On Friday 11 June 2010 21:37:29 Dag-Erling Smørgrav wrote: > Ulrich Spörlein <[email protected]> writes: >> optimizing compilers have a tendency to remove assignments that have >> no side effects. The code in sys/crypto/sha2/sha2.c is doing a lot >> of zeroing variables, which is however optimized away. [...] Is >> there a canonical way to zero those variables and should we use them >> (memset perhaps? what are the performance implications?) > > If you stick these variables in a struct, you can memset the struct > to zero them; if there are many of them, it may be faster than > zeroing them individually. > > Alternatively, you can use something like this: > > #define FORCE_ASSIGN(type, var, value) \ > *(volatile type *)&(var) = (value)
memset can be optimised away as well. The only way is to declare those variables volatile. None of the assignments below are removed for instance: volatile int a = 0; a = 1; a = 2; _______________________________________________ [email protected] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-current To unsubscribe, send any mail to "[email protected]"
