I do not think the conversion is specifically defined, but on my system and SirCmpwn's
the floats are rounded instead of floored, which is incorrect in this case, since
for a range from 0 to 256, any value greater or equal to 0 and less than 256 is valid.
I.e. [0;256[, or 0 <= x < 256, but if x is e.g. -0.1, then it will be rounded to 0, which
is invalid. The correct behavior would be to floor to -1.
afa2e399aa