Bloom Filter 算法的实现

<<bloom.h>>=
#ifndef __BLOOM_H__
#define __BLOOM_H__

#include<stdlib.h>

typedef unsigned int (*hashfunc_t)(const char *);
typedef struct {
	size_t asize;
	unsigned char *a;
	size_t nfuncs;
	hashfunc_t *funcs;
} BLOOM;

BLOOM *bloom_create(size_t size, size_t nfuncs, ...);
int bloom_destroy(BLOOM *bloom);
int bloom_add(BLOOM *bloom, const char *s);
int bloom_check(BLOOM *bloom, const char *s);

#endif

<<bloom.c>>=
#include<limits.h>
#include<stdarg.h>

#include"bloom.h"

#define SETBIT(a, n) (a[n/CHAR_BIT] |= (1<<(n%CHAR_BIT)))
#define GETBIT(a, n) (a[n/CHAR_BIT] & (1<<(n%CHAR_BIT)))

BLOOM *bloom_create(size_t size, size_t nfuncs, ...)
{
	BLOOM *bloom;
	va_list l;
	int n;
	
	if(!(bloom=malloc(sizeof(BLOOM)))) return NULL;
	if(!(bloom->a=calloc((size+CHAR_BIT-1)/CHAR_BIT, sizeof(char)))) {
		free(bloom);
		return NULL;
	}
	if(!(bloom->funcs=(hashfunc_t*)malloc(nfuncs*sizeof(hashfunc_t)))) {
		free(bloom->a);
		free(bloom);
		return NULL;
	}

	va_start(l, nfuncs);
	for(n=0; n<nfuncs; ++n) {
		bloom->funcs[n]=va_arg(l, hashfunc_t);
	}
	va_end(l);

	bloom->nfuncs=nfuncs;
	bloom->asize=size;

	return bloom;
}

int bloom_destroy(BLOOM *bloom)
{
	free(bloom->a);
	free(bloom->funcs);
	free(bloom);

	return 0;
}

int bloom_add(BLOOM *bloom, const char *s)
{
	size_t n;

	for(n=0; n<bloom->nfuncs; ++n) {
		SETBIT(bloom->a, bloom->funcs[n](s)%bloom->asize);
	}

	return 0;
}

int bloom_check(BLOOM *bloom, const char *s)
{
	size_t n;

	for(n=0; n<bloom->nfuncs; ++n) {
		if(!(GETBIT(bloom->a, bloom->funcs[n](s)%bloom->asize))) return 0;
	}

	return 1;
}

<<test.c>>=

#include<stdio.h>
#include<string.h>

#include"bloom.h"

unsigned int sax_hash(const char *key)
{
	unsigned int h=0;

	while(*key) h^=(h<<5)+(h>>2)+(unsigned char)*key++;

	return h;
}

unsigned int sdbm_hash(const char *key)
{
	unsigned int h=0;
	while(*key) h=(unsigned char)*key++ + (h<<6) + (h<<16) - h;
	return h;
}

int main(int argc, char *argv[])
{
	FILE *fp;
	char line[1024];
	char *p;
	BLOOM *bloom;
	
	if(argc<2) {
		fprintf(stderr, "ERROR: No word file specified\n");
		return EXIT_FAILURE;
	}

	if(!(bloom=bloom_create(2500000, 2, sax_hash, sdbm_hash))) {
		fprintf(stderr, "ERROR: Could not create bloom filter\n");
		return EXIT_FAILURE;
	}

	if(!(fp=fopen(argv[1], "r"))) {
		fprintf(stderr, "ERROR: Could not open file %s\n", argv[1]);
		return EXIT_FAILURE;
	}

	while(fgets(line, 1024, fp)) {
		if((p=strchr(line, '\r'))) *p='\0';
		if((p=strchr(line, '\n'))) *p='\0';

		bloom_add(bloom, line);
	}

	fclose(fp);

	while(fgets(line, 1024, stdin)) {
		if((p=strchr(line, '\r'))) *p='\0';
		if((p=strchr(line, '\n'))) *p='\0';

		p=strtok(line, " \t,.;:\r\n?!-/()");
		while(p) {
			if(!bloom_check(bloom, p)) {
				printf("No match for ford \"%s\"\n", p);
			}
			p=strtok(NULL, " \t,.;:\r\n?!-/()");
		}
	}

	bloom_destroy(bloom);

	return EXIT_SUCCESS;
}

<<Makefile>>=
all: bloom

bloom: bloom.o test.o
	cc -o bloom -Wall -pedantic bloom.o test.o

bloom.o: bloom.c bloom.h
	cc -o bloom.o -Wall -pedantic -ansi -c bloom.c

test.o: test.c bloom.h
	cc -o test.o -Wall -pedantic -ansi -c test.c