Allow bit rotation by more than sizeof(T)*8 bits.

Currently these functions will happily bit shift by >= sizeof(T)*8 bits.
However, this is undefined behavior, and results in unexpected results (0)
on at least one platform I've tested.

With this update, you can expect that rotate_left<uint32_t>(1, 32)==1
and rotate_right<uint32_t>(1, 32)==1.

1 files changed, 2 insertions, 0 deletions

diff --git a/src/lib/utils/rotate.h b/src/lib/utils/rotate.h
index b936521e6..8361e4705 100644
--- a/src/lib/utils/rotate.h
+++ b/src/lib/utils/rotate.h
@@ -20,6 +20,7 @@ namespace Botan {
 */
 template<typename T> inline T rotate_left(T input, size_t rot)
    {
+   rot %= 8 * sizeof(T);
    return (rot == 0) ? input : static_cast<T>((input << rot) | (input >> (8*sizeof(T)-rot)));;
    }
 
@@ -31,6 +32,7 @@ template<typename T> inline T rotate_left(T input, size_t rot)
 */
 template<typename T> inline T rotate_right(T input, size_t rot)
    {
+   rot %= 8 * sizeof(T);
    return (rot == 0) ? input : static_cast<T>((input >> rot) | (input << (8*sizeof(T)-rot)));
    }