d0894409d1
The CPU_NO_EFFICIENT_FFS pre-processor macro is no longer used, with all architectures toggling the equivalent Kconfig symbol CONFIG_CPU_NO_EFFICIENT_FFS instead. Remove our check for the unused macro. Signed-off-by: Paul Burton <paul.burton@mips.com> Patchwork: https://patchwork.linux-mips.org/patch/21046/ Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Zhaoxiu Zeng <zhaoxiu.zeng@gmail.com> Cc: linux-mips@linux-mips.org Cc: linux-kernel@vger.kernel.org
84 lines
1.4 KiB
C
84 lines
1.4 KiB
C
#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)
|
|
|
|
/* If __ffs is available, the even/odd algorithm benchmarks slower. */
|
|
|
|
/**
|
|
* 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;
|
|
|
|
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);
|