Wei, Wanxia wrote: > My C program is a local search algorithm for solving SAT (Satisfiability problem). The > following is a brief description of this program. > > This program uses random integers to generate an initial assignment to a SAT instance. > Then, it chooses a variable by using a heuristic and then flips this variable (flip > means to change the value of a variable from 0 to 1 or from 1 to 0) in each search > step. After many search steps, if the assignment satisfies the instance, this program > stops. If the assignment still does not satisfy the instance after many search steps, > this program stops after a predefined number of search steps. The number of search > steps is what I call performance in my previous e-mail. In addition, this program uses > both static and dynamic allocations. > > When I ran the two executables with different options on some SAT instances, they have > different flip numbers (the parameters for these two executables are the same. For > example, I use the same seed for them to generate initial assignments). I ran the > executable generated by using “gcc -m32 –O3 –lm” on a wide range of instance on > different servers for more than 1 year but I never got any errors (such as core dump). Well, this is hard. If your program behaves differently when -fno-strict-aliasing is used then it's very likely that, yes, your program has a bug. But for me to explain what -fno-strict-aliasing does requires you to have a fairly good understanding of the C language. There's a fairly good explanation at http://www.cellperformance.com/mike_acton/2006/06/understanding_strict_aliasing.html In summary, "Dereferencing a cast of a variable from one type of pointer to a different type is _usually_ in violation of the strict aliasing rule." Andrew.
