fix MultiShift* classes to correctly calculate shift-amount bit width

diff --git a/src/ieee754/fpcommon/fpbase.py b/src/ieee754/fpcommon/fpbase.py
index f3e68fe6add8882507a92c63aa3604886cf3726e..ab6cc705dc5ae7e0113cd31736efca9bd0420676 100644 (file)
--- a/src/ieee754/fpcommon/fpbase.py
+++ b/src/ieee754/fpcommon/fpbase.py
@@ -8,7 +8,7 @@ Copyright (C) 2019,2022 Jacob Lifshay <programmerjake@gmail.com>
 
 from nmigen import (Signal, Cat, Const, Mux, Module, Elaboratable, Array,
                     Value, Shape)
-from math import log
+from nmigen.utils import bits_for
 from operator import or_
 from functools import reduce
 
@@ -526,11 +526,11 @@ class TestFPFormat(unittest.TestCase):
         self.assertEqual(i, True)
 
 
-class MultiShiftR:
+class MultiShiftR(Elaboratable):
 
     def __init__(self, width):
         self.width = width
-        self.smax = int(log(width) / log(2))
+        self.smax = bits_for(width - 1)
         self.i = Signal(width, reset_less=True)
         self.s = Signal(self.smax, reset_less=True)
         self.o = Signal(width, reset_less=True)
@@ -554,7 +554,7 @@ class MultiShift:
 
     def __init__(self, width):
         self.width = width
-        self.smax = int(log(width) / log(2))
+        self.smax = bits_for(width - 1)
 
     def lshift(self, op, s):
         res = op << s
@@ -808,7 +808,7 @@ class MultiShiftRMerge(Elaboratable):
 
     def __init__(self, width, s_max=None):
         if s_max is None:
-            s_max = int(log(width) / log(2))
+            s_max = bits_for(width - 1)
         self.smax = Shape.cast(s_max)
         self.m = Signal(width, reset_less=True)
         self.inp = Signal(width, reset_less=True)