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Home Page: http://www.isthe.com/chongo/tech/comp/fnv/index.html
#=====================# # Fowler/Noll/Vo hash # #=====================# The basis of this hash algorithm was taken from an idea sent as reviewer comments to the IEEE POSIX P1003.2 committee by: Phong Vo (http://www.research.att.com/info/kpv) Glenn Fowler (http://www.research.att.com/~gsf/) In a subsequent ballot round: Landon Curt Noll (http://www.isthe.com/chongo) improved on their algorithm. Some people tried this hash and found that it worked rather well. In an EMail message to Landon, they named it the ``Fowler/Noll/Vo'' or FNV hash. FNV hashes are designed to be fast while maintaining a low collision rate. The FNV speed allows one to quickly hash lots of data while maintaining a reasonable collision rate. See: http://www.isthe.com/chongo/tech/comp/fnv/index.html for more details as well as other forms of the FNV hash. Comments, questions, bug fixes and suggestions welcome at the address given in the above URL. #==================# # FNV hash utility # #==================# Two hash utilities (32 bit and 64 bit) are provided: fnv032 [-b bcnt] [-m] [-s arg] [-t code] [-v] [arg ...] fnv132 [-b bcnt] [-m] [-s arg] [-t code] [-v] [arg ...] fnv1a32 [-b bcnt] [-m] [-s arg] [-t code] [-v] [arg ...] fnv064 [-b bcnt] [-m] [-s arg] [-t code] [-v] [arg ...] fnv164 [-b bcnt] [-m] [-s arg] [-t code] [-v] [arg ...] fnv1a64 [-b bcnt] [-m] [-s arg] [-t code] [-v] [arg ...] -b bcnt mask off all but the lower bcnt bits (default: 32) -m multiple hashes, one per line for each arg -s hash arg as a string (ignoring terminating NUL bytes) -t code 0 ==> generate test vectors, 1 ==> test FNV hash -v verbose mode, print arg after hash (implies -m) arg string (if -s was given) or filename (default stdin) The fnv032, fnv064 implement the historic FNV-0 hash. The fnv132, fnv164 implement the recommended FNV-1 hash. The fnv1a32, fnv1a64 implement the recommended FNV-1a hash. This is the original historic FNV algorithm with a 0 offset basis. It is recommended that FNV-1, with a non-0 offset basis be used instead. To test FNV hashes, try: fnv032 -t 1 -v fnv132 -t 1 -v fnv1a32 -t 1 -v fnv064 -t 1 -v fnv164 -t 1 -v fnv1a64 -t 1 -v If you are compiling, try: make check #==================# # FNV hash library # #==================# The libfnv.a library implements both a 32 bit and a 64 bit FNV hash on collections of bytes, a NUL terminated strings or on an open file descriptor. Here is the 32 bit FNV 1 hash: Fnv32_t fnv_32_buf(void *buf, int len, Fnv32_t hval); /* byte buf */ Fnv32_t fnv_32_str(char *string, Fnv32_t hval); /* string */ Here is the 32 bit FNV 1a hash: Fnv32_t fnv_32a_buf(void *buf, int len, Fnv32_t hval); /* byte buf */ Fnv32_t fnv_32a_str(char *string, Fnv32_t hval); /* string */ Here is the 64 bit FNV 1 hash: Fnv64_t fnv_64_buf(void *buf, int len, Fnv64_t hval); /* byte buf */ Fnv64_t fnv_64_str(char *string, Fnv64_t hval); /* string */ Here is the 64 bit FNV 1a hash: Fnv64_t fnv_64a_buf(void *buf, int len, Fnv64_t hval); /* byte buf */ Fnv64_t fnv_64a_str(char *string, Fnv64_t hval); /* string */ On the first call to a hash function, one must supply the initial basis that is appropriate for the hash in question: FNV-0: (not recommended) FNV0_32_INIT /* 32 bit FNV-0 initial basis */ FNV0_64_INIT /* 64 bit FNV-0 initial basis */ FNV-1: FNV1_32_INIT /* 32 bit FNV-1 initial basis */ FNV1_64_INIT /* 64 bit FNV-1 initial basis */ FNV-1a: FNV1A_32_INIT /* 32 bit FNV-1a initial basis */ FNV1A_64_INIT /* 64 bit FNV-1a initial basis */ For example to perform a 64 bit FNV-1 hash: #include "fnv.h" Fnv64_t hash_val; hash_val = fnv_64_str("a string", FNV1_64_INIT); hash_val = fnv_64_str("more string", hash_val); produces the same final hash value as: hash_val = fnv_64_str("a stringmore string", FNV1_64_INIT); NOTE: If one used 'FNV0_64_INIT' instead of 'FNV1_64_INIT' one would get the historic FNV-0 hash instead recommended FNV-1 hash. To perform a 32 bit FNV-1 hash: #include "fnv.h" Fnv32_t hash_val; hash_val = fnv_32_buf(buf, length_of_buf, FNV1_32_INIT); hash_val = fnv_32_str("more data", hash_val); To perform a 64 bit FNV-1a hash: #include "fnv.h" Fnv64_t hash_val; hash_val = fnv_64a_buf(buf, length_of_buf, FNV1_64_INIT); hash_val = fnv_64a_str("more data", hash_val); =-= chongo <Landon Curt Noll> /\oo/\ http://www.isthe.com/chongo Share and Enjoy!
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