Contributors: 7
| Author |
Tokens |
Token Proportion |
Commits |
Commit Proportion |
| Zeng Zhaoxiu |
170 |
58.42% |
1 |
14.29% |
| Florian Fainelli |
84 |
28.87% |
1 |
14.29% |
| Kuan-Wei Chiu |
27 |
9.28% |
1 |
14.29% |
| Davidlohr Bueso A |
7 |
2.41% |
1 |
14.29% |
| Thomas Gleixner |
1 |
0.34% |
1 |
14.29% |
| Paul Gortmaker |
1 |
0.34% |
1 |
14.29% |
| Randy Dunlap |
1 |
0.34% |
1 |
14.29% |
| Total |
291 |
|
7 |
|
// SPDX-License-Identifier: GPL-2.0-only
#include <linux/kernel.h>
#include <linux/gcd.h>
#include <linux/export.h>
/*
* This implements the binary GCD algorithm. (Often attributed to Stein,
* but as Knuth has noted, appears in a first-century Chinese math text.)
*
* This is faster than the division-based algorithm even on x86, which
* has decent hardware division.
*/
DEFINE_STATIC_KEY_TRUE(efficient_ffs_key);
#if !defined(CONFIG_CPU_NO_EFFICIENT_FFS)
/* If __ffs is available, the even/odd algorithm benchmarks slower. */
static unsigned long binary_gcd(unsigned long a, unsigned long b)
{
unsigned long r = a | b;
b >>= __ffs(b);
if (b == 1)
return r & -r;
for (;;) {
a >>= __ffs(a);
if (a == 1)
return r & -r;
if (a == b)
return a << __ffs(r);
if (a < b)
swap(a, b);
a -= b;
}
}
#endif
/* If normalization is done by loops, the even/odd algorithm is a win. */
/**
* gcd - calculate and return the greatest common divisor of 2 unsigned longs
* @a: first value
* @b: second value
*/
unsigned long gcd(unsigned long a, unsigned long b)
{
unsigned long r = a | b;
if (!a || !b)
return r;
#if !defined(CONFIG_CPU_NO_EFFICIENT_FFS)
if (static_branch_likely(&efficient_ffs_key))
return binary_gcd(a, b);
#endif
/* Isolate lsbit of r */
r &= -r;
while (!(b & r))
b >>= 1;
if (b == r)
return r;
for (;;) {
while (!(a & r))
a >>= 1;
if (a == r)
return r;
if (a == b)
return a;
if (a < b)
swap(a, b);
a -= b;
a >>= 1;
if (a & r)
a += b;
a >>= 1;
}
}
EXPORT_SYMBOL_GPL(gcd);