Initial data commit

Task/Bitwise-operations/Python/bitwise-operations-4.py

@@ -0,0 +1,41 @@
+def bitstr(n, width=None):
+   """return the binary representation of n as a string and
+      optionally zero-fill (pad) it to a given length
+   """
+   result = list()
+   while n:
+      result.append(str(n%2))
+      n = int(n/2)
+   if (width is not None) and len(result) < width:
+      result.extend(['0'] * (width - len(result)))
+   result.reverse()
+   return ''.join(result)
+
+def mask(n):
+   """Return a bitmask of length n (suitable for masking against an
+      int to coerce the size to a given length)
+   """
+   if n >= 0:
+       return 2**n - 1
+   else:
+       return 0
+
+def rol(n, rotations=1, width=8):
+    """Return a given number of bitwise left rotations of an integer n,
+       for a given bit field width.
+    """
+    rotations %= width
+    if rotations < 1:
+        return n
+    n &= mask(width) ## Should it be an error to truncate here?
+    return ((n << rotations) & mask(width)) | (n >> (width - rotations))
+
+def ror(n, rotations=1, width=8):
+    """Return a given number of bitwise right rotations of an integer n,
+       for a given bit field width.
+    """
+    rotations %= width
+    if rotations < 1:
+        return n
+    n &= mask(width)
+    return (n >> rotations) | ((n << (width - rotations)) & mask(width))