-# IEEE Floating Point Multiplier
+""" IEEE Floating Point Divider
-from nmigen import Module, Signal, Cat, Const, Elaboratable
+Copyright (C) 2019 Luke Kenneth Casson Leighton <lkcl@lkcl.net>
+Copyright (C) 2019 Jacob Lifshay
+
+Relevant bugreports:
+* http://bugs.libre-riscv.org/show_bug.cgi?id=99
+* http://bugs.libre-riscv.org/show_bug.cgi?id=43
+* http://bugs.libre-riscv.org/show_bug.cgi?id=44
+"""
+
+from nmigen import Module, Signal, Cat, Mux
from nmigen.cli import main, verilog
from math import log
+from nmutil.pipemodbase import PipeModBase, PipeModBaseChain
from ieee754.fpcommon.fpbase import FPNumDecode, FPNumBaseRecord
-from nmutil.singlepipe import SimpleHandshake, StageChain
-
-from ieee754.fpcommon.fpbase import FPState, FPID
-from ieee754.fpcommon.getop import FPADDBaseData
+from ieee754.fpcommon.basedata import FPBaseData
from ieee754.fpcommon.denorm import (FPSCData, FPAddDeNormMod)
+from ieee754.fpmul.align import FPAlignModSingle
+from ieee754.div_rem_sqrt_rsqrt.core import DivPipeCoreOperation as DP
-class FPDIVSpecialCasesMod(Elaboratable):
+class FPDIVSpecialCasesMod(PipeModBase):
""" special cases: NaNs, infs, zeros, denormalised
see "Special Operations"
https://steve.hollasch.net/cgindex/coding/ieeefloat.html
"""
- def __init__(self, width, id_wid):
- self.width = width
- self.id_wid = id_wid
- self.i = self.ispec()
- self.o = self.ospec()
+ def __init__(self, pspec):
+ super().__init__(pspec, "specialcases")
def ispec(self):
- return FPADDBaseData(self.width, self.id_wid)
+ return FPBaseData(self.pspec)
def ospec(self):
- return FPSCData(self.width, self.id_wid, False)
-
- def setup(self, m, i):
- """ links module to inputs and outputs
- """
- m.submodules.specialcases = self
- m.d.comb += self.i.eq(i)
-
- def process(self, i):
- return self.o
+ return FPSCData(self.pspec, False)
def elaborate(self, platform):
m = Module()
-
- #m.submodules.sc_out_z = self.o.z
+ comb = m.d.comb
# decode: XXX really should move to separate stage
- a1 = FPNumBaseRecord(self.width, False)
- b1 = FPNumBaseRecord(self.width, False)
+ width = self.pspec.width
+ a1 = FPNumBaseRecord(width, False, name="a1")
+ b1 = FPNumBaseRecord(width, False, name="b1")
m.submodules.sc_decode_a = a1 = FPNumDecode(None, a1)
m.submodules.sc_decode_b = b1 = FPNumDecode(None, b1)
- m.d.comb += [a1.v.eq(self.i.a),
+ comb += [a1.v.eq(self.i.a),
b1.v.eq(self.i.b),
self.o.a.eq(a1),
self.o.b.eq(b1)
- ]
+ ]
+ # temporaries (used below)
sabx = Signal(reset_less=True) # sign a xor b (sabx, get it?)
