On 5/3/2024 9:52 AM, John Hubbard wrote: > On 5/3/24 1:00 AM, Ilpo Järvinen wrote: >> On Thu, 2 May 2024, John Hubbard wrote: > ... >>> diff --git a/tools/testing/selftests/resctrl/mbm_test.c b/tools/testing/selftests/resctrl/mbm_test.c >>> index d67ffa3ec63a..c873793d016d 100644 >>> --- a/tools/testing/selftests/resctrl/mbm_test.c >>> +++ b/tools/testing/selftests/resctrl/mbm_test.c >>> @@ -33,7 +33,7 @@ show_bw_info(unsigned long *bw_imc, unsigned long *bw_resc, size_t span) >>> avg_bw_imc = sum_bw_imc / 4; >>> avg_bw_resc = sum_bw_resc / 4; >>> - avg_diff = (float)labs(avg_bw_resc - avg_bw_imc) / avg_bw_imc; >>> + avg_diff = (float)(avg_bw_resc - avg_bw_imc) / avg_bw_imc; >>> avg_diff_per = (int)(avg_diff * 100); >>> ret = avg_diff_per > MAX_DIFF_PERCENT; >> >> But how are these two cases same after your change when you ended up >> removing taking the absolute value entirely? > > All of the arguments are unsigned integers, so all arithmetic results > are interpreted as unsigned, so taking the absolute value of that is > always a no-op. It does not seem as though clang can see when values have been casted. I tried to do so explicitly with a: avg_diff = labs((long)avg_bw_resc - avg_bw_imc) / (float)avg_bw_imc; But that still triggers: warning: taking the absolute value of unsigned type 'unsigned long' has no effect [-Wabsolute-value] Looks like we may need to be more explicit types and not rely on casting so much to make the compiler happy. Reinette
