#=====================#
# 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
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