But you do have CPL -- that does not help? Anyway, without subtraction, you could do the very same with one additional add:
int16_t celsius2fahrenheit(int16_t c)
{
int16_t f = 0;
f += c << 1;
f += c << 2;
f += c << 3;
f += c >> 2;
f += c >> 3;
f += c >> 5;
f += 320 * 8;
f >>= 3;
return f;
}
