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use different (better) hashing algorithm

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ceriel 1989-06-19 11:17:41 +00:00
parent a9102764e6
commit 1205b95090
1 changed files with 7 additions and 37 deletions
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44
modules/src/idf/idf_pkg.body
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@ -2,29 +2,11 @@
#include <alloc.h> #include <alloc.h>
/* Each character of the identifier is xored with an 8-bit mask which #define IDF_HASHSIZE 307 /* size of hashtable, must be odd */
depends on the position of the character; the sum of these results
is the hash value. The random masks are obtained from a
congruence generator.
*/
#define IDF_HASHSIZE 256 /* size of hashtable, must be a power of 2 */
#ifndef IDF_HSIZE
#define IDF_HSIZE 16 /* # of significant characters for hashing.
This is NOT the number of significant
characters!
*/
#endif
#define IDF_HASH_X 0253 /* Knuth's X */
#define IDF_HASH_A 77 /* Knuth's a */
#define IDF_HASH_C 153 /* Knuth's c */
#define IDF_HASHMASK (IDF_HASHSIZE-1) /* since it is a power of 2 */
#define IDF_STARTHASH(hs) (hs = 0) #define IDF_STARTHASH(hs) (hs = 0)
#define IDF_ENHASH(hs,ch,hm) (hs += (ch ^ hm)) #define IDF_ENHASH(hs,ch) (hs = (hs << 2) + ch)
#define IDF_STOPHASH(hs) (hs &= IDF_HASHMASK) #define IDF_STOPHASH(hs) (hs = hs % IDF_HASHSIZE)
static char IDF_hmask[IDF_HSIZE];
static struct idf *IDF_hashtable[IDF_HASHSIZE]; static struct idf *IDF_hashtable[IDF_HASHSIZE];
/* All identifiers can in principle be reached through /* All identifiers can in principle be reached through
@ -100,19 +82,17 @@ str2idf(tg, cpy)
identifier tg. If necessary, an entry is created. identifier tg. If necessary, an entry is created.
*/ */
register char *cp = tg; register char *cp = tg;
register char *phm = &IDF_hmask[0];
struct idf **hook; struct idf **hook;
register struct idf *notch; register struct idf *notch;
register int hash; register unsigned int hash;
int size; int size;
IDF_STARTHASH(hash); IDF_STARTHASH(hash);
while (*cp && phm < &IDF_hmask[IDF_HSIZE]) { while (*cp) {
IDF_ENHASH(hash, *cp++, *phm++); IDF_ENHASH(hash, *cp++);
} }
IDF_STOPHASH(hash); IDF_STOPHASH(hash);
while (*cp++) /* nothing. Find end of string */ ; size = cp - tg + 1;
size = cp - tg;
/* The tag tg with length size and known hash value hash is /* The tag tg with length size and known hash value hash is
looked up in the identifier table; if not found, it is looked up in the identifier table; if not found, it is
@ -146,14 +126,4 @@ str2idf(tg, cpy)
} }
init_idf() { init_idf() {
/* A simple congruence random number generator, as
described in Knuth, vol 2.
*/
register int rnd = IDF_HASH_X;
register char *phm;
for (phm = &IDF_hmask[0]; phm < &IDF_hmask[IDF_HSIZE];) {
*phm++ = rnd;
rnd = (IDF_HASH_A * rnd + IDF_HASH_C) & IDF_HASHMASK;
}
} }