From 9242ee2c8f892d95ac15b09fc260f820f127ec8d Mon Sep 17 00:00:00 2001
From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Fri, 28 Jun 2019 06:47:47 +0100
Subject: [PATCH] add cookie-cut div0.py pipeline stage class

---
 src/ieee754/fpdiv/div0.py | 105 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 105 insertions(+)
 create mode 100644 src/ieee754/fpdiv/div0.py

diff --git a/src/ieee754/fpdiv/div0.py b/src/ieee754/fpdiv/div0.py
new file mode 100644
index 00000000..796e6c29
--- /dev/null
+++ b/src/ieee754/fpdiv/div0.py
@@ -0,0 +1,105 @@
+"""IEEE754 Floating Point Divider 
+
+Relevant bugreport: http://bugs.libre-riscv.org/show_bug.cgi?id=99
+"""
+
+from nmigen import Module, Signal, Cat, Elaboratable
+from nmigen.cli import main, verilog
+
+from ieee754.fpcommon.fpbase import FPNumBaseRecord
+from ieee754.fpcommon.fpbase import FPState
+from ieee754.fpcommon.denorm import FPSCData
+
+
+class FPDivStage0Data:
+
+    def __init__(self, width, id_wid):
+        self.z = FPNumBaseRecord(width, False)
+        self.out_do_z = Signal(reset_less=True)
+        self.oz = Signal(width, reset_less=True)
+
+        # TODO: here is where Q and R would be put, and passed
+        # down to Stage1 processing.
+
+        mw = (self.z.m_width)*2 - 1 + 3 # sticky/round/guard bits + (2*mant) - 1
+        self.product = Signal(mw, reset_less=True)
+
+        self.mid = Signal(id_wid, reset_less=True)
+
+    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.product.eq(i.product), self.mid.eq(i.mid)]
+
+
+class FPDivStage0Mod(Elaboratable):
+
+    def __init__(self, width, id_wid):
+        self.width = width
+        self.id_wid = id_wid
+        self.i = self.ispec()
+        self.o = self.ospec()
+
+    def ispec(self):
+        return FPSCData(self.width, self.id_wid, False)
+
+    def ospec(self):
+        return FPDivStage0Data(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.div0 = self
+        m.d.comb += self.i.eq(i)
+
+    def elaborate(self, platform):
+        m = Module()
+
+        # XXX TODO, actual DIV code here.  this class would be
+        # "step one" which takes the pre-normalised data and
+        # *begins* the processing phase (enters the massive DIV
+        # pipeline chain)
+
+        # store intermediate tests (and zero-extended mantissas)
+        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 += [
+                     am0.eq(Cat(self.i.a.m, 0)),
+                     bm0.eq(Cat(self.i.b.m, 0))
+                    ]
+        # same-sign (both negative or both positive) div mantissas
+        with m.If(~self.i.out_do_z):
+            m.d.comb += [self.o.z.e.eq(self.i.a.e + self.i.b.e + 1),
+                         # TODO: no, not product, first stage Q and R etc. etc.
+                         # go here.
+                         self.o.product.eq(am0 * bm0 * 4),
+                         self.o.z.s.eq(self.i.a.s ^ self.i.b.s)
+                ]
+
+        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 FPDivStage0(FPState):
+    """ First stage of div.  
+    """
+
+    def __init__(self, width, id_wid):
+        FPState.__init__(self, "divider_0")
+        self.mod = FPDivStage0Mod(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 div0+div1)
+        m.d.sync += self.o.eq(self.mod.o)
+
+    def action(self, m):
+        m.next = "divider_1"
-- 
2.30.2