Hi, I'm generalizing my fixed point class and have come across a few design decisions. 1. Return type of additive arithmetic operation between integers and fixed points Example: a 16 bit integer is added to a 16 bit fixed point with 8 bit fraction. I see three possible return types: 16 bit integer, 16:8 fixed point and promoted 32:8 fixed point If return type is 16 bit integer, the fraction is lost. Clearly not an option. If return type is 16:8 fixed point overflow is possible. A return type of 32:8 would eliminate overflow, but promotion quickly becomes problematic for larger integer types, lets say a 32 bit integer added to a fixed point. In that case we would need a 64 bit integer which could cripple performance on many systems. Another problem with promotion is that the arithmetic expression typically would be in a context where the expression is assigned to a fixed point of the type present in the expression. In that case we have an overflow problem again. I think I favor keeping the return type in 16:8. The user would then have to use an explicit cast to avoid overflow. 2. Return type of additive arithmetic operation between float and fixed points Example: fixed_point<int, 16>(10.5) + 5.5f (integer is representing type, 16 bit is the bit reserved for the fraction) What would you expect the return type to be? I think I favor returning a float. The accuracy of the fixed point is compromised anyway. 3. Return type of additive arithmetic operation between different fixed point types Example: fixed_point<int, 16>(10.5) + fixed_point<int, 8>(10.5) Like in case 1 there is the choice between losing precision, risking overflow or promoting (ex. to fixed_point<boost::int_t<16 + 8>::fast, 16>) I think I favor to simply disallow implicit arithmetic between different fixed point types. This would require the user to cast either type. The problem with that choice is less transparent use of the fixed_point type, since changing a type could break existing code where the previous type was in a valid arithmetic operation with another fixed point type. 4. Similar problems exist for multiplication and division If a fixed_point is multiplied with an integer there is a risk of overflow. If a fixed_point is multiplied with another fixed_point there is a risk of overflow and precision will be lost. If a fixed_point is divided by an integer there is a risk of loss of precision. If a fixed_point or integer is divided by another fixed_point there is a risk of overflow and loss of precision. Soren