FNV与FNV-1a Hash算法说明【转】

转自:http://blog.csdn.net/jiayanhui2877/article/details/12090575

The core of the FNV hash

The core of the FNV-1 hash algorithm is as follows:
hash = offset_basis

for each octet_of_data to be hashed

 hash = hash * FNV_prime

 hash = hash xor octet_of_data

return hash
The offset_basis andFNV_prime can be found in theparameters of the FNV-1/FNV-1a hash section below.

FNV-1a alternate algorithm

There is a minor variation of the FNV hash algorithm known asFNV-1a:
hash = offset_basis

for each octet_of_data to be hashed

 hash = hash xor octet_of_data

 hash = hash * FNV_prime

return hash
The only difference between the FNV-1a hash and the FNV-1 hashis the order of the xor and multiply.The FNV-1a hashuses the same FNV_prime and offset_basisas the FNV-1 hash of the same n-bit size.

Parameters of the FNV-1/FNV-1a hash

The FNV-1 hash parameters are as follows:

hash is an n bit unsigned integer,where
n is the bit length of hash.

The multiplication is performed modulo 2ⁿwhere
n is the bit length of hash.

The xor is performed on the low orderoctet (8 bits) of hash.

The FNV_prime is dependent on n, the size of the hash:

32 bit FNV_prime =2²⁴ + 2⁸ + 0x93 =
16777619

64 bit FNV_prime = 2⁴⁰ + 2⁸ + 0xb3 =
1099511628211

128 bit FNV_prime = 2⁸⁸ + 2⁸ + 0x3b =
309485009821345068724781371

256 bit FNV_prime = 2¹⁶⁸ + 2⁸ + 0x63 =
374144419156711147060143317175368453031918731002211

512 bit FNV_prime = 2³⁴⁴ + 2⁸ + 0x57 =
35835915874844867368919076489095108449946327955754392558399825615420669938882575 126094039892345713852759

1024 bit FNV_prime = 2⁶⁸⁰ + 2⁸ + 0x8d =
50164565101131186554345988110352789550307653454047907443030175238311120551081474 51509157692220295382716162651878526895249385292291816524375083746691371804094271 873160484737966720260389217684476157468082573

Part of the magic of FNV is the selection of the FNV_primefor a given sized unsigned integer.Some primes do hash better than other primes for a given integer size.

The offset_basis for FNV-1 is dependent on
n, the size of the hash:

32 bit offset_basis = 2166136261

64 bit offset_basis = 14695981039346656037

128 bit offset_basis = 144066263297769815596495629667062367629

256 bit offset_basis = 100029257958052580907070968620625704837092796014241193945225284501741471925557

512 bit offset_basis = 96593031294966694980094354007163104660904187456726378961083743294344626579945829 32197716438449813051892206539805784495328239340083876191928701583869517785

1024 bit offset_basis = 14197795064947621068722070641403218320880622795441933960878474914617582723252296 73230371772215086409652120235554936562817466910857181476047101507614802975596980 40773201576924585630032153049571501574036444603635505054127112859663616102678680 82893823963790439336411086884584107735010676915

NOTE: Older versions of this web page incorretly indicated that the 128 bitFNV_prime was 2¹⁶⁸ + 2⁸ + 0x59.This was not correct.While that satisfied all of the significant
FNV_prime properties,it was not the smallest 128 bit
FNV_prime.The 128 bit offset_basischanged from275519064689413815358837431229664493455to144066263297769815596495629667062367629was changed as a result of the 128 bit
FNV_prime correction.(Sorry about that!)

巴特西

FNV与FNV-1a Hash算法说明【转】

The core of the FNV hash

FNV-1a alternate algorithm

Parameters of the FNV-1/FNV-1a hash

最新文章

热门文章