From 48c84a9dcb92896ed84cc29fa5202302b9218baa Mon Sep 17 00:00:00 2001
From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Mon, 4 Mar 2019 04:13:02 +0000
Subject: [PATCH] use MultiShiftRMerge module instead of shift_down_multi
 function

---
 src/add/fpbase.py                | 16 +++++++++++-----
 src/add/nmigen_add_experiment.py | 19 +++++++++++++++----
 src/add/test_add.py              |  1 +
 3 files changed, 27 insertions(+), 9 deletions(-)

diff --git a/src/add/fpbase.py b/src/add/fpbase.py
index 4430f9c6..dd2179f5 100644
--- a/src/add/fpbase.py
+++ b/src/add/fpbase.py
@@ -188,11 +188,13 @@ class MultiShiftRMerge:
     """ shifts down (right) and merges lower bits into m[0].
         m[0] is the "sticky" bit, basically
     """
-    def __init__(self, width):
-        self.smax = int(log(width) / log(2))
+    def __init__(self, width, s_max=None):
+        if s_max is None:
+            s_max = int(log(width) / log(2))
+        self.smax = s_max
         self.m = Signal(width, reset_less=True)
         self.inp = Signal(width, reset_less=True)
-        self.diff = Signal(self.smax, reset_less=True)
+        self.diff = Signal(s_max, reset_less=True)
         self.width = width
 
     def elaborate(self, platform):
@@ -202,12 +204,16 @@ class MultiShiftRMerge:
         m_mask = Signal(self.width, reset_less=True)
         smask = Signal(self.width, reset_less=True)
         stickybit = Signal(reset_less=True)
+        maxslen = Signal(self.smax, reset_less=True)
+        maxsleni = Signal(self.smax, reset_less=True)
 
         sm = MultiShift(self.width-1)
         m0s = Const(0, self.width-1)
         mw = Const(self.width-1, len(self.diff))
-        maxslen = Mux(self.diff > mw, mw, self.diff)
-        maxsleni = mw - maxslen
+        m.d.comb += [maxslen.eq(Mux(self.diff > mw, mw, self.diff)),
+                     maxsleni.eq(Mux(self.diff > mw, 0, mw-self.diff)),
+                    ]
+
         m.d.comb += [
                 # shift mantissa by maxslen, mask by inverse
                 rs.eq(sm.rshift(self.inp[1:], maxslen)),
diff --git a/src/add/nmigen_add_experiment.py b/src/add/nmigen_add_experiment.py
index ee595969..73e1d7a8 100644
--- a/src/add/nmigen_add_experiment.py
+++ b/src/add/nmigen_add_experiment.py
@@ -7,6 +7,7 @@ from nmigen.lib.coding import PriorityEncoder
 from nmigen.cli import main, verilog
 
 from fpbase import FPNumIn, FPNumOut, FPOp, Overflow, FPBase, FPNumBase
+from fpbase import MultiShiftRMerge
 #from fpbase import FPNumShiftMultiRight
 
 class FPState(FPBase):
@@ -366,15 +367,25 @@ class FPAddAlignSingleMod:
         # temporary (muxed) input and output to be shifted
         t_inp = FPNumBase(self.width)
         t_out = FPNumIn(None, self.width)
+        espec = (len(self.in_a.e), True)
+        msr = MultiShiftRMerge(self.in_a.m_width, espec)
         m.submodules.align_t_in = t_inp
         m.submodules.align_t_out = t_out
+        m.submodules.multishift_r = msr
 
-        ediff = Signal((len(self.in_a.e), True), reset_less=True)
-        ediffr = Signal((len(self.in_a.e), True), reset_less=True)
-        tdiff = Signal((len(self.in_a.e), True), reset_less=True)
+        ediff = Signal(espec, reset_less=True)
+        ediffr = Signal(espec, reset_less=True)
+        tdiff = Signal(espec, reset_less=True)
         elz = Signal(reset_less=True)
         egz = Signal(reset_less=True)
 
+        # connect multi-shifter to t_inp/out mantissa (and tdiff)
+        m.d.comb += msr.inp.eq(t_inp.m)
+        m.d.comb += msr.diff.eq(tdiff)
+        m.d.comb += t_out.m.eq(msr.m)
+        m.d.comb += t_out.e.eq(t_inp.e + tdiff)
+        m.d.comb += t_out.s.eq(t_inp.s)
+
         m.d.comb += ediff.eq(self.in_a.e - self.in_b.e)
         m.d.comb += ediffr.eq(self.in_b.e - self.in_a.e)
         m.d.comb += elz.eq(self.in_a.e < self.in_b.e)
@@ -384,7 +395,7 @@ class FPAddAlignSingleMod:
         m.d.comb += self.out_a.copy(self.in_a)
         m.d.comb += self.out_b.copy(self.in_b)
         # only one shifter (muxed)
-        m.d.comb += t_out.shift_down_multi(tdiff, t_inp)
+        #m.d.comb += t_out.shift_down_multi(tdiff, t_inp)
         # exponent of a greater than b: shift b down
         with m.If(egz):
             m.d.comb += [t_inp.copy(self.in_b),
diff --git a/src/add/test_add.py b/src/add/test_add.py
index 1f143beb..dece8961 100644
--- a/src/add/test_add.py
+++ b/src/add/test_add.py
@@ -11,6 +11,7 @@ from unit_test_single import (get_mantissa, get_exponent, get_sign, is_nan,
                                 run_edge_cases, run_corner_cases)
 
 def testbench(dut):
+    yield from check_case(dut, 0x36093399, 0x7f6a12f1, 0x7f6a12f1)
     yield from check_case(dut, 0x006CE3EE, 0x806CE3EC, 0x00000002)
     yield from check_case(dut, 0x00000047, 0x80000048, 0x80000001)
     yield from check_case(dut, 0x000116C2, 0x8001170A, 0x80000048)
-- 
2.30.2