https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88156
--- Comment #6 from rguenther at suse dot de <rguenther at suse dot de> --- On Fri, 23 Nov 2018, xantares09 at hotmail dot com wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88156 > > --- Comment #2 from xantares09 at hotmail dot com --- > Thanks for the quick reply. > > On mingw __WCHAR_TYPE__ expands to short unsigned int: > > $ x86_64-w64-mingw32-gcc -E main.c > ... > # 3 "main.cxx" > int string_hash(const short unsigned int* data) { > > > On x86_64-linux it expands to int: > $ gcc -E main.c > ... > # 3 "main.c" > int string_hash(const int* data) { Ok, but then we have h = (h * 7) ^ *data; which is on mingw h = (h * 7) ^ (int)*data zero-extending *data. This means the XOR can never change the sign of h. Likewise h * 7 can never make h negative because h is initially zero and the operation would need to overflow to become negative but that would invoke undefined behavior. Thus the bug is INVALID. You can use -fwrapv or make h unsigned int to fix this (and adjust the h < 0 test to (int)h < 0).
