drygdryg/calc
1
0
Fork 0
mirror of https://github.com/lcn2/calc.git synced 2025-08-16 01:03:29 +03:00
Code Issues Packages Projects Releases Wiki Activity

Release calc version 2.11.0t8.3

Browse Source
This commit is contained in:
Landon Curt Noll
1999-10-24 06:58:53 -07:00
parent a7d401cd65
commit 49be672338
8 changed files with 119 additions and 17 deletions
Download Patch File Download Diff File Expand all files Collapse all files

64
seed.c
View File

@@ -86,6 +86,50 @@ typedef struct s_hash64 hash64;
#endif
/*
* FNV-1 basis
*
* We start the hash at a non-zero value at the beginning so that
* hashing blocks of data with all 0 bits do not map onto the same
* 0 hash value. The virgin value that we use below is the hash value
* that we would get from following 32 ASCII characters:
*
* chongo <Landon Curt Noll> /\../\
*
* Note that the \'s above are not back-slashing escape characters.
* They are literal ASCII backslash 0x5c characters.
*
* The effect of this virgin initial value is the same as starting
* with 0 and pre-pending those 32 characters onto the data being
* hashed.
*
* Yes, even with this non-zero virgin value there is a set of data
* that will result in a zero hash value. Worse, appending any
* about of zero bytes will continue to produce a zero hash value.
* But that would happen with any initial value so long as the
* hash of the initial was the `inverse' of the virgin prefix string.
*
* But then again for any hash function, there exists sets of data
* which that the hash of every member is the same value. That is
* life with many to few mapping functions. All we do here is to
* prevent sets whose members consist of 0 or more bytes of 0's from
* being such an awkward set.
*
* And yes, someone can figure out what the magic 'inverse' of the
* 32 ASCII character are ... but this hash function is NOT intended
* to be a cryptographic hash function, just a fast and reasonably
* good hash function.
*/
#if defined(HAVE_B64)
# define FNV1_64_BASIS ((hash64)(0xcbf29ce484222325ULL))
#else
# define FNV1_64_BASIS_0 ((USB32)0x2325)
# define FNV1_64_BASIS_1 ((USB32)0x8422)
# define FNV1_64_BASIS_2 ((USB32)0x9ce4)
# define FNV1_64_BASIS_3 ((USB32)0xcbf2)
#endif
/*
* hash_buf - perform a 64 bit Fowler/Noll/Vo hash on a buffer
*
@@ -116,24 +160,16 @@ hash_buf(char *buf, unsigned len)
* (gsf@research.att.com).
*
* See:
* http://reality.sgi.com/chongo/src/fnv/fnv_hash.tar.gz
* http://reality.sgi.com/chongo/src/fnv/h32.c
* http://reality.sgi.com/chongo/src/fnv/h64.c
* http://reality.sgi.com/chongo/tech/comp/fnv/index.html
*
* for information on 32bit and 64bit Fowler/Noll/Vo hashes.
*
* Landon Curt Noll (http://reality.sgi.com/chongo) later improved
* on their algorithm to come up with Fowler/Noll/Vo hash.
*
* The 32 hash was able to process 234936 words from the web2 dictionary
* without any 32 bit collisions using a constant of
* 16777619 = 0x1000193.
*
* The 64 bit hash uses 1099511628211 = 0x100000001b3 instead.
*/
#if defined(HAVE_B64)
/* hash each octet of the buffer */
for (hval = (hash64)0ULL; buf < buf_end; ++buf) {
for (hval = FNV1_64_BASIS; buf < buf_end; ++buf) {
/* multiply by 1099511628211ULL mod 2^64 using 64 bit longs */
hval *= (hash64)1099511628211ULL;
@@ -145,7 +181,11 @@ hash_buf(char *buf, unsigned len)
#else /* HAVE_B64 */
/* hash each octet of the buffer */
for (val[0]=val[1]=val[2]=val[3]=0; buf < buf_end; ++buf) {
val[0] = FNV1_64_BASIS_0;
val[1] = FNV1_64_BASIS_1;
val[2] = FNV1_64_BASIS_2;
val[3] = FNV1_64_BASIS_3;
for (; buf < buf_end; ++buf) {
/*
* multiply by 1099511628211 mod 2^64 using 32 bit longs
@@ -167,7 +207,7 @@ hash_buf(char *buf, unsigned len)
val[0] = tmp[0] & 0xffff;
tmp[2] += (tmp[1] >> 16);
val[1] = tmp[1] & 0xffff;
val[3] += (tmp[2] >> 16);
val[3] = tmp[3] + (tmp[2] >> 16);
val[2] = tmp[2] & 0xffff;
/*
* Doing a val[3] &= 0xffff; is not really needed since it simply