bloom filter概念讲解以及代码分析

// 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"
//下面为两种哈希算法函数
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';//回车
if((p=strchr(line, '\n'))) *p='\0';//换行

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);
}
                    else
                      printf("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