[Sheepdog] [PATCH 2/5] sheep: add some candy helpers in util.c

[Liu Yuan]

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