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 #include <linux/bitops.h>
  11
  12 /**
  13  * int_sqrt - rough approximation to sqrt
  14  * @x: integer of which to calculate the sqrt
  15  *
  16  * A very rough approximation to the sqrt() function.
  17  */
  18 unsigned long int_sqrt(unsigned long x)
  19 {
  20         unsigned long b, m, y = 0;
  21
  22         if (x <= 1)
  23                 return x;
  24
  25         m = 1UL << (__fls(x) & ~1UL);
  26         while (m != 0) {
  27                 b = y + m;
  28                 y >>= 1;
  29
  30                 if (x >= b) {
  31                         x -= b;
  32                         y += m;
  33                 }
  34                 m >>= 2;
  35         }
  36
  37         return y;
  38 }
  39 EXPORT_SYMBOL(int_sqrt);