         # if a is zero or b zero return signed-a/b
  77         with m.Elif(obz):
  78             comb += self.o.z.zero(sabx)
  79
  80         # Denormalised Number checks next, so pass a/b data through
  81         with m.Else():
  82             comb += self.o.out_do_z.eq(0)
  83
  84         comb += self.o.oz.eq(self.o.z.v)
  85         comb += self.o.ctx.eq(self.i.ctx)
  86
  87         return m
  88
  89
  90 class FPMulSpecialCasesDeNorm(PipeModBaseChain):
  91     """ special cases: NaNs, infs, zeros, denormalised
  92     """
  93
  94     def get_chain(self):
  95         """ gets chain of modules
  96         """
  97         smod = FPMulSpecialCasesMod(self.pspec)
  98         dmod = FPAddDeNormMod(self.pspec, False)
  99         amod = FPAlignModSingle(self.pspec, False)
 100
 101         return [smod, dmod, amod]
 102