# Free Electrons

## Embedded Linux Experts

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78``` ```#include #include #include /* * 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); ```