haproxy/tests/ip-hash.c

203 lines
5.6 KiB
C

/*
* Integer hashing tests. These functions work with 32-bit integers, so are
* perfectly suited for IPv4 addresses. A few tests show that they may also
* be chained for larger keys (eg: IPv6), this way :
* f(x[0-3]) = f(f(f(f(x[0])^x[1])^x[2])^x[3])
*
* See also bob jenkin's site for more info on hashing, and check perfect
* hashing for constants (eg: header names).
*/
#include <stdio.h>
#include <string.h>
#include <arpa/inet.h>
#include <math.h>
#define NSERV 8
#define MAXLINE 1000
int counts_id[NSERV][NSERV];
uint32_t hash_id( uint32_t a)
{
return a;
}
/* Full-avalanche integer hashing function from Thomas Wang, suitable for use
* with a modulo. See below, worth a read !
* http://www.concentric.net/~Ttwang/tech/inthash.htm
*
* See also tests performed by Bob Jenkins (says it's faster than his) :
* http://burtleburtle.net/bob/hash/integer.html
*
* This function is small and fast. It does not seem as smooth as bj6 though.
* About 0x40 bytes, 6 shifts.
*/
int counts_tw1[NSERV][NSERV];
uint32_t hash_tw1(uint32_t a)
{
a += ~(a<<15);
a ^= (a>>10);
a += (a<<3);
a ^= (a>>6);
a += ~(a<<11);
a ^= (a>>16);
return a;
}
/* Thomas Wang's mix function. The multiply is optimized away by the compiler
* on most platforms.
* It is about equivalent to the one above.
*/
int counts_tw2[NSERV][NSERV];
uint32_t hash_tw2(uint32_t a)
{
a = ~a + (a << 15);
a = a ^ (a >> 12);
a = a + (a << 2);
a = a ^ (a >> 4);
a = a * 2057;
a = a ^ (a >> 16);
return a;
}
/* Thomas Wang's multiplicative hash function. About 0x30 bytes, and it is
* extremely fast on recent processors with a fast multiply. However, it
* must not be used on low bits only, as multiples of 0x00100010 only return
* even values !
*/
int counts_tw3[NSERV][NSERV];
uint32_t hash_tw3(uint32_t a)
{
a = (a ^ 61) ^ (a >> 16);
a = a + (a << 3);
a = a ^ (a >> 4);
a = a * 0x27d4eb2d;
a = a ^ (a >> 15);
return a;
}
/* Full-avalanche integer hashing function from Bob Jenkins, suitable for use
* with a modulo. It has a very smooth distribution.
* http://burtleburtle.net/bob/hash/integer.html
* About 0x50 bytes, 6 shifts.
*/
int counts_bj6[NSERV][NSERV];
int counts_bj6x[NSERV][NSERV];
uint32_t hash_bj6(uint32_t a)
{
a = (a+0x7ed55d16) + (a<<12);
a = (a^0xc761c23c) ^ (a>>19);
a = (a+0x165667b1) + (a<<5);
a = (a+0xd3a2646c) ^ (a<<9);
a = (a+0xfd7046c5) + (a<<3);
a = (a^0xb55a4f09) ^ (a>>16);
return a;
}
/* Similar function with one more shift and no magic number. It is slightly
* slower but provides the overall smoothest distribution.
* About 0x40 bytes, 7 shifts.
*/
int counts_bj7[NSERV][NSERV];
int counts_bj7x[NSERV][NSERV];
uint32_t hash_bj7(uint32_t a)
{
a -= (a<<6);
a ^= (a>>17);
a -= (a<<9);
a ^= (a<<4);
a -= (a<<3);
a ^= (a<<10);
a ^= (a>>15);
return a;
}
void count_hash_results(unsigned long hash, int counts[NSERV][NSERV]) {
int srv, nsrv;
for (nsrv = 0; nsrv < NSERV; nsrv++) {
srv = hash % (nsrv + 1);
counts[nsrv][srv]++;
}
}
void dump_hash_results(char *name, int counts[NSERV][NSERV]) {
int srv, nsrv;
double err, total_err, max_err;
printf("%s:\n", name);
