From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Sat, 15 Feb 2020 14:30:38 +0000 (+0000)
Subject: clip shift amount
X-Git-Tag: ls180-24jan2020~156
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=941156a34b3d02f8571b28fc6d54efb5bca6f666;p=ieee754fpu.git

clip shift amount
---

diff --git a/src/ieee754/part_shift/part_shift_dynamic.py b/src/ieee754/part_shift/part_shift_dynamic.py
index d991e5f8..ccfc5d04 100644
--- a/src/ieee754/part_shift/part_shift_dynamic.py
+++ b/src/ieee754/part_shift/part_shift_dynamic.py
@@ -120,13 +120,16 @@ class PartitionedDynamicShift(Elaboratable):
             # the partition mask, this calculates that with a mux
             # chain
 
-            # This computes the partial results table
+            # This computes the partial results table.  note that
+            # the shift amount is truncated because there's no point
+            # trying to shift data by 64 bits if the result width
+            # is only 8.
             shifter = Signal(shiftbits, name="shifter%d" % i,
                           reset_less=True)
-            #with m.If(element > shiftbits):
-            #    comb += shifter.eq(shiftbits)
-            #with m.Else():
-            #    comb += shifter.eq(element)
+            with m.If(element > shiftbits):
+                comb += shifter.eq(shiftbits)
+            with m.Else():
+                comb += shifter.eq(element)
             comb += shifter.eq(element)
             partial = Signal(reswid, name="partial%d" % i, reset_less=True)
             comb += partial.eq(a_intervals[i] << shifter)