- m.d.comb += sabx.eq(a1.s ^ b1.s)
-
- abnan = Signal(reset_less=True)
- m.d.comb += abnan.eq(a1.is_nan | b1.is_nan)
-
- abinf = Signal(reset_less=True)
- m.d.comb += abinf.eq(a1.is_inf & b1.is_inf)
-
- # if a is NaN or b is NaN return NaN
- with m.If(abnan):
- m.d.comb += self.o.out_do_z.eq(1)
- m.d.comb += self.o.z.nan(1)
-
- # if a is inf and b is Inf return NaN
- with m.Elif(abnan):
- m.d.comb += self.o.out_do_z.eq(1)
- m.d.comb += self.o.z.nan(1)
-
- # if a is inf return inf
- with m.Elif(a1.is_inf):
- m.d.comb += self.o.out_do_z.eq(1)
- m.d.comb += self.o.z.inf(sabx)
-
- # if b is inf return zero
- with m.Elif(b1.is_inf):
- m.d.comb += self.o.out_do_z.eq(1)
- m.d.comb += self.o.z.zero(sabx)
-
- # if a is zero return zero (or NaN if b is zero)
- with m.Elif(a1.is_zero):
- m.d.comb += self.o.out_do_z.eq(1)
- m.d.comb += self.o.z.zero(sabx)
- # b is zero return NaN
- with m.If(b1.is_zero):
- m.d.comb += self.o.z.nan(1)
-
- # if b is zero return Inf
- with m.Elif(b1.is_zero):
- m.d.comb += self.o.out_do_z.eq(1)
- m.d.comb += self.o.z.inf(sabx)
-
- # Denormalised Number checks next, so pass a/b data through
- with m.Else():
- m.d.comb += self.o.out_do_z.eq(0)
-
- m.d.comb += self.o.oz.eq(self.o.z.v)
- m.d.comb += self.o.mid.eq(self.i.mid)
+ t_abnan = Signal(reset_less=True)
+ t_abinf = Signal(reset_less=True)
+ t_a1inf = Signal(reset_less=True)
+ t_b1inf = Signal(reset_less=True)
+ t_a1nan = Signal(reset_less=True)
+ t_a1zero = Signal(reset_less=True)
+ t_b1zero = Signal(reset_less=True)
+ t_abz = Signal(reset_less=True)
+ t_special_div = Signal(reset_less=True)
+ t_special_sqrt = Signal(reset_less=True)
+ t_special_rsqrt = Signal(reset_less=True)
+
+ comb += sabx.eq(a1.s ^ b1.s)
+ comb += t_abnan.eq(a1.is_nan | b1.is_nan)
+ comb += t_abinf.eq(a1.is_inf & b1.is_inf)
+ comb += t_a1inf.eq(a1.is_inf)
+ comb += t_b1inf.eq(b1.is_inf)
+ comb += t_a1nan.eq(a1.is_nan)
+ comb += t_abz.eq(a1.is_zero & b1.is_zero)
+ comb += t_a1zero.eq(a1.is_zero)
+ comb += t_b1zero.eq(b1.is_zero)
+
+ # prepare inf/zero/nans
+ z_zero = FPNumBaseRecord(width, False, name="z_zero")
+ z_zeroa = FPNumBaseRecord(width, False, name="z_zeroa")
+ z_zeroab = FPNumBaseRecord(width, False, name="z_zeroab")
+ z_nan = FPNumBaseRecord(width, False, name="z_nan")
+ z_infa = FPNumBaseRecord(width, False, name="z_infa")
+ z_infb = FPNumBaseRecord(width, False, name="z_infb")
+ z_infab = FPNumBaseRecord(width, False, name="z_infab")
+ comb += z_zero.zero(0)
+ comb += z_zeroa.zero(a1.s)
+ comb += z_zeroab.zero(sabx)
+ comb += z_nan.nan(0)
+ comb += z_infa.inf(a1.s)
+ comb += z_infb.inf(b1.s)
+ comb += z_infab.inf(sabx)
+
+ comb += t_special_div.eq(Cat(t_b1zero, t_a1zero, t_b1inf, t_a1inf,
+ t_abinf, t_abnan).bool())
+ comb += t_special_sqrt.eq(Cat(t_a1zero, a1.s, t_a1inf,
+ t_a1nan).bool())
+
+ # select one of 3 different sets of specialcases (DIV, SQRT, RSQRT)
+ with m.Switch(self.i.ctx.op):
+
+ ########## DIV ############
+ with m.Case(int(DP.UDivRem)):
+
+ # any special cases?
+ comb += self.o.out_do_z.eq(t_special_div)
+
+ # if a is NaN or b is NaN return NaN
+ # if a is inf and b is Inf return NaN
+ # if a is inf return inf
+ # if b is inf return zero
+ # if a is zero return zero (or NaN if b is zero)
+ # b is zero return NaN
+ # if b is zero return Inf
+
+ # sigh inverse order on the above, Mux-cascade
+ oz = 0
+ oz = Mux(t_b1zero, z_infab.v, oz)
+ oz = Mux(t_a1zero, Mux(t_b1zero, z_nan.v, z_zeroab.v), oz)
+ oz = Mux(t_b1inf, z_zeroab.v, oz)
+ oz = Mux(t_a1inf, z_infab.v, oz)
+ oz = Mux(t_abinf, z_nan.v, oz)
+ oz = Mux(t_abnan, z_nan.v, oz)
+
+ comb += self.o.oz.eq(oz)
+
+ ########## SQRT ############
+ with m.Case(int(DP.SqrtRem)):
+
+ # any special cases?
