path: root/rts/Hash.c

/*-----------------------------------------------------------------------------
 *
 * (c) The AQUA Project, Glasgow University, 1995-1998
 * (c) The GHC Team, 1999
 *
 * Dynamically expanding linear hash tables, as described in
 * Per-\AAke Larson, ``Dynamic Hash Tables,'' CACM 31(4), April 1988,
 * pp. 446 -- 457.
 * -------------------------------------------------------------------------- */

#include "PosixSource.h"
#include "Rts.h"

#include "Hash.h"
#include "RtsUtils.h"

#include <string.h>

#define HSEGSIZE    1024    /* Size of a single hash table segment */
                            /* Also the minimum size of a hash table */
#define HDIRSIZE    1024    /* Size of the segment directory */
                            /* Maximum hash table size is HSEGSIZE * HDIRSIZE */
#define HLOAD       5       /* Maximum average load of a single hash bucket */

#define HCHUNK      (1024 * sizeof(W_) / sizeof(HashList))
                            /* Number of HashList cells to allocate in one go */


/* Linked list of (key, data) pairs for separate chaining */
typedef struct hashlist {
    StgWord key;
    void *data;
    struct hashlist *next;  /* Next cell in bucket chain (same hash value) */
} HashList;

typedef struct chunklist {
  HashList *chunk;
  struct chunklist *next;
} HashListChunk;

struct hashtable {
    int split;              /* Next bucket to split when expanding */
    int max;                /* Max bucket of smaller table */
    int mask1;              /* Mask for doing the mod of h_1 (smaller table) */
    int mask2;              /* Mask for doing the mod of h_2 (larger table) */
    int kcount;             /* Number of keys */
    int bcount;             /* Number of buckets */
    HashList **dir[HDIRSIZE];   /* Directory of segments */
    HashList *freeList;         /* free list of HashLists */
    HashListChunk *chunks;
    HashFunction *hash;         /* hash function */
    CompareFunction *compare;   /* key comparison function */
};

/* -----------------------------------------------------------------------------
 * Hash first using the smaller table.  If the bucket is less than the
 * next bucket to be split, re-hash using the larger table.
 * -------------------------------------------------------------------------- */

int
hashWord(HashTable *table, StgWord key)
{
    int bucket;

    /* Strip the boring zero bits */
    key /= sizeof(StgWord);

    /* Mod the size of the hash table (a power of 2) */
    bucket = key & table->mask1;

    if (bucket < table->split) {
        /* Mod the size of the expanded hash table (also a power of 2) */
        bucket = key & table->mask2;
    }
    return bucket;
}

int
hashStr(HashTable *table, char *key)
{
    int h, bucket;
    char *s;

    s = key;
    for (h=0; *s; s++) {
        h *= 128;
        h += *s;
        h = h % 1048583;        /* some random large prime */
    }

    /* Mod the size of the hash table (a power of 2) */
    bucket = h & table->mask1;

    if (bucket < table->split) {
        /* Mod the size of the expanded hash table (also a power of 2) */
        bucket = h & table->mask2;
    }

    return bucket;
}

static int
compareWord(StgWord key1, StgWord key2)
{
    return (key1 == key2);
}

static int
compareStr(StgWord key1, StgWord key2)
{
    return (strcmp((char *)key1, (char *)key2) == 0);
}


/* -----------------------------------------------------------------------------
 * Allocate a new segment of the dynamically growing hash table.
 * -------------------------------------------------------------------------- */

static void
allocSegment(HashTable *table, int segment)
{
    table->dir[segment] = stgMallocBytes(HSEGSIZE * sizeof(HashList *),
                                         "allocSegment");
}


/* -----------------------------------------------------------------------------
 * Expand the larger hash table by one bucket, and split one bucket
 * from the smaller table into two parts.  Only the bucket referenced
 * by @table->split@ is affected by the expansion.
 * -------------------------------------------------------------------------- */

static void
expand(HashTable *table)
{
    int oldsegment;
    int oldindex;
    int newbucket;
    int newsegment;
    int newindex;
    HashList *hl;
    HashList *next;
    HashList *old, *new;

    if (table->split + table->max >= HDIRSIZE * HSEGSIZE)
        /* Wow!  That's big.  Too big, so don't expand. */
        return;

    /* Calculate indices of bucket to split */
    oldsegment = table->split / HSEGSIZE;
    oldindex = table->split % HSEGSIZE;

    newbucket = table->max + table->split;

    /* And the indices of the new bucket */
    newsegment = newbucket / HSEGSIZE;
    newindex = newbucket % HSEGSIZE;

    if (newindex == 0)
        allocSegment(table, newsegment);

    if (++table->split == table->max) {
        table->split = 0;
        table->max *= 2;
        table->mask1 = table->mask2;
        table->mask2 = table->mask2 << 1 | 1;
    }
    table->bcount++;

    /* Split the bucket, paying no attention to the original order */

    old = new = NULL;
    for (hl = table->dir[oldsegment][oldindex]; hl != NULL; hl = next) {
        next = hl->next;
        if (table->hash(table, hl->key) == newbucket) {
            hl->next = new;
            new = hl;
        } else {
            hl->next = old;
            old = hl;
        }
    }
    table->dir[oldsegment][oldindex] = old;
    table->dir[newsegment][newindex] = new;

    return;
}

void *
lookupHashTable(HashTable *table, StgWord key)
{
    int bucket;
    int segment;
    int index;
    HashList *hl;

    bucket = table->hash(table, key);
    segment = bucket / HSEGSIZE;
    index = bucket % HSEGSIZE;

    for (hl = table->dir[segment][index]; hl != NULL; hl = hl->next)
        if (table->compare(hl->key, key))
            return hl->data;

    /* It's not there */
    return NULL;
}

// Puts up to szKeys keys of the hash table into the given array. Returns the
// actual amount of keys that have been retrieved.
//
// If the table is modified concurrently, the function behavior is undefined.
//
int keysHashTable(HashTable *table, StgWord keys[], int szKeys) {
    int segment;
    int k = 0;
    for(segment=0;segment<HDIRSIZE && table->dir[segment];segment+=1) {
        int index;
        for(index=0;index<HSEGSIZE;index+=1) {
            HashList *hl;
            for(hl=table->dir[segment][index];hl;hl=hl->next) {
                if (k == szKeys)
                  return k;
                keys[k] = hl->key;
                k += 1;
            }
        }
    }
    return k;
}

/* -----------------------------------------------------------------------------
 * We allocate the hashlist cells in large chunks to cut down on malloc
 * overhead.  Although we keep a free list of hashlist cells, we make
 * no effort to actually return the space to the malloc arena.
 * -------------------------------------------------------------------------- */

static HashList *
allocHashList (HashTable *table)
{
    HashList *hl, *p;
    HashListChunk *cl;

    if ((hl = table->freeList) != NULL) {
        table->freeList = hl->next;
    } else {
        hl = stgMallocBytes(HCHUNK * sizeof(HashList), "allocHashList");
        cl = stgMallocBytes(sizeof (*cl), "allocHashList: chunkList");
        cl->chunk = hl;
        cl->next = table->chunks;
        table->chunks = cl;

        table->freeList = hl + 1;
        for (p = table->freeList; p < hl + HCHUNK - 1; p++)
            p->next = p + 1;
        p->next = NULL;
    }
    return hl;
}

static void
freeHashList (HashTable *table, HashList *hl)
{
    hl->next = table->freeList;
    table->freeList = hl;
}

void
insertHashTable(HashTable *table, StgWord key, void *data)
{
    int bucket;
    int segment;
    int index;
    HashList *hl;

    // Disable this assert; sometimes it's useful to be able to
    // overwrite entries in the hash table.
    // ASSERT(lookupHashTable(table, key) == NULL);

    /* When the average load gets too high, we expand the table */
    if (++table->kcount >= HLOAD * table->bcount)
        expand(table);

    bucket = table->hash(table, key);
    segment = bucket / HSEGSIZE;
    index = bucket % HSEGSIZE;

    hl = allocHashList(table);

    hl->key = key;
    hl->data = data;
    hl->next = table->dir[segment][index];
    table->dir[segment][index] = hl;

}

void *
removeHashTable(HashTable *table, StgWord key, void *data)
{
    int bucket;
    int segment;
    int index;
    HashList *hl;
    HashList *prev = NULL;

    bucket = table->hash(table, key);
    segment = bucket / HSEGSIZE;
    index = bucket % HSEGSIZE;

    for (hl = table->dir[segment][index]; hl != NULL; hl = hl->next) {
        if (table->compare(hl->key,key) && (data == NULL || hl->data == data)) {
            if (prev == NULL)
                table->dir[segment][index] = hl->next;
            else
                prev->next = hl->next;
            freeHashList(table,hl);
            table->kcount--;
            return hl->data;
        }
        prev = hl;
    }

    /* It's not there */
    ASSERT(data == NULL);
    return NULL;
}

/* -----------------------------------------------------------------------------
 * When we free a hash table, we are also good enough to free the
 * data part of each (key, data) pair, as long as our caller can tell
 * us how to do it.
 * -------------------------------------------------------------------------- */

void
freeHashTable(HashTable *table, void (*freeDataFun)(void *) )
{
    long segment;
    long index;
    HashList *hl;
    HashList *next;
    HashListChunk *cl, *cl_next;

    /* The last bucket with something in it is table->max + table->split - 1 */
    segment = (table->max + table->split - 1) / HSEGSIZE;
    index = (table->max + table->split - 1) % HSEGSIZE;

    while (segment >= 0) {
        while (index >= 0) {
            for (hl = table->dir[segment][index]; hl != NULL; hl = next) {
                next = hl->next;
                if (freeDataFun != NULL)
                    (*freeDataFun)(hl->data);
            }
            index--;
        }
        stgFree(table->dir[segment]);
        segment--;
        index = HSEGSIZE - 1;
    }
    for (cl = table->chunks; cl != NULL; cl = cl_next) {
        cl_next = cl->next;
        stgFree(cl->chunk);
        stgFree(cl);
    }
    stgFree(table);
}

/* -----------------------------------------------------------------------------
 * When we initialize a hash table, we set up the first segment as well,
 * initializing all of the first segment's hash buckets to NULL.
 * -------------------------------------------------------------------------- */

HashTable *
allocHashTable_(HashFunction *hash, CompareFunction *compare)
{
    HashTable *table;
    HashList **hb;

    table = stgMallocBytes(sizeof(HashTable),"allocHashTable");

    allocSegment(table, 0);

    for (hb = table->dir[0]; hb < table->dir[0] + HSEGSIZE; hb++)
        *hb = NULL;

    table->split = 0;
    table->max = HSEGSIZE;
    table->mask1 = HSEGSIZE - 1;
    table->mask2 = 2 * HSEGSIZE - 1;
    table->kcount = 0;
    table->bcount = HSEGSIZE;
    table->freeList = NULL;
    table->chunks = NULL;
    table->hash = hash;
    table->compare = compare;

    return table;
}

HashTable *
allocHashTable(void)
{
    return allocHashTable_(hashWord, compareWord);
}

HashTable *
allocStrHashTable(void)
{
    return allocHashTable_((HashFunction *)hashStr,
                           (CompareFunction *)compareStr);
}

void
exitHashTable(void)
{
    /* nothing to do */
}

int keyCountHashTable (HashTable *table)
{
    return table->kcount;
}