lib/int_sqrt.c

   1 /*
   2  * Copyright (C) 2013 Davidlohr Bueso <davidlohr.bueso@hp.com>
   3  *
   4  *  Based on the shift-and-subtract algorithm for computing integer
   5  *  square root from Guy L. Steele.
   6  */
   7
   8 #include <linux/kernel.h>
   9 #include <linux/export.h>
  10
  11 /**
  12  * int_sqrt - rough approximation to sqrt
  13  * @x: integer of which to calculate the sqrt
  14  *
  15  * A very rough approximation to the sqrt() function.
  16  */
  17 unsigned long int_sqrt(unsigned long x)
  18 {
  19         unsigned long b, m, y = 0;
  20
  21         if (x <= 1)
  22                 return x;
  23
  24         m = 1UL << (BITS_PER_LONG - 2);
  25         while (m != 0) {
  26                 b = y + m;
  27                 y >>= 1;
  28
  29                 if (x >= b) {
  30                         x -= b;
  31                         y += m;
  32                 }
  33                 m >>= 2;
  34         }
  35
  36         return y;
  37 }
  38 EXPORT_SYMBOL(int_sqrt);