Re: [myhdl-list] intbv wrap

[Ben <ben...@gm...>]

Hi Christopher,

I took the liberty to review and edit your patch.

As you can see, I added some tests, and removed the inclusion of the
val property. It became quite smaller ! I left your name in it as the
idea and the logic is from you.

I also moved the check from the wrap function to the constructor (no
need to check every time.).

Here is a text version, enclosed a bundle. All tests pass fine.

# HG changeset patch
# User cfelton
# Date 1303212809 18000
# Node ID 145d558e234f363c3e43e9a79ab48ad7e20d7b9b
# Parent  f77cf2c4a5894013ceb2f5c184d84136ea4f04a3
Add a wrap parameter to intbv. When set, no overflow will occur.

diff -r f77cf2c4a589 -r 145d558e234f myhdl/_intbv.py
--- a/myhdl/_intbv.py	Wed May 04 21:33:14 2011 +0200
+++ b/myhdl/_intbv.py	Tue Apr 19 06:33:29 2011 -0500
@@ -31,37 +31,46 @@
 from __builtin__ import max as maxfunc

 class intbv(object):
-    __slots__ = ('_val', '_min', '_max', '_nrbits')
+    __slots__ = ('_min', '_max', '_nrbits', '_wrap', '__val')

-    def __init__(self, val=0, min=None, max=None, _nrbits=0):
+    def __init__(self, val=0, min=None, max=None, wrap=False, _nrbits=0):
         if _nrbits:
             self._min = 0
             self._max = 2**_nrbits
+            self._nrbits = _nrbits
         else:
             self._min = min
             self._max = max
             if max is not None and min is not None:
                 if min >= 0:
-                    _nrbits = len(bin(max-1))
+                    self._nrbits = len(bin(max-1))
                 elif max <= 1:
-                    _nrbits = len(bin(min))
+                    self._nrbits = len(bin(min))
                 else:
                     # make sure there is a leading zero bit in positive numbers
-                    _nrbits = maxfunc(len(bin(max-1))+1, len(bin(min)))
+                    self._nrbits = maxfunc(len(bin(max-1))+1, len(bin(min)))
+            else:
+                self._nrbits = 0
+
+        if wrap:
+            myrange = self._nrbits**2
+            if (abs(self.min) != self.max) or ((abs(self.min) +
self.max) != myrange):
+                raise ValueError, "Cannot use wrapping if -min != max
(%d != %d)" % (-self.min, self.max)
+        self._wrap  = wrap
         if isinstance(val, (int, long)):
             self._val = val
         elif isinstance(val, StringType):
             mval = val.replace('_', '')
+            self._nrbits = len(mval)
             self._val = long(mval, 2)
-            _nrbits = len(val)
         elif isinstance(val, intbv):
             self._val = val._val
             self._min = val._min
             self._max = val._max
-            _nrbits = val._nrbits
+            self._wrap = val._wrap
+            self._nrbits = val._nrbits
         else:
             raise TypeError("intbv constructor arg should be int or string")
-        self._nrbits = _nrbits
         self._checkBounds()

     # support for the 'min' and 'max' attribute
@@ -82,6 +91,20 @@
                 raise ValueError("intbv value %s < minimum %s" %
                                  (self._val, self._min))

+    # val property
+    def _get_val(self):
+        return self.__val
+
+    def _set_val(self, pval):
+
+        if self._wrap:
+            self.__val = self.wrap(pval)
+        else:
+            self.__val = pval
+
+        self._checkBounds()
+
+    _val = property(_get_val, _set_val)

     # hash
     def __hash__(self):
@@ -433,6 +456,21 @@
         return "intbv(" + repr(self._val) + ")"


+    def wrap(self, val):
+        """ Wrap the value back to the range of the inbv
+
+        The following will check that the defined min-max is the full
+        range of the binary word.  If the full range is specified if
+        the value is outside the bounds of the range it will be adjusted
+        to the proper value in bounds.
+        """
+        myrange = 2**self._nrbits
+
+        rval = self.min + ((val +self.max) % myrange)
+
+        return rval
+
+
     def signed(self):
       ''' return integer with the signed value of the intbv instance

diff -r f77cf2c4a589 -r 145d558e234f myhdl/test/core/test_intbv.py
--- a/myhdl/test/core/test_intbv.py	Wed May 04 21:33:14 2011 +0200
+++ b/myhdl/test/core/test_intbv.py	Tue Apr 19 06:33:29 2011 -0500
@@ -576,8 +576,50 @@
                 self.assertEqual(n.max, m.max)
                 self.assertEqual(len(n), len(m))

+class TestIntbvWrap(TestCase):
+
+    def testWrap(self):
+        x = intbv(0, min=-8, max=8, wrap=True)
+        x[:] = x + 1
+        self.assertEqual(1, x)
+        x[:] = x + 2
+        self.assertEqual(3, x)
+        x[:] = x + 5
+        self.assertEqual(-8, x)
+        x[:] = x + 1
+        self.assertEqual(-7, x)
+        x[:] = x - 5
+        self.assertEqual(4, x)
+        x[:] = x - 4
+        self.assertEqual(0, x)
+        x[:] += 15
+        x[:] = x - 1
+        self.assertEqual(-2, x)
+
+    def testInit(self):
+        self.assertRaises(ValueError, intbv, 15, min=-8, max=8)
+        x = intbv(15, min=-8, max=8, wrap=True)
+        self.assertEqual(-1, x)
+
+        self.assertRaises(ValueError, intbv, 5, min=-3, max=8, wrap=True)
+        intbv(5, min=-3, max=8)


+    def testNoWrap(self):
+        x = intbv(0, min=-8, max=8, wrap=False)
+        try:
+            x[:] += 15
+            self.fail()
+        except ValueError:
+            pass
+
+        x = intbv(0, min=-8, max=8)
+        try:
+            x[:] += 15
+            self.fail()
+        except ValueError:
+            pass
+
 if __name__ == "__main__":
     unittest.main()