Repeated integer division by a runtime constant value

Question

At some point in my program I compute an integer divisor d. From that point onward d is going to be constant.

Later in the code I will divi

Answer 1

The book "Hacker's delight" has "Chapter 10: Integer division by constant" spanning 74 pages. You can find all the code examples for free in this directory: http://www.hackersdelight.org/hdcode.htm In your case, Figs. 10-1., 10-2 and 10-3 are what you want.

The problem of dividing by a constant d is equivalent to mutiplying by c = 1/d. These algorithms calculate such a constant for you. Once you have c, you calculate the dividend as such:

int divideByMyConstant(int dividend){
  int c = MAGIC; // Given by the algorithm

  // since 1/d < 1, c is actually (1<>= k; // Manual floating point number =)

  return (int)tmp;
}