On 11/16/2011 01:14 PM, MORITA Kazutaka wrote: > At Tue, 15 Nov 2011 11:16:43 +0800, > Liu Yuan wrote: >> >> From: Liu Yuan <tailai.ly at taobao.com> >> >> These are trivial helper wrappers around standard IO functions >> and interger hash function. "stolen" from git and Linux kernel. >> >> Signed-off-by: Liu Yuan <tailai.ly at taobao.com> >> --- >> include/util.h | 63 +++++++++++++++++++++++ >> sheep/util.c | 150 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ >> 2 files changed, 213 insertions(+), 0 deletions(-) >> create mode 100644 sheep/util.c >> >> diff --git a/include/util.h b/include/util.h >> index 2dccd16..c73a6d5 100644 >> --- a/include/util.h >> +++ b/include/util.h >> @@ -2,6 +2,8 @@ >> #define __UTIL_H__ >> >> #include <string.h> >> +#include <limits.h> >> +#include <stdint.h> >> >> #include "bitops.h" >> >> @@ -53,4 +55,65 @@ static inline void *zalloc(size_t size) >> return calloc(1, size); >> } >> >> +typedef void (*try_to_free_t)(size_t); >> +extern try_to_free_t set_try_to_free_routine(try_to_free_t); >> + >> +extern void *xmalloc(size_t size); >> +extern void *xzalloc(size_t size); >> +extern void *xrealloc(void *ptr, size_t size); >> +extern void *xcalloc(size_t nmemb, size_t size); >> +extern ssize_t xread(int fd, void *buf, size_t len); >> +extern ssize_t xwrite(int fd, const void *buf, size_t len); >> + >> +/* Integer hash functions, taken from Linux kernel. >> + * Use hash_long() to get most out of your cpu. >> + */ >> + >> +/* 2^31 + 2^29 - 2^25 + 2^22 - 2^19 - 2^16 + 1 */ >> +#define GOLDEN_RATIO_PRIME_32 0x9e370001UL >> +/* 2^63 + 2^61 - 2^57 + 2^54 - 2^51 - 2^18 + 1 */ >> +#define GOLDEN_RATIO_PRIME_64 0x9e37fffffffc0001UL >> + >> +#if __SIZEOF_POINTER__ == 4 >> +#define GOLDEN_RATIO_PRIME GOLDEN_RATIO_PRIME_32 >> +#define hash_long(val, bits) hash_32(val, bits) >> +#elif __SIZEOF_POINTER__ == 8 >> +#define hash_long(val, bits) hash_64(val, bits) >> +#define GOLDEN_RATIO_PRIME GOLDEN_RATIO_PRIME_64 >> +#else >> +#error Wordsize not 32 or 64 >> +#endif >> + >> +static inline uint64_t hash_64(uint64_t val, unsigned int bits) >> +{ >> + uint64_t hash = val; >> + >> + /* Sigh, gcc can't optimise this alone like it does for 32 bits. */ >> + uint64_t n = hash; >> + n <<= 18; >> + hash -= n; >> + n <<= 33; >> + hash -= n; >> + n <<= 3; >> + hash += n; >> + n <<= 3; >> + hash -= n; >> + n <<= 4; >> + hash += n; >> + n <<= 2; >> + hash += n; >> + >> + /* High bits are more random, so use them. */ >> + return hash >> (64 - bits); >> +} >> + >> +static inline uint32_t hash_32(uint32_t val, unsigned int bits) >> +{ >> + /* On some cpus multiply is faster, on others gcc will do shifts */ >> + uint32_t hash = val * GOLDEN_RATIO_PRIME_32; >> + >> + /* High bits are more random, so use them. */ >> + return hash >> (32 - bits); >> +} > > We already have a hash function, fnv_64a_buf(). How about using it > instead of introducing new one? > When I need a hash function that inputs an integer and outputs an integer for specified bits, I looked at the fnv_64a_buf(), it seems to me it tries to hash an string to integer. So I think these hash functions do a different thing, no? Thanks, Yuan |