src/ieee754/fpcommon/roundz.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, Mux
   6
   7 from nmutil.pipemodbase import PipeModBase
   8 from ieee754.fpcommon.fpbase import FPNumBaseRecord, FPRoundingMode
   9 from ieee754.fpcommon.getop import FPPipeContext
  10 from ieee754.fpcommon.postnormalise import FPNorm1Data
  11
  12
  13 class FPRoundData:
  14
  15     def __init__(self, pspec):
  16         width = pspec.width
  17         self.z = FPNumBaseRecord(width, False, name="z")
  18         self.ctx = FPPipeContext(pspec)
  19         self.muxid = self.ctx.muxid
  20         # pipeline bypass [data comes from specialcases]
  21         self.out_do_z = Signal(reset_less=True)
  22         self.oz = Signal(width, reset_less=True)
  23
  24         self.rm = Signal(FPRoundingMode, reset=FPRoundingMode.DEFAULT)
  25         """rounding mode"""
  26
  27     def eq(self, i):
  28         ret = [self.z.eq(i.z), self.out_do_z.eq(i.out_do_z), self.oz.eq(i.oz),
  29                self.ctx.eq(i.ctx), self.rm.eq(i.rm)]
  30         return ret
  31
  32
  33 class FPRoundMod(PipeModBase):
  34
  35     def __init__(self, pspec):
  36         super().__init__(pspec, "roundz")
  37
  38     def ispec(self):
  39         return FPNorm1Data(self.pspec)
  40
  41     def ospec(self):
  42         return FPRoundData(self.pspec)
  43
  44     def elaborate(self, platform):
  45         m = Module()
  46         comb = m.d.comb
  47
  48         comb += self.o.eq(self.i)  # copies muxid, z, out_do_z
  49         im = self.i.z.m
  50         ie = self.i.z.e
  51         msb1s = Signal(reset_less=True)
  52         comb += msb1s.eq(self.i.z.m.all())  # all 1s
  53         comb += self.o.z.m.eq(Mux(self.i.roundz, im+1, im))  # mantissa up
  54         comb += self.o.z.e.eq(Mux(msb1s & self.i.roundz, ie + 1, ie)) # exp up
  55
  56         return m