c++division

C++ Best way to get integer division and remainder

I am just wondering, if I want to divide a by b, and am interested both in the result c and the remainder (e.g. say I have number of seconds and want to split that into minutes and seconds), what is the best way to go about it?

Would it be

int c = (int)a / b;
int d = a % b;

or

int c = (int)a / b;
int d = a - b * c;

or

double tmp = a / b;
int c = (int)tmp;
int d = (int)(0.5+(tmp-c)*b);

or

maybe there is a magical function that gives one both at once?

Solution

  • On x86 the remainder is a by-product of the division itself so any half-decent compiler should be able to just use it (and not perform a div again). This is probably done on other architectures too.

    Instruction: DIV src

    Note: Unsigned division. Divides accumulator (AX) by "src". If divisor is a byte value, result is put to AL and remainder to AH. If divisor is a word value, then DX:AX is divided by "src" and result is stored in AX and remainder is stored in DX.

    int c = (int)a / b;
int d = a % b; /* Likely uses the result of the division. */