[cfe-dev] sanitize float-cast-overflow false positive with 255.5 to uint8_t?

[Sean McBride]

Hi all,

Consider this C++:

-------------------
#include <stdint.h>

int main (void)
{
  double d = 255.5;
  uint8_t c = (uint8_t)d;
  
  return c;
}
-------------------

then:

$ clang++ -fsanitize=float-cast-overflow test.cxx

runtime error: value 255.5 is outside the range of representable values of type 'unsigned char'

Now, I'm no language lawyer, but the standard seems to say "An rvalue of a floating point type can be converted to an rvalue of an integer type. The conversion truncates; that is, the fractional part is discarded. The behavior is undefined if the ***truncated*** value cannot be represented in the destination type."  (emphasis mine)

So is clang wrong to complain here?

Thanks,

-- 
____________________________________________________________
Sean McBride, B. Eng                 sean at rogue-research.com
Rogue Research                        www.rogue-research.com 
Mac Software Developer              Montréal, Québec, Canada