blob: 6d35274170bcd6c85fa56a0b92e5696d310f7273
| 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); |
| 40 |