From a8f666d99a34a7c08e05834bda151b62f0c752a6 Mon Sep 17 00:00:00 2001 From: Luke Kenneth Casson Leighton Date: Sun, 25 Aug 2019 16:51:24 +0100 Subject: [PATCH] remove m.If/Elif from fpdiv specialcases --- src/ieee754/fpdiv/specialcases.py | 88 +++++++++++++++++++------------ 1 file changed, 55 insertions(+), 33 deletions(-) diff --git a/src/ieee754/fpdiv/specialcases.py b/src/ieee754/fpdiv/specialcases.py index 92eec062..b8698c08 100644 --- a/src/ieee754/fpdiv/specialcases.py +++ b/src/ieee754/fpdiv/specialcases.py @@ -9,7 +9,7 @@ Relevant bugreports: * http://bugs.libre-riscv.org/show_bug.cgi?id=44 """ -from nmigen import Module, Signal +from nmigen import Module, Signal, Cat, Mux from nmigen.cli import main, verilog from math import log @@ -41,8 +41,9 @@ class FPDIVSpecialCasesMod(PipeModBase): comb = m.d.comb # decode: XXX really should move to separate stage - a1 = FPNumBaseRecord(self.pspec.width, False, name="a1") - b1 = FPNumBaseRecord(self.pspec.width, False, name="b1") + 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) comb += [a1.v.eq(self.i.a), @@ -53,15 +54,42 @@ class FPDIVSpecialCasesMod(PipeModBase): # temporaries (used below) sabx = Signal(reset_less=True) # sign a xor b (sabx, get it?) - abnan = Signal(reset_less=True) - abinf = Signal(reset_less=True) + 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_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 += abnan.eq(a1.is_nan | b1.is_nan) - comb += abinf.eq(a1.is_inf & b1.is_inf) - - # default (overridden if needed) - comb += self.o.out_do_z.eq(1) + 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_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_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_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()) # select one of 3 different sets of specialcases (DIV, SQRT, RSQRT) with m.Switch(self.i.ctx.op): @@ -69,36 +97,27 @@ class FPDIVSpecialCasesMod(PipeModBase): ########## DIV ############ with m.Case(int(DP.UDivRem)): - # if a is NaN or b is NaN return NaN - with m.If(abnan): - comb += self.o.z.nan(0) + # 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 - with m.Elif(abinf): - comb += self.o.z.nan(0) - # if a is inf return inf - with m.Elif(a1.is_inf): - comb += self.o.z.inf(sabx) - # if b is inf return zero - with m.Elif(b1.is_inf): - comb += self.o.z.zero(sabx) - # if a is zero return zero (or NaN if b is zero) - with m.Elif(a1.is_zero): - comb += self.o.z.zero(sabx) # b is zero return NaN - with m.If(b1.is_zero): - comb += self.o.z.nan(0) - # if b is zero return Inf - with m.Elif(b1.is_zero): - comb += self.o.z.inf(sabx) - # Denormalised Number checks next, so pass a/b data through - with m.Else(): - comb += self.o.out_do_z.eq(0) + # 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)): @@ -123,6 +142,8 @@ class FPDIVSpecialCasesMod(PipeModBase): with m.Else(): comb += self.o.out_do_z.eq(0) + comb += self.o.oz.eq(self.o.z.v) + ########## RSQRT ############ with m.Case(int(DP.RSqrtRem)): @@ -147,8 +168,9 @@ class FPDIVSpecialCasesMod(PipeModBase): 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.oz.eq(self.o.z.v) comb += self.o.ctx.eq(self.i.ctx) return m -- 2.30.2