BIND 10 trac1883, updated. 400da17fc216ce60be368e20dabdca638c81b45d [1883] workaround a build failure with g++ 4.6 using a mutable variable.

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- Log -----------------------------------------------------------------
commit 400da17fc216ce60be368e20dabdca638c81b45d
Author: JINMEI Tatuya <jinmei at isc.org>
Date:   Fri Jul 6 11:07:32 2012 -0700

    [1883] workaround a build failure with g++ 4.6 using a mutable variable.
    
    see the comment in the diff for the rationale.

-----------------------------------------------------------------------

Summary of changes:
 src/lib/dns/python/pydnspp_common.h |   17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

-----------------------------------------------------------------------
diff --git a/src/lib/dns/python/pydnspp_common.h b/src/lib/dns/python/pydnspp_common.h
index 1513dd9..3cc69c4 100644
--- a/src/lib/dns/python/pydnspp_common.h
+++ b/src/lib/dns/python/pydnspp_common.h
@@ -84,17 +84,22 @@ Py_hash_t
 convertToPyHash(HashvalType val) {
     BOOST_STATIC_ASSERT(sizeof(HashvalType) <= sizeof(Py_hash_t));
 
+    // Some versions of g++ doesn't ignore the impossible case of if/else
+    // below (depending on the size of HashvalType) and triggers a false
+    // warning.
+    // To work around it we use an intermediate mutable variable.
+    // See Trac #1883 for details.
+    size_t hash_val_bits = CHAR_BIT * sizeof(HashvalType);
+
     if (sizeof(HashvalType) < sizeof(Py_hash_t)) {
-        // The original hash type has small enough.  Do trivial conversion.
-        const Py_hash_t mask = ~(static_cast<Py_hash_t>(-1) <<
-                                 (CHAR_BIT * sizeof(HashvalType)));
+        // The original hash type is small enough.  Do trivial conversion.
+        const Py_hash_t mask = ~(static_cast<Py_hash_t>(-1) << hash_val_bits);
         return (static_cast<Py_hash_t>(val) & mask);
     } else {
         // Clear the highest bit of the original hash so the conversion is
         // safe and avoids -1.
-        const HashvalType mask = ~(static_cast<HashvalType>(1) <<
-                                   (CHAR_BIT * sizeof(HashvalType) - 1));
-        BOOST_STATIC_ASSERT(mask != static_cast<HashvalType>(-1));
+        HashvalType mask = ~(static_cast<HashvalType>(1) <<
+                             (hash_val_bits - 1));
         return (val & mask);
     }
 }