/*
This file contains source code to implement a dictionary using
skip lists and a test driver to test the routines.
A couple of comments about this implementation:
The routine randomLevel has been hard-coded to generate random
levels using p=0.25. It can be easily changed.
The insertion routine has been implemented so as to use the
dirty hack described in the CACM paper: if a random level is
generated that is more than the current maximum level, the
current maximum level plus one is used instead.
Levels start at zero and go up to MaxLevel (which is equal to
(MaxNumberOfLevels-1).
The compile flag allowDuplicates determines whether or not duplicates
are allowed. If defined, duplicates are allowed and act in a FIFO manner.
If not defined, an insertion of a value already in the file updates the
previously existing binding.
BitsInRandom is defined to be the number of bits returned by a call to
random(). For most all machines with 32-bit integers, this is 31 bits
as currently set.
The routines defined in this file are:
init: defines NIL and initializes the random bit source
newList: returns a new, empty list
freeList(l): deallocates the list l (along with any elements in l)
randomLevel: Returns a random level
insert(l,key,value): inserts the binding (key,value) into l. If
allowDuplicates is undefined, returns true if key was newly
inserted into the list, false if key already existed
delete(l,key): deletes any binding of key from the l. Returns
false if key was not defined.
search(l,key,&value): Searches for key in l and returns true if found.
If found, the value associated with key is stored in the
location pointed to by &value
*/
#define false 0
#define true 1
typedef char boolean;
#define BitsInRandom 31
#define allowDuplicates
#define MaxNumberOfLevels 16
#define MaxLevel (MaxNumberOfLevels-1)
#define newNodeOfLevel(l) (node)malloc(sizeof(struct nodeStructure)+(l)*sizeof(node *))
typedef int keyType;
typedef int valueType;
#ifdef allowDuplicates
boolean delete(), search();
void insert();
#else
boolean insert(), delete(), search();
#endif
typedef struct nodeStructure *node;
typedef struct nodeStructure{
keyType key;
valueType value;
node forward[1]; /* variable sized array of forward pointers */
};
typedef struct listStructure{
int level; /* Maximum level of the list
(1 more than the number of levels in the list) */
struct nodeStructure * header; /* pointer to header */
} * list;
node NIL;
int randomsLeft;
int randomBits;
init() {
NIL = newNodeOfLevel(0);
NIL->key = 0x7fffffff;
randomBits = random();
randomsLeft = BitsInRandom/2;
};
list newList() {
list l;
int i;
l = (list)malloc(sizeof(struct listStructure));
l->level = 0;
l->header = newNodeOfLevel(MaxNumberOfLevels);
for(i=0;iheader->forward[i] = NIL;
return(l);
};
freeList(l)
list l;
{
register node p,q;
p = l->header;
do {
q = p->forward[0];
free(p);
p = q; }
while (p!=NIL);
free(l);
};
int randomLevel()
{register int level = 0;
register int b;
do {
b = randomBits&3;
if (!b) level++;
randomBits>>=2;
if (--randomsLeft == 0) {
randomBits = random();
randomsLeft = BitsInRandom/2;
};
} while (!b);
return(level>MaxLevel ? MaxLevel : level);
};
#ifdef allowDuplicates
void insert(l,key,value)
#else
boolean insert(l,key,value)
#endif
register list l;
register keyType key;
register valueType value;
{
register int k;
node update[MaxNumberOfLevels];
register node p,q;
p = l->header;
k = l->level;
do {
while (q = p->forward[k], q->key < key) p = q;
update[k] = p;
} while(--k>=0);
#ifndef allowDuplicates
if (q->key == key) {
q->value = value;
return(false);
};
#endif
k = randomLevel();
if (k>l->level) {
k = ++l->level;
update[k] = l->header;
};
q = newNodeOfLevel(k);
q->key = key;
q->value = value;
do {
p = update[k];
q->forward[k] = p->forward[k];
p->forward[k] = q;
} while(--k>=0);
#ifndef allowDuplicates
return(true);
#endif
}
boolean delete(l,key)
register list l;
register keyType key;
{
register int k,m;
node update[MaxNumberOfLevels];
register node p,q;
p = l->header;
k = m = l->level;
do {
while (q = p->forward[k], q->key < key) p = q;
update[k] = p;
} while(--k>=0);
if (q->key == key) {
for(k=0; k<=m && (p=update[k])->forward[k] == q; k++)
p->forward[k] = q->forward[k];
free(q);
while( l->header->forward[m] == NIL && m > 0 )
m--;
l->level = m;
return(true);
}
else return(false);
}
boolean search(l,key,valuePointer)
register list l;
register keyType key;
valueType * valuePointer;
{
register int k;
register node p,q;
p = l->header;
k = l->level;
do while (q = p->forward[k], q->key < key) p = q;
while (--k>=0);
if (q->key != key) return(false);
*valuePointer = q->value;
return(true);
};
#define sampleSize 65536
main() {
list l;
register int i,k;
keyType keys[sampleSize];
valueType v;
init();
l= newList();
for(k=0;k
Search