Hash.c 8.24 KB
Newer Older
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314
/*-----------------------------------------------------------------------------
 * $Id: Hash.c,v 1.1 1999/01/27 12:11:25 simonm Exp $
 *
 * (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 "Rts.h"
#include "Hash.h"
#include "RtsUtils.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 */
struct hashlist {
    StgWord key;
    void *data;
    struct hashlist *next;  /* Next cell in bucket chain (same hash value) */
};

typedef struct hashlist HashList;

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 */
};

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

static int
hash(HashTable *table, W_ 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;
}

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

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

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

/* -----------------------------------------------------------------------------
 * 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 *freeList = NULL;

static HashList *
allocHashList(void)
{
    HashList *hl, *p;

    if ((hl = freeList) != NULL) {
	freeList = hl->next;
    } else {
        hl = stgMallocBytes(HCHUNK * sizeof(HashList), "allocHashList");

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

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

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

    /* We want no duplicates */
    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 = hash(table, key);
    segment = bucket / HSEGSIZE;
    index = bucket % HSEGSIZE;

    hl = allocHashList();

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

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

    /* 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);
		freeHashList(hl);
	    }
	    index--;
	}
	free(table->dir[segment]);
	segment--;
	index = HSEGSIZE - 1;
    }
    free(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(void)
{
    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;

    return table;
}