duperemove/bloom.h at master · mknjc/duperemove · GitHub

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/*
 *  Copyright (c) 2012, Jyri J. Virkki
 *  All rights reserved.
 *
 *  This file is under BSD license. See LICENSE file.
 */

#ifndef _BLOOM_H
#define _BLOOM_H

#include <stdint.h>

/** ***************************************************************************
 * Structure to keep track of one bloom filter.  Caller needs to
 * allocate this and pass it to the functions below. First call for
 * every struct must be to bloom_init().
 *
 */
struct bloom {
	/*
	 * These fields are part of the public interface of this structure.
	 * Client code may read these values if desired. Client code MUST NOT
	 * modify any of these.
	 */
	int entries;
	double error;
	uint64_t bits;
	uint64_t bytes;
	int hashes;

	/* Fields below are private to the implementation. These may go away or
	 * change incompatibly at any moment. Client code MUST NOT access or
	 * rely on these.
	 */
	double bpe;
	unsigned char *bf;
	int ready;
};


/** ***************************************************************************
 * Initialize the bloom filter for use.
 *
 * The filter is initialized with a bit field and number of hash functions
 * according to the computations from the wikipedia entry:
 *     http://en.wikipedia.org/wiki/Bloom_filter
 *
 * Optimal number of bits is:
 *     bits = (entries * ln(error)) / ln(2)^2
 *
 * Optimal number of hash functions is:
 *     hashes = bpe * ln(2)
 *
 * Parameters:
 * -----------
 *     bloom   - Pointer to an allocated struct bloom (see above).
 *     entries - The expected number of entries which will be inserted.
 *     error   - Probability of collision (as long as entries are not
 *               exceeded).
 *
 * Return:
 * -------
 *     0 - on success
 *     1 - on failure
 *
 */
int bloom_init(struct bloom *bloom, int entries, double error);


/** ***************************************************************************
 * Check if the given element is in the bloom filter. Remember this may
 * return false positive if a collision occured.
 *
 * Parameters:
 * -----------
 *     bloom  - Pointer to an allocated struct bloom (see above).
 *     buffer - Pointer to buffer containing element to check.
 *     len    - Size of 'buffer'.
 *
 * Return:
 * -------
 *     0 - element is not present
 *     1 - element is present (or false positive due to collision)
 *    -1 - bloom not initialized
 *
 */
int bloom_check(struct bloom *bloom, void *buffer, int len);


/** ***************************************************************************
 * Add the given element to the bloom filter.
 * The return code indicates if the element (or a collision) was already in,
 * so for the common check+add use case, no need to call check separately.
 *
 * Parameters:
 * -----------
 *     bloom  - Pointer to an allocated struct bloom (see above).
 *     buffer - Pointer to buffer containing element to add.
 *     len    - Size of 'buffer'.
 *
 * Return:
 * -------
 *     0 - element was not present and was added
 *     1 - element (or a collision) had already been added previously
 *    -1 - bloom not initialized
 *
 */
int bloom_add(struct bloom *bloom, void *buffer, int len);


/** ***************************************************************************
 * Print (to stdout) info about this bloom filter. Debugging aid.
 *
 */
void bloom_print(struct bloom *bloom);


/** ***************************************************************************
 * Deallocate internal storage.
 *
 * Upon return, the bloom struct is no longer usable. You may call bloom_init
 * again on the same struct to reinitialize it again.
 *
 * Parameters:
 * -----------
 *     bloom  - Pointer to an allocated struct bloom (see above).
 *
 * Return: none
 *
 */
void bloom_free(struct bloom *bloom);

#endif