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/export.h>
10 #include <linux/bitops.h>
11 #include <linux/limits.h>
12 #include <linux/math.h>
13
14 /**
15 * int_sqrt - computes the integer square root
16 * @x: integer of which to calculate the sqrt
17 *
18 * Computes: floor(sqrt(x))
19 */
20 unsigned long int_sqrt(unsigned long x)
21 {
22 unsigned long b, m, y = 0;
23
24 if (x <= 1)
25 return x;
26
27 m = 1UL << (__fls(x) & ~1UL);
28 while (m != 0) {
29 b = y + m;
30 y >>= 1;
31
32 if (x >= b) {
33 x -= b;
34 y += m;
35 }
36 m >>= 2;
37 }
38
39 return y;
40 }
41 EXPORT_SYMBOL(int_sqrt);
42
43 #if BITS_PER_LONG < 64
44 /**
45 * int_sqrt64 - strongly typed int_sqrt function when minimum 64 bit input
46 * is expected.
47 * @x: 64bit integer of which to calculate the sqrt
48 */
49 u32 int_sqrt64(u64 x)
50 {
51 u64 b, m, y = 0;
52
53 if (x <= ULONG_MAX)
54 return int_sqrt((unsigned long) x);
55
56 m = 1ULL << ((fls64(x) - 1) & ~1ULL);
57 while (m != 0) {
58 b = y + m;
59 y >>= 1;
60
61 if (x >= b) {
62 x -= b;
63 y += m;
64 }
65 m >>= 2;
66 }
67
68 return y;
69 }
70 EXPORT_SYMBOL(int_sqrt64);
71 #endif
72
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