mirror of
https://github.com/Kaehvaman/OAIP.git
synced 2025-01-31 09:28:24 +04:00
87 lines
2.3 KiB
C
87 lines
2.3 KiB
C
#pragma once
|
||
|
||
/*
|
||
* https://en.wikipedia.org/wiki/Fowler–Noll–Vo_hash_function
|
||
* http://www.isthe.com/chongo/tech/comp/fnv/index.html
|
||
*/
|
||
|
||
/*
|
||
* To use the recommended 32 bit FNV-1a hash, pass FNV1_32A_INIT as the
|
||
* Fnv32_t hashval argument to fnv_32a_buf() or fnv_32a_str().
|
||
*/
|
||
|
||
typedef uint32_t Fnv32_t;
|
||
|
||
/*
|
||
* 32 bit magic FNV-1a prime
|
||
*/
|
||
#define FNV_32_PRIME ((Fnv32_t)0x01000193)
|
||
|
||
/*
|
||
* 32 bit FNV-1 and FNV-1a non-zero initial basis
|
||
*
|
||
* The FNV-1 initial basis is the FNV-0 hash of the following 32 octets:
|
||
*
|
||
* chongo <Landon Curt Noll> /\../\
|
||
*
|
||
* NOTE: The \'s above are not back-slashing escape characters.
|
||
* They are literal ASCII backslash 0x5c characters.
|
||
*
|
||
* NOTE: The FNV-1a initial basis is the same value as FNV-1 by definition.
|
||
*/
|
||
#define FNV1_32_INIT ((Fnv32_t)0x811c9dc5)
|
||
#define FNV1_32A_INIT FNV1_32_INIT
|
||
|
||
/*
|
||
* If you need an x-bit hash where x is not a power of 2,
|
||
* then we recommend that you compute the FNV hash that is just larger than x-bits
|
||
* and xor-fold the result down to x-bits.By xor-folding we mean shift the excess
|
||
* high order bits down and xor them with the lower x - bits.
|
||
*/
|
||
|
||
//For example to produce a 24 bit FNV-1 hash in C we xor-fold fold a 32 bit FNV-1 hash:
|
||
|
||
#define MASK_24 (((uint32_t)1<<24)-1) /* i.e., (uint32_t)0xffffff */
|
||
/*
|
||
uint32_t hash;
|
||
void* data;
|
||
size_t data_len;
|
||
|
||
hash = fnv_32_buf(data, data_len, FNV1_32_INIT);
|
||
hash = (hash >> 24) ^ (hash & MASK_24);
|
||
*/
|
||
|
||
#define FNV_24(hash) ((hash >> 24) ^ (hash & MASK_24))
|
||
|
||
//To produce a 16 bit FNV-1 hash in C we xor-fold fold a 32 bit FNV-1 hash:
|
||
|
||
#define MASK_16 (((uint32_t)1<<16)-1) /* i.e., (uint32_t)0xffff */
|
||
/*
|
||
uint32_t hash;
|
||
void* data;
|
||
size_t data_len;
|
||
|
||
hash = fnv_32_buf(data, data_len, FNV1_32_INIT);
|
||
hash = (hash >> 16) ^ (hash & MASK_16);
|
||
*/
|
||
|
||
#define FNV_16(hash) ((hash >> 16) ^ (hash & MASK_16))
|
||
|
||
//For tiny x < 16 bit values, we recommend using a 32 bit FNV - 1 hash as follows:
|
||
|
||
/* NOTE: for 0 < x < 16 ONLY!!! */
|
||
#define TINY_MASK(x) (((uint32_t)1<<(x))-1)
|
||
/*
|
||
uint32_t hash;
|
||
void* data;
|
||
size_t data_len;
|
||
|
||
hash = fnv_32_buf(data, data_len, FNV1_32_INIT);
|
||
hash = (((hash >> x) ^ hash) & TINY_MASK(x));
|
||
*/
|
||
|
||
#define TINY_FNV(x, hash) (((hash >> x) ^ hash) & TINY_MASK(x))
|
||
|
||
Fnv32_t fnv_32a_buf(void* buf, size_t len, Fnv32_t hval);
|
||
Fnv32_t fnv_32a_str(char* str, Fnv32_t hval);
|