Is multiplication and division using shift operators in C actually faster?

Question

Multiplication and division can be achieved using bit operators, for example i*2 = i<<1 i*3 = (i<<1) + i; i*10 = (i<<3) + (i<<1) and so on. Is it actually faster to use say `(i<<3)+(i<<1)` to multiply with 10 than using `i*10` directly? Is there any sort of input that can't be multiplied or divided in this way?

Answer 1

I would ask why you'd want to code your code this way as part of my response. Today's compilers are super efficient, and would generate the necessary code to make the multiplication and division as fast as possible. While your code might take advantage of bit manipulation, I doubt it would that much faster than what the compiler could optimize.

The other thing to consider is readability. You want your code to be readable, for others who may use your code or even yourself if you come back at a later time. Reading "value = x * 10;" is far more easy to figure out than "value = x << 3 + x << 1;" When you've written enough code, obfuscation is something you want to avoid.