C++ fast division/mod by 10^x

Question

In my program I use a lot of integer division by 10^x and integer mod function of power 10.

For example:

unsigned __int64 a = 12345;
a = a / 100;
...         


        

Answer 1

In fact you don't need to do anything. The compiler is smart enough to optimize multiplications/divisions with constants. You can find many examples here

• Why does GCC use multiplication by a strange number in implementing integer division?
• Divide by 10 using bit shifts?
• Fast Division on GCC/ARM

You can even do a fast divide by 5 then shift right by 1