John Fine <johnsfine@xxxxxxxxxxx> writes: > When an unsigned int is passed or returned in a 64-bit register, does > either the C or C++ ABI specify that the top half of the register > contain zero? There are threads on the subject at http://groups.google.com/group/ia32-abi/browse_thread/thread/f47e0106b21d9269 http://gcc.gnu.org/ml/gcc/2008-01/msg00052.html Short answer: the ABI does not specify, and gcc's behaviour has recently changed. Ian
