src/ieee754/fpcommon/denorm.py

   1 # IEEE Floating Point Adder (Single Precision)
   2 # Copyright (C) Jonathan P Dawson 2013
   3 # 2013-12-12
   4
   5 from nmigen import Module, Signal
   6 from nmigen.cli import main, verilog
   7 from math import log
   8
   9 from ieee754.fpcommon.modbase import FPModBase
  10 from ieee754.fpcommon.fpbase import FPNumBaseRecord
  11 from ieee754.fpcommon.fpbase import FPNumBase
  12 from ieee754.fpcommon.getop import FPPipeContext
  13
  14
  15 class FPSCData:
  16
  17     def __init__(self, pspec, m_extra):
  18         width = pspec.width
  19         # NOTE: difference between z and oz is that oz is created by
  20         # special-cases module(s) and will propagate, along with its
  21         # "bypass" signal out_do_z, through the pipeline, *disabling*
  22         # all processing of all subsequent stages.
  23         self.a = FPNumBaseRecord(width, m_extra, name="a")   # operand a
  24         self.b = FPNumBaseRecord(width, m_extra, name="b")   # operand b
  25         self.z = FPNumBaseRecord(width, False, name="z")     # denormed result
  26         self.oz = Signal(width, reset_less=True)   # "finished" (bypass) result
  27         self.out_do_z = Signal(reset_less=True)    # "bypass" enabled
  28         self.ctx = FPPipeContext(pspec)
  29         self.muxid = self.ctx.muxid
  30
  31     def __iter__(self):
  32         yield from self.a
  33         yield from self.b
  34         yield from self.z
  35         yield self.oz
  36         yield self.out_do_z
  37         yield from self.ctx
  38
  39     def eq(self, i):
  40         ret = [self.z.eq(i.z), self.out_do_z.eq(i.out_do_z), self.oz.eq(i.oz),
  41                self.a.eq(i.a), self.b.eq(i.b), self.ctx.eq(i.ctx)]
  42         return ret
  43
  44
  45 class FPAddDeNormMod(FPModBase):
  46
  47     def __init__(self, pspec, m_extra):
  48         self.m_extra = m_extra
  49         super().__init__(pspec, "denormalise")
  50
  51     def ispec(self):
  52         return FPSCData(self.pspec, self.m_extra)
  53
  54     def ospec(self):
  55         return FPSCData(self.pspec, self.m_extra)
  56
  57     def elaborate(self, platform):
  58         m = Module()
  59         comb = m.d.comb
  60
  61         m.submodules.denorm_in_a = in_a = FPNumBase(self.i.a)
  62         m.submodules.denorm_in_b = in_b = FPNumBase(self.i.b)
  63
  64         with m.If(~self.i.out_do_z):
  65             # XXX hmmm, don't like repeating identical code
  66             comb += self.o.a.eq(self.i.a)
  67             with m.If(in_a.exp_n127):
  68                 comb += self.o.a.e.eq(self.i.a.N126)  # limit a exponent
  69             with m.Else():
  70                 comb += self.o.a.m[-1].eq(1)  # set top mantissa bit
  71
  72             comb += self.o.b.eq(self.i.b)
  73             with m.If(in_b.exp_n127):
  74                 comb += self.o.b.e.eq(self.i.b.N126)  # limit a exponent
  75             with m.Else():
  76                 comb += self.o.b.m[-1].eq(1)  # set top mantissa bit
  77
  78         comb += self.o.ctx.eq(self.i.ctx)
  79         comb += self.o.z.eq(self.i.z)
  80         comb += self.o.out_do_z.eq(self.i.out_do_z)
  81         comb += self.o.oz.eq(self.i.oz)
  82
  83         return m
  84
  85