diff options
Diffstat (limited to 'kernel/include/linux/reciprocal_div.h')
-rw-r--r-- | kernel/include/linux/reciprocal_div.h | 35 |
1 files changed, 35 insertions, 0 deletions
diff --git a/kernel/include/linux/reciprocal_div.h b/kernel/include/linux/reciprocal_div.h new file mode 100644 index 000000000..8c5a3fb6c --- /dev/null +++ b/kernel/include/linux/reciprocal_div.h @@ -0,0 +1,35 @@ +#ifndef _LINUX_RECIPROCAL_DIV_H +#define _LINUX_RECIPROCAL_DIV_H + +#include <linux/types.h> + +/* + * This algorithm is based on the paper "Division by Invariant + * Integers Using Multiplication" by Torbjörn Granlund and Peter + * L. Montgomery. + * + * The assembler implementation from Agner Fog, which this code is + * based on, can be found here: + * http://www.agner.org/optimize/asmlib.zip + * + * This optimization for A/B is helpful if the divisor B is mostly + * runtime invariant. The reciprocal of B is calculated in the + * slow-path with reciprocal_value(). The fast-path can then just use + * a much faster multiplication operation with a variable dividend A + * to calculate the division A/B. + */ + +struct reciprocal_value { + u32 m; + u8 sh1, sh2; +}; + +struct reciprocal_value reciprocal_value(u32 d); + +static inline u32 reciprocal_divide(u32 a, struct reciprocal_value R) +{ + u32 t = (u32)(((u64)a * R.m) >> 32); + return (t + ((a - t) >> R.sh1)) >> R.sh2; +} + +#endif /* _LINUX_RECIPROCAL_DIV_H */ |