4d284daefd
Update references of copyright being assigned to Salvatore when it was transferred to Redis Ltd. as per https://github.com/valkey-io/valkey/issues/544. --------- Signed-off-by: Pieter Cailliau <pieter@redis.com>
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
|
|
* of CRC64 (ISO version) VS other stronger hashing functions in the context
|
|
* of hashing keys for the "tracking" feature (client side caching
|
|
* assisted by the server).
|
|
*
|
|
* The program attempts to hash keys with common names in the form of
|
|
*
|
|
* prefix:<counter>
|
|
*
|
|
* And counts the resulting collisions generated in the 24 bits of output
|
|
* needed for the tracking feature invalidation table (16 millions + entries)
|
|
*
|
|
* Compile with:
|
|
*
|
|
* cc -O2 ./tracking_collisions.c ../src/crc64.c ../src/sha1.c
|
|
* ./a.out
|
|
*
|
|
* --------------------------------------------------------------------------
|
|
*
|
|
* Copyright (C) 2019 Redis Ltd.
|
|
* This code is released under the BSD 2 clause license.
|
|
*/
|
|
|
|
#include <stdlib.h>
|
|
#include <stdint.h>
|
|
#include <string.h>
|
|
#include <stdio.h>
|
|
#include "../src/crc64.h"
|
|
#include "../src/sha1.h"
|
|
|
|
#define TABLE_SIZE (1<<24)
|
|
int Table[TABLE_SIZE];
|
|
|
|
uint64_t crc64Hash(char *key, size_t len) {
|
|
return crc64(0,(unsigned char*)key,len);
|
|
}
|
|
|
|
uint64_t sha1Hash(char *key, size_t len) {
|
|
SHA1_CTX ctx;
|
|
unsigned char hash[20];
|
|
|
|
SHA1Init(&ctx);
|
|
SHA1Update(&ctx,(unsigned char*)key,len);
|
|
SHA1Final(hash,&ctx);
|
|
uint64_t hash64;
|
|
memcpy(&hash64,hash,sizeof(hash64));
|
|
return hash64;
|
|
}
|
|
|
|
/* Test the hashing function provided as callback and return the
|
|
* number of collisions found. */
|
|
unsigned long testHashingFunction(uint64_t (*hash)(char *, size_t)) {
|
|
unsigned long collisions = 0;
|
|
memset(Table,0,sizeof(Table));
|
|
char *prefixes[] = {"object", "message", "user", NULL};
|
|
for (int i = 0; prefixes[i] != NULL; i++) {
|
|
for (int j = 0; j < TABLE_SIZE/2; j++) {
|
|
char keyname[128];
|
|
size_t keylen = snprintf(keyname,sizeof(keyname),"%s:%d",
|
|
prefixes[i],j);
|
|
uint64_t bucket = hash(keyname,keylen) % TABLE_SIZE;
|
|
if (Table[bucket]) {
|
|
collisions++;
|
|
} else {
|
|
Table[bucket] = 1;
|
|
}
|
|
}
|
|
}
|
|
return collisions;
|
|
}
|
|
|
|
int main(void) {
|
|
printf("SHA1 : %lu\n", testHashingFunction(sha1Hash));
|
|
printf("CRC64: %lu\n", testHashingFunction(crc64Hash));
|
|
return 0;
|
|
}
|