On 01/02/2016 06:26 AM, Vincent Diepeveen wrote:
Assuming function f() has been defined Comparing 2 different types is undefined in C. Note that compilers that optimize better than GCC, say intel c++ which is 10% - 30% faster for many of my codes, statistical odds it goes wrong is higher than GCC. In assembler it could for example XOR just register ah, which is a 8 bits register and then further you compare register aex with another value.
This description and the mention of Intel C++ reminds of a coding bug we would occasionally run into with the bi-endian ICC. The bug was caused by inconsistent function declarations (e.g., by accidentally redeclaring a function defined to return a big-endian bool in a little-endian region, effectively lying to the compiler about the endianity of the return type). Even when the function returned true, the caller would read it as false. This was because the return value was stored by the called function in the high (big-endian) byte and extracted by the caller from the low (little-endian) byte of the register. The same problem can happen even without mixing big- and little endian code, but the bi-endian ICC makes it easier and tricky to debug. In both cases, the behavior of such programs is undefined, but it has nothing to do with comparing values of different types and everything with the mismatched function declarations. Martin