+ comb += self.o.out_do_z.eq(t_special_sqrt)
+
+ # if a is zero return zero
+ # -ve number is NaN
+ # if a is inf return inf
+ # if a is NaN return NaN
+
+ oz = 0
+ oz = Mux(t_a1nan, z_nan.v, oz)
+ oz = Mux(t_a1inf, z_infab.v, oz)
+ oz = Mux(a1.s, z_nan.v, oz)
+ oz = Mux(t_a1zero, z_zeroa.v, oz)
+
+ comb += self.o.oz.eq(oz)
+
+ ########## RSQRT ############
+ with m.Case(int(DP.RSqrtRem)):
+
+ # if a is NaN return canonical NaN
+ with m.If(a1.is_nan):
+ comb += self.o.z.nan(0)
+
+ # if a is +/- zero return +/- INF
+ with m.Elif(a1.is_zero):
+ # this includes the "weird" case 1/sqrt(-0) == -Inf
+ comb += self.o.z.inf(a1.s)
+
+ # -ve number is canonical NaN
+ with m.Elif(a1.s):
+ comb += self.o.z.nan(0)
+
+ # if a is inf return zero (-ve already excluded, above)
+ with m.Elif(a1.is_inf):
+ comb += self.o.z.zero(0)
+
+ # Denormalised Number checks next, so pass a/b data through
+ with m.Else():
+ comb += self.o.out_do_z.eq(0)
+
+ comb += self.o.oz.eq(self.o.z.v)
+
+ # pass through context
+ comb += self.o.ctx.eq(self.i.ctx)
return m
-class FPDIVSpecialCases(FPState):
+class FPDIVSpecialCasesDeNorm(PipeModBaseChain):
""" special cases: NaNs, infs, zeros, denormalised
- NOTE: some of these are unique to div. see "Special Operations"
- https://steve.hollasch.net/cgindex/coding/ieeefloat.html
"""
- def __init__(self, width, id_wid):
- FPState.__init__(self, "special_cases")
- self.mod = FPDIVSpecialCasesMod(width)
- self.out_z = self.mod.ospec()
- self.out_do_z = Signal(reset_less=True)
-
- def setup(self, m, i):
+ def get_chain(self):
""" links module to inputs and outputs
"""
- self.mod.setup(m, i, self.out_do_z)
- m.d.sync += self.out_z.v.eq(self.mod.out_z.v) # only take the output
- m.d.sync += self.out_z.mid.eq(self.mod.o.mid) # (and mid)
-
- def action(self, m):
- self.idsync(m)
- with m.If(self.out_do_z):
- m.next = "put_z"
- with m.Else():
- m.next = "denormalise"
-
-
-class FPDIVSpecialCasesDeNorm(FPState, SimpleHandshake):
- """ special cases: NaNs, infs, zeros, denormalised
- """
-
- def __init__(self, width, id_wid):
- FPState.__init__(self, "special_cases")
- self.width = width
- self.id_wid = id_wid
- SimpleHandshake.__init__(self, self) # pipe is its own stage
- self.out = self.ospec()
-
- def ispec(self):
- return FPADDBaseData(self.width, self.id_wid) # SpecialCases ispec
-
- def ospec(self):
- return FPSCData(self.width, self.id_wid, False) # DeNorm ospec
-
- def setup(self, m, i):
- """ links module to inputs and outputs
- """
- smod = FPDIVSpecialCasesMod(self.width, self.id_wid)
- dmod = FPAddDeNormMod(self.width, self.id_wid, False)
-
- chain = StageChain([smod, dmod])
- chain.setup(m, i)
-
- # only needed for break-out (early-out)
- # self.out_do_z = smod.o.out_do_z
-
- self.o = dmod.o
-
- def process(self, i):
- return self.o
-
- def action(self, m):
- # for break-out (early-out)
- #with m.If(self.out_do_z):
- # m.next = "put_z"
- #with m.Else():
- m.d.sync += self.out.eq(self.process(None))
- m.next = "align"
-
+ smod = FPDIVSpecialCasesMod(self.pspec)
+ dmod = FPAddDeNormMod(self.pspec, False)
+ amod = FPAlignModSingle(self.pspec, False)
+ return [smod, dmod, amod]
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