lib/int_sqrt.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (C) 2013 Davidlohr Bueso <davidlohr.bueso@hp.com>
   4  *
   5  *  Based on the shift-and-subtract algorithm for computing integer
   6  *  square root from Guy L. Steele.
   7  */
   8
   9 #include <linux/kernel.h>
  10 #include <linux/export.h>
  11 #include <linux/bitops.h>
  12
  13 /**
  14  * int_sqrt - rough approximation to sqrt
  15  * @x: integer of which to calculate the sqrt
  16  *
  17  * A very rough approximation to the sqrt() function.
  18  */
  19 unsigned long int_sqrt(unsigned long x)
  20 {
  21         unsigned long b, m, y = 0;
  22
  23         if (x <= 1)
  24                 return x;
  25
  26         m = 1UL << (__fls(x) & ~1UL);
  27         while (m != 0) {
  28                 b = y + m;
  29                 y >>= 1;
  30
  31                 if (x >= b) {
  32                         x -= b;
  33                         y += m;
  34                 }
  35                 m >>= 2;
  36         }
  37
  38         return y;
  39 }
  40 EXPORT_SYMBOL(int_sqrt);