This repository is based on the FNV reference source published by Landon Curt Noll with modifications to make it easier to include in my own projects.
The basis of this hash algorithm was taken from an idea sent as reviewer comments to the IEEE POSIX P1003.2 committee by:
In a subsequent ballot round:
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 here 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.
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
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 /\oo/
http://www.isthe.com/chongo
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