1 // SPDX-License-Identifier: GPL-2.0 1 // SPDX-License-Identifier: GPL-2.0
2 /* 2 /*
3 * Copyright (C) 2013 Davidlohr Bueso <davidlo 3 * Copyright (C) 2013 Davidlohr Bueso <davidlohr.bueso@hp.com>
4 * 4 *
5 * Based on the shift-and-subtract algorithm 5 * Based on the shift-and-subtract algorithm for computing integer
6 * square root from Guy L. Steele. 6 * square root from Guy L. Steele.
7 */ 7 */
8 8
9 #include <linux/export.h> 9 #include <linux/export.h>
10 #include <linux/bitops.h> 10 #include <linux/bitops.h>
11 #include <linux/limits.h> 11 #include <linux/limits.h>
12 #include <linux/math.h> 12 #include <linux/math.h>
13 13
14 /** 14 /**
15 * int_sqrt - computes the integer square root 15 * int_sqrt - computes the integer square root
16 * @x: integer of which to calculate the sqrt 16 * @x: integer of which to calculate the sqrt
17 * 17 *
18 * Computes: floor(sqrt(x)) 18 * Computes: floor(sqrt(x))
19 */ 19 */
20 unsigned long int_sqrt(unsigned long x) 20 unsigned long int_sqrt(unsigned long x)
21 { 21 {
22 unsigned long b, m, y = 0; 22 unsigned long b, m, y = 0;
23 23
24 if (x <= 1) 24 if (x <= 1)
25 return x; 25 return x;
26 26
27 m = 1UL << (__fls(x) & ~1UL); 27 m = 1UL << (__fls(x) & ~1UL);
28 while (m != 0) { 28 while (m != 0) {
29 b = y + m; 29 b = y + m;
30 y >>= 1; 30 y >>= 1;
31 31
32 if (x >= b) { 32 if (x >= b) {
33 x -= b; 33 x -= b;
34 y += m; 34 y += m;
35 } 35 }
36 m >>= 2; 36 m >>= 2;
37 } 37 }
38 38
39 return y; 39 return y;
40 } 40 }
41 EXPORT_SYMBOL(int_sqrt); 41 EXPORT_SYMBOL(int_sqrt);
42 42
43 #if BITS_PER_LONG < 64 43 #if BITS_PER_LONG < 64
44 /** 44 /**
45 * int_sqrt64 - strongly typed int_sqrt functi 45 * int_sqrt64 - strongly typed int_sqrt function when minimum 64 bit input
46 * is expected. 46 * is expected.
47 * @x: 64bit integer of which to calculate the 47 * @x: 64bit integer of which to calculate the sqrt
48 */ 48 */
49 u32 int_sqrt64(u64 x) 49 u32 int_sqrt64(u64 x)
50 { 50 {
51 u64 b, m, y = 0; 51 u64 b, m, y = 0;
52 52
53 if (x <= ULONG_MAX) 53 if (x <= ULONG_MAX)
54 return int_sqrt((unsigned long 54 return int_sqrt((unsigned long) x);
55 55
56 m = 1ULL << ((fls64(x) - 1) & ~1ULL); 56 m = 1ULL << ((fls64(x) - 1) & ~1ULL);
57 while (m != 0) { 57 while (m != 0) {
58 b = y + m; 58 b = y + m;
59 y >>= 1; 59 y >>= 1;
60 60
61 if (x >= b) { 61 if (x >= b) {
62 x -= b; 62 x -= b;
63 y += m; 63 y += m;
64 } 64 }
65 m >>= 2; 65 m >>= 2;
66 } 66 }
67 67
68 return y; 68 return y;
69 } 69 }
70 EXPORT_SYMBOL(int_sqrt64); 70 EXPORT_SYMBOL(int_sqrt64);
71 #endif 71 #endif
72 72
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