path: root/source/fitz/hash.c

#include "mupdf/fitz.h"

#include <string.h>
#include <assert.h>

/*
Simple hashtable with open addressing linear probe.
Unlike text book examples, removing entries works
correctly in this implementation, so it won't start
exhibiting bad behaviour if entries are inserted
and removed frequently.
*/

enum { MAX_KEY_LEN = 48 };
typedef struct fz_hash_entry_s fz_hash_entry;

struct fz_hash_entry_s
{
	unsigned char key[MAX_KEY_LEN];
	void *val;
};

struct fz_hash_table_s
{
	int keylen;
	int size;
	int load;
	int lock; /* -1 or the lock used to protect this hash table */
	fz_hash_table_drop_fn *drop_val;
	fz_hash_entry *ents;
};

static unsigned hash(const unsigned char *s, int len)
{
	unsigned val = 0;
	int i;
	for (i = 0; i < len; i++)
	{
		val += s[i];
		val += (val << 10);
		val ^= (val >> 6);
	}
	val += (val << 3);
	val ^= (val >> 11);
	val += (val << 15);
	return val;
}

fz_hash_table *
fz_new_hash_table(fz_context *ctx, int initialsize, int keylen, int lock, fz_hash_table_drop_fn *drop_val)
{
	fz_hash_table *table;

	assert(keylen <= MAX_KEY_LEN);

	table = fz_malloc_struct(ctx, fz_hash_table);
	table->keylen = keylen;
	table->size = initialsize;
	table->load = 0;
	table->lock = lock;
	table->drop_val = drop_val;
	fz_try(ctx)
	{
		table->ents = fz_malloc_array(ctx, table->size, sizeof(fz_hash_entry));
		memset(table->ents, 0, sizeof(fz_hash_entry) * table->size);
	}
	fz_catch(ctx)
	{
		fz_free(ctx, table);
		fz_rethrow(ctx);
	}

	return table;
}

void
fz_drop_hash_table(fz_context *ctx, fz_hash_table *table)
{
	if (!table)
		return;

	if (table->drop_val)
	{
		int i, n = table->size;
		for (i = 0; i < n; ++i)
		{
			void *v = table->ents[i].val;
			if (v)
				table->drop_val(ctx, v);
		}
	}

	fz_free(ctx, table->ents);
	fz_free(ctx, table);
}

static void *
do_hash_insert(fz_context *ctx, fz_hash_table *table, const void *key, void *val)
{
	fz_hash_entry *ents;
	unsigned size;
	unsigned pos;

	ents = table->ents;
	size = table->size;
	pos = hash(key, table->keylen) % size;

	if (table->lock >= 0)
		fz_assert_lock_held(ctx, table->lock);

	while (1)
	{
		if (!ents[pos].val)
		{
			memcpy(ents[pos].key, key, table->keylen);
			ents[pos].val = val;
			table->load ++;
			return NULL;
		}

		if (memcmp(key, ents[pos].key, table->keylen) == 0)
		{
			/* This is legal, but should rarely happen. */
			fz_warn(ctx, "assert: overwrite hash slot");
			return ents[pos].val;
		}

		pos = (pos + 1) % size;
	}
}

/* Entered with the lock taken, held throughout and at exit, UNLESS the lock
 * is the alloc lock in which case it may be momentarily dropped. */
static void
fz_resize_hash(fz_context *ctx, fz_hash_table *table, int newsize)
{
	fz_hash_entry *oldents = table->ents;
	fz_hash_entry *newents;
	int oldsize = table->size;
	int oldload = table->load;
	int i;

	if (newsize < oldload * 8 / 10)
	{
		fz_warn(ctx, "assert: resize hash too small");
		return;
	}

	if (table->lock == FZ_LOCK_ALLOC)
		fz_unlock(ctx, table->lock);
	newents = fz_malloc_array_no_throw(ctx, newsize, sizeof(fz_hash_entry));
	if (table->lock == FZ_LOCK_ALLOC)
		fz_lock(ctx, table->lock);
	if (table->lock >= 0)
	{
		if (table->size >= newsize)
		{
			/* Someone else fixed it before we could lock! */
			if (table->lock == FZ_LOCK_ALLOC)
				fz_unlock(ctx, table->lock);
			fz_free(ctx, newents);
			if (table->lock == FZ_LOCK_ALLOC)
				fz_lock(ctx, table->lock);
			return;
		}
	}
	if (newents == NULL)
		fz_throw(ctx, FZ_ERROR_GENERIC, "hash table resize failed; out of memory (%d entries)", newsize);
	table->ents = newents;
	memset(table->ents, 0, sizeof(fz_hash_entry) * newsize);
	table->size = newsize;
	table->load = 0;

	for (i = 0; i < oldsize; i++)
	{
		if (oldents[i].val)
		{
			do_hash_insert(ctx, table, oldents[i].key, oldents[i].val);
		}
	}

	if (table->lock == FZ_LOCK_ALLOC)
		fz_unlock(ctx, table->lock);
	fz_free(ctx, oldents);
	if (table->lock == FZ_LOCK_ALLOC)
		fz_lock(ctx, table->lock);
}

void *
fz_hash_find(fz_context *ctx, fz_hash_table *table, const void *key)
{
	fz_hash_entry *ents = table->ents;
	unsigned size = table->size;
	unsigned pos = hash(key, table->keylen) % size;

	if (table->lock >= 0)
		fz_assert_lock_held(ctx, table->lock);

	while (1)
	{
		if (!ents[pos].val)
			return NULL;

		if (memcmp(key, ents[pos].key, table->keylen) == 0)
			return ents[pos].val;

		pos = (pos + 1) % size;
	}
}

void *
fz_hash_insert(fz_context *ctx, fz_hash_table *table, const void *key, void *val)
{
	if (table->load > table->size * 8 / 10)
		fz_resize_hash(ctx, table, table->size * 2);
	return do_hash_insert(ctx, table, key, val);
}

static void
do_removal(fz_context *ctx, fz_hash_table *table, const void *key, unsigned hole)
{
	fz_hash_entry *ents = table->ents;
	unsigned size = table->size;
	unsigned look, code;

	if (table->lock >= 0)
		fz_assert_lock_held(ctx, table->lock);

	ents[hole].val = NULL;

	look = hole + 1;
	if (look == size)
		look = 0;

	while (ents[look].val)
	{
		code = hash(ents[look].key, table->keylen) % size;
		if ((code <= hole && hole < look) ||
			(look < code && code <= hole) ||
			(hole < look && look < code))
		{
			ents[hole] = ents[look];
			ents[look].val = NULL;
			hole = look;
		}

		look++;
		if (look == size)
			look = 0;
	}

	table->load --;
}

void
fz_hash_remove(fz_context *ctx, fz_hash_table *table, const void *key)
{
	fz_hash_entry *ents = table->ents;
	unsigned size = table->size;
	unsigned pos = hash(key, table->keylen) % size;

	if (table->lock >= 0)
		fz_assert_lock_held(ctx, table->lock);

	while (1)
	{
		if (!ents[pos].val)
		{
			fz_warn(ctx, "assert: remove non-existent hash entry");
			return;
		}

		if (memcmp(key, ents[pos].key, table->keylen) == 0)
		{
			do_removal(ctx, table, key, pos);
			return;
		}

		pos++;
		if (pos == size)
			pos = 0;
	}
}

void
fz_hash_for_each(fz_context *ctx, fz_hash_table *table, void *state, fz_hash_table_for_each_fn *callback)
{
	int i;
	for (i = 0; i < table->size; ++i)
		if (table->ents[i].val)
			callback(ctx, state, table->ents[i].key, table->keylen, table->ents[i].val);
}