Another stab at SF 576327: zipfile when sizeof(long) == 8

binascii_crc32():  The previous patch forced this to return the same
result across platforms.  This patch deals with that, on a 64-bit box,
the *entry* value may have "unexpected" bits in the high four bytes.

Bugfix candidate.

Modules/binascii.c

@@ -869,19 +869,25 @@ binascii_crc32(PyObject *self, PyObject *args)
 	if ( !PyArg_ParseTuple(args, "s#|l:crc32", &bin_data, &len, &crc) )
 		return NULL;
 
-	crc = crc ^ 0xFFFFFFFFUL;
-	while(len--)
+	crc = ~ crc;
+#if SIZEOF_LONG > 4
+	/* only want the trailing 32 bits */
+	crc &= 0xFFFFFFFFUL;
+#endif
+	while (len--)
 		crc = crc_32_tab[(crc ^ *bin_data++) & 0xffUL] ^ (crc >> 8);
 		/* Note:  (crc >> 8) MUST zero fill on left */
 
 	result = (long)(crc ^ 0xFFFFFFFFUL);
-	/* If long is > 32 bits, extend the sign bit.  This is one way to
-	 * ensure the result is the same across platforms.  The other way
-	 * would be to return an unbounded long, but the evidence suggests
-	 * that lots of code outside this treats the result as if it were
-	 * a signed 4-byte integer.
+#if SIZEOF_LONG > 4
+	/* Extend the sign bit.  This is one way to ensure the result is the
+	 * same across platforms.  The other way would be to return an
+	 * unbounded unsigned long, but the evidence suggests that lots of
+	 * code outside this treats the result as if it were a signed 4-byte
+	 * integer.
 	 */
 	result |= -(result & (1L << 31));
+#endif
 	return PyInt_FromLong(result);
 }