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  */
int_sqrt(unsigned long x)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);
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  */
int_sqrt64(u64 x)48 u32 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) & ~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 }
69 EXPORT_SYMBOL(int_sqrt64);
70 #endif
71