use Mux instead of m.If/Elif on add sign

[ieee754fpu.git] / src / ieee754 / fpadd / add0.py

diff --git a/src/ieee754/fpadd/add0.py b/src/ieee754/fpadd/add0.py
index 76790fe22bbd4d48220e98b78d694b8ef2567180..c3300a60410d659a9307638312cfbe175f69222e 100644 (file)
--- a/src/ieee754/fpadd/add0.py
+++ b/src/ieee754/fpadd/add0.py
@@ -1,113 +1,65 @@
-# IEEE Floating Point Adder (Single Precision)
-# Copyright (C) Jonathan P Dawson 2013
-# 2013-12-12
+"""IEEE754 Floating Point Adder Pipeline
 
-from nmigen import Module, Signal, Cat, Elaboratable
-from nmigen.cli import main, verilog
-
-from fpbase import FPNumBase
-from fpbase import FPState
-from fpcommon.denorm import FPSCData
+Copyright (C) 2019 Luke Kenneth Casson Leighton <lkcl@lkcl.net>
 
+"""
 
-class FPAddStage0Data:
+from nmigen import Module, Signal, Cat, Mux
+from nmigen.cli import main, verilog
 
-    def __init__(self, width, id_wid):
-        self.z = FPNumBase(width, False)
-        self.out_do_z = Signal(reset_less=True)
-        self.oz = Signal(width, reset_less=True)
-        self.tot = Signal(self.z.m_width + 4, reset_less=True)
-        self.mid = Signal(id_wid, reset_less=True)
+from nmutil.pipemodbase import PipeModBase
 
-    def eq(self, i):
-        return [self.z.eq(i.z), self.out_do_z.eq(i.out_do_z), self.oz.eq(i.oz),
-                self.tot.eq(i.tot), self.mid.eq(i.mid)]
+from ieee754.fpcommon.denorm import FPSCData
+from ieee754.fpcommon.getop import FPPipeContext
+from ieee754.fpadd.datastruct import FPAddStage0Data
 
 
-class FPAddStage0Mod(Elaboratable):
+class FPAddStage0Mod(PipeModBase):
 
-    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, "add0")
 
     def ispec(self):
-        return FPSCData(self.width, self.id_wid)
+        return FPSCData(self.pspec, True)
 
     def ospec(self):
-        return FPAddStage0Data(self.width, self.id_wid)
-
-    def process(self, i):
-        return self.o
-
-    def setup(self, m, i):
-        """ links module to inputs and outputs
-        """
-        m.submodules.add0 = self
-        m.d.comb += self.i.eq(i)
+        return FPAddStage0Data(self.pspec)
 
     def elaborate(self, platform):
         m = Module()
-        m.submodules.add0_in_a = self.i.a
-        m.submodules.add0_in_b = self.i.b
-        m.submodules.add0_out_z = self.o.z
+        comb = m.d.comb
 
         # store intermediate tests (and zero-extended mantissas)
         seq = Signal(reset_less=True)
         mge = Signal(reset_less=True)
         am0 = Signal(len(self.i.a.m)+1, reset_less=True)
         bm0 = Signal(len(self.i.b.m)+1, reset_less=True)
-        m.d.comb += [seq.eq(self.i.a.s == self.i.b.s),
-                     mge.eq(self.i.a.m >= self.i.b.m),
-                     am0.eq(Cat(self.i.a.m, 0)),
-                     bm0.eq(Cat(self.i.b.m, 0))
-                    ]
         # same-sign (both negative or both positive) add mantissas
-        with m.If(~self.i.out_do_z):
-            m.d.comb += self.o.z.e.eq(self.i.a.e)
-            with m.If(seq):
-                m.d.comb += [
-                    self.o.tot.eq(am0 + bm0),
-                    self.o.z.s.eq(self.i.a.s)
-                ]
-            # a mantissa greater than b, use a
-            with m.Elif(mge):
-                m.d.comb += [
-                    self.o.tot.eq(am0 - bm0),
-                    self.o.z.s.eq(self.i.a.s)
+        comb += [seq.eq(self.i.a.s == self.i.b.s),
+                 mge.eq(self.i.a.m >= self.i.b.m),
+                 am0.eq(Cat(self.i.a.m, 0)),
+                 bm0.eq(Cat(self.i.b.m, 0))
                 ]
-            # b mantissa greater than a, use b
-            with m.Else():
-                m.d.comb += [
-                    self.o.tot.eq(bm0 - am0),
-                    self.o.z.s.eq(self.i.b.s)
+        comb += self.o.z.e.eq(self.i.a.e)
+        comb += self.o.z.s.eq(Mux(seq | mge, self.i.a.s, self.i.b.s))
+        with m.If(seq):
+            comb += [
+                self.o.tot.eq(am0 + bm0),
             ]
+        # a mantissa greater than b, use a
+        with m.Elif(mge):
+            comb += [
+                self.o.tot.eq(am0 - bm0),
+            ]
+        # b mantissa greater than a, use b
+        with m.Else():
+            comb += [
+                self.o.tot.eq(bm0 - am0),
+        ]
 
-        m.d.comb += self.o.oz.eq(self.i.oz)
-        m.d.comb += self.o.out_do_z.eq(self.i.out_do_z)
-        m.d.comb += self.o.mid.eq(self.i.mid)
-        return m
-
-
-class FPAddStage0(FPState):
-    """ First stage of add.  covers same-sign (add) and subtract
-        special-casing when mantissas are greater or equal, to
-        give greatest accuracy.
-    """
-
-    def __init__(self, width, id_wid):
-        FPState.__init__(self, "add_0")
-        self.mod = FPAddStage0Mod(width)
-        self.o = self.mod.ospec()
-
-    def setup(self, m, i):
-        """ links module to inputs and outputs
-        """
-        self.mod.setup(m, i)
-
-        # NOTE: these could be done as combinatorial (merge add0+add1)
-        m.d.sync += self.o.eq(self.mod.o)
+        # pass-through context
+        comb += self.o.oz.eq(self.i.oz)
+        comb += self.o.out_do_z.eq(self.i.out_do_z)
+        comb += self.o.ctx.eq(self.i.ctx)
 
-    def action(self, m):
-        m.next = "add_1"
+        return m