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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-11 08:27:49 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-11 08:27:49 +0000 |
commit | ace9429bb58fd418f0c81d4c2835699bddf6bde6 (patch) | |
tree | b2d64bc10158fdd5497876388cd68142ca374ed3 /lib/math/gcd.c | |
parent | Initial commit. (diff) | |
download | linux-ace9429bb58fd418f0c81d4c2835699bddf6bde6.tar.xz linux-ace9429bb58fd418f0c81d4c2835699bddf6bde6.zip |
Adding upstream version 6.6.15.upstream/6.6.15
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
-rw-r--r-- | lib/math/gcd.c | 85 |
1 files changed, 85 insertions, 0 deletions
diff --git a/lib/math/gcd.c b/lib/math/gcd.c new file mode 100644 index 0000000000..e3b042214d --- /dev/null +++ b/lib/math/gcd.c @@ -0,0 +1,85 @@ +// 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. + */ + +#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); |