diff options
Diffstat (limited to 'lib/math/div64.c')
| -rw-r--r-- | lib/math/div64.c | 46 |
1 files changed, 45 insertions, 1 deletions
diff --git a/lib/math/div64.c b/lib/math/div64.c index 368ca7fd0d82..46866394fc84 100644 --- a/lib/math/div64.c +++ b/lib/math/div64.c @@ -18,9 +18,11 @@ * or by defining a preprocessor macro in arch/include/asm/div64.h. */ +#include <linux/bitops.h> #include <linux/export.h> -#include <linux/kernel.h> +#include <linux/math.h> #include <linux/math64.h> +#include <linux/log2.h> /* Not needed on 64bit architectures */ #if BITS_PER_LONG == 32 @@ -190,3 +192,45 @@ u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder) return __iter_div_u64_rem(dividend, divisor, remainder); } EXPORT_SYMBOL(iter_div_u64_rem); + +#ifndef mul_u64_u64_div_u64 +u64 mul_u64_u64_div_u64(u64 a, u64 b, u64 c) +{ + u64 res = 0, div, rem; + int shift; + + /* can a * b overflow ? */ + if (ilog2(a) + ilog2(b) > 62) { + /* + * (b * a) / c is equal to + * + * (b / c) * a + + * (b % c) * a / c + * + * if nothing overflows. Can the 1st multiplication + * overflow? Yes, but we do not care: this can only + * happen if the end result can't fit in u64 anyway. + * + * So the code below does + * + * res = (b / c) * a; + * b = b % c; + */ + div = div64_u64_rem(b, c, &rem); + res = div * a; + b = rem; + + shift = ilog2(a) + ilog2(b) - 62; + if (shift > 0) { + /* drop precision */ + b >>= shift; + c >>= shift; + if (!c) + return res; + } + } + + return res + div64_u64(a * b, c); +} +EXPORT_SYMBOL(mul_u64_u64_div_u64); +#endif |