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| #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.
| */
|
| #if !defined(CONFIG_CPU_NO_EFFICIENT_FFS) && !defined(CPU_NO_EFFICIENT_FFS)
|
| /* If __ffs is available, the even/odd algorithm benchmarks slower. */
| unsigned long gcd(unsigned long a, unsigned long b)
| {
| unsigned long r = a | b;
|
| if (!a || !b)
| return r;
|
| 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;
| }
| }
|
| #else
|
| /* If normalization is done by loops, the even/odd algorithm is a win. */
| unsigned long gcd(unsigned long a, unsigned long b)
| {
| unsigned long r = a | b;
|
| if (!a || !b)
| return r;
|
| /* 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;
| }
| }
|
| #endif
|
| EXPORT_SYMBOL_GPL(gcd);
|
|
