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 - computes the integer square root
15 * @x: integer of which to calculate the sqrt
16 *
17 * Computes: floor(sqrt(x))
18 */
19unsigned 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}
40EXPORT_SYMBOL(int_sqrt);
41
42#if BITS_PER_LONG < 64
43/**
44 * int_sqrt64 - strongly typed int_sqrt function when minimum 64 bit input
45 * is expected.
46 * @x: 64bit integer of which to calculate the sqrt
47 */
48u32 int_sqrt64(u64 x)
49{
50 u64 b, m, y = 0;
51
52 if (x <= ULONG_MAX)
53 return int_sqrt((unsigned long) x);
54
55 m = 1ULL << ((fls64(x) - 1) & ~1ULL);
56 while (m != 0) {
57 b = y + m;
58 y >>= 1;
59
60 if (x >= b) {
61 x -= b;
62 y += m;
63 }
64 m >>= 2;
65 }
66
67 return y;
68}
69EXPORT_SYMBOL(int_sqrt64);
70#endif
71