from nmigen import Module, Signal, Const
from nmigen.cli import main, verilog
-from ieee754.fpcommon.modbase import FPModBase
-from ieee754.fpcommon.getop import FPADDBaseData
-from ieee754.fpcommon.postcalc import FPAddStage1Data
-from ieee754.fpcommon.msbhigh import FPMSBHigh
-from ieee754.fpcommon.exphigh import FPEXPHigh
+from nmutil.pipemodbase import PipeModBase
+from ieee754.fpcommon.basedata import FPBaseData
+from ieee754.fpcommon.postcalc import FPPostCalcData
from ieee754.fpcommon.fpbase import FPNumDecode, FPNumBaseRecord
-class FPCVTDownConvertMod(FPModBase):
+class FPCVTDownConvertMod(PipeModBase):
""" FP down-conversion (higher to lower bitwidth)
"""
def __init__(self, in_pspec, out_pspec):
super().__init__(in_pspec, "downconvert")
def ispec(self):
- return FPADDBaseData(self.in_pspec)
+ return FPBaseData(self.in_pspec)
def ospec(self):
- return FPAddStage1Data(self.out_pspec, e_extra=True)
+ return FPPostCalcData(self.out_pspec, e_extra=True)
def elaborate(self, platform):
m = Module()
comb = m.d.comb
+ print("in_width out", self.in_pspec.width, self.out_pspec.width)
- #m.submodules.sc_out_z = self.o.z
+ # here we make room (in temporary constants / ospec) for extra
+ # bits in the exponent, at the size of the *incoming* number
+ # bitwidth. in this way it is possible to detect, in the
+ # *outgoing* number, if the exponent is too large and needs
+ # adjustment. otherwise we have to mess about with all sorts
+ # of width-detection and the normalisation, special cases etc.
+ # all become horribly complicated.
- # decode: XXX really should move to separate stage
- print("in_width out", self.in_pspec.width,
- self.out_pspec.width)
a1 = FPNumBaseRecord(self.in_pspec.width, False)
print("a1", a1.width, a1.rmw, a1.e_width, a1.e_start, a1.e_end)
m.submodules.sc_decode_a = a1 = FPNumDecode(None, a1)
comb += exp_sub_n126.eq(a1.e - N126)
comb += exp_gt127.eq(a1.e > P127)
+ # bypass (always enabled except for normalisation, below)
+ comb += self.o.out_do_z.eq(1)
+
# if a zero, return zero (signed)
with m.If(a1.exp_n127):
comb += self.o.z.zero(a1.s)
- comb += self.o.out_do_z.eq(1)
# if a range outside z's min range (-126)
with m.Elif(exp_sub_n126 < 0):
comb += self.o.of.guard.eq(a1.m[ms-1])
comb += self.o.of.round_bit.eq(a1.m[ms-2])
comb += self.o.of.sticky.eq(a1.m[:ms-2].bool())
- comb += self.o.of.m0.eq(a1.m[ms]) # bit of a1
+ comb += self.o.of.m0.eq(a1.m[ms]) # LSB bit of a1
comb += self.o.z.s.eq(a1.s)
comb += self.o.z.e.eq(a1.e)
comb += self.o.z.m.eq(a1.m[-self.o.z.rmw-1:])
comb += self.o.z.m[-1].eq(1)
+ # normalisation required
+ comb += self.o.out_do_z.eq(0)
+
# if a is inf return inf
with m.Elif(a1.is_inf):
comb += self.o.z.inf(a1.s)
- comb += self.o.out_do_z.eq(1)
# if a is NaN return NaN
with m.Elif(a1.is_nan):
comb += self.o.z.nan(0)
- comb += self.o.out_do_z.eq(1)
# if a mantissa greater than 127, return inf
with m.Elif(exp_gt127):
print("inf", self.o.z.inf(a1.s))
comb += self.o.z.inf(a1.s)
- comb += self.o.out_do_z.eq(1)
# ok after all that, anything else should fit fine (whew)
with m.Else():
mo = Signal(self.o.z.m_width-1)
comb += mo.eq(a1.m[ms:me])
with m.If(self.o.of.roundz):
- with m.If((~mo == 0)): # all 1s
+ with m.If((mo.all())): # mantissa-out is all 1s
comb += self.o.z.create(a1.s, a1.e+1, mo+1)
with m.Else():
comb += self.o.z.create(a1.s, a1.e, mo+1)
with m.Else():
comb += self.o.z.create(a1.s, a1.e, a1.m[-self.o.z.rmw-1:])
- comb += self.o.out_do_z.eq(1)
# copy the context (muxid, operator)
comb += self.o.oz.eq(self.o.z.v)
projects / ieee754fpu.git / blobdiff