77 lines
2.2 KiB
C
77 lines
2.2 KiB
C
/* This is a small program used in order to understand the collision rate
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* of CRC64 (ISO version) VS other stronger hashing functions in the context
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* of hashing keys for the Redis "tracking" feature (client side caching
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* assisted by the server).
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*
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* The program attempts to hash keys with common names in the form of
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*
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* prefix:<counter>
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*
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* And counts the resulting collisions generated in the 24 bits of output
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* needed for the tracking feature invalidation table (16 millions + entries)
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*
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* Compile with:
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*
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* cc -O2 ./tracking_collisions.c ../src/crc64.c ../src/sha1.c
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* ./a.out
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*
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* --------------------------------------------------------------------------
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*
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* Copyright (C) 2019 Salvatore Sanfilippo
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* This code is released under the BSD 2 clause license.
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*/
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#include <stdlib.h>
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#include <stdint.h>
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#include <string.h>
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#include <stdio.h>
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#include "../src/crc64.h"
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#include "../src/sha1.h"
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#define TABLE_SIZE (1<<24)
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int Table[TABLE_SIZE];
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uint64_t crc64Hash(char *key, size_t len) {
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return crc64(0,(unsigned char*)key,len);
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}
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uint64_t sha1Hash(char *key, size_t len) {
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SHA1_CTX ctx;
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unsigned char hash[20];
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SHA1Init(&ctx);
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SHA1Update(&ctx,(unsigned char*)key,len);
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SHA1Final(hash,&ctx);
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uint64_t hash64;
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memcpy(&hash64,hash,sizeof(hash64));
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return hash64;
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}
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/* Test the hashing function provided as callback and return the
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* number of collisions found. */
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unsigned long testHashingFunction(uint64_t (*hash)(char *, size_t)) {
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unsigned long collisions = 0;
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memset(Table,0,sizeof(Table));
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char *prefixes[] = {"object", "message", "user", NULL};
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for (int i = 0; prefixes[i] != NULL; i++) {
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for (int j = 0; j < TABLE_SIZE/2; j++) {
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char keyname[128];
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size_t keylen = snprintf(keyname,sizeof(keyname),"%s:%d",
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prefixes[i],j);
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uint64_t bucket = hash(keyname,keylen) % TABLE_SIZE;
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if (Table[bucket]) {
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collisions++;
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} else {
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Table[bucket] = 1;
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}
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}
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}
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return collisions;
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}
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int main(void) {
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printf("SHA1 : %lu\n", testHashingFunction(sha1Hash));
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printf("CRC64: %lu\n", testHashingFunction(crc64Hash));
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return 0;
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}
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