On 22/09/17 17:11, Jeff King wrote: > On Fri, Sep 22, 2017 at 05:05:03PM +0100, Ramsay Jones wrote: > >>> As an aside, I also see some uses of hexval() that don't appear to be >>> quite as rigorous in checking for invalid characters. A few >>> unconditionally shift the first nibble and assume that there will still >>> be high bits set. I think that's generally true for twos-complement >>> negative numbers, but isn't shifting off the left side of a signed >>> integer undefined behavior? >> >> All uses of hexval() that I can see are shifting an unsigned value. >> Have I missed something? > > Hmm. get_hex_color() does: > > unsigned int val; > val = (hexval(in[0]) << 4) | hexval(in[1])); > > Isn't that shifting the signed return value of hexval(), and then > converting it to unsigned afterwards?
Err ... no. the return value of hexval() is *unsigned int*. (which is kinda the point!) > I've been confused by C's integer conversion rules before, though, so > perhaps I'm wrong. > > I think if this function is fed an empty string that it will also read > past the end of the buffer for in[1]. It shouldn't matter, since the NUL > in in[0] would cause us to return an error regardless, but it's still > undefined behavior. Correct. > In fact, this whole function is just hex2chr() implemented badly. Who is > responsible for this terrible code? ;) ;-) ATB, Ramsay Jones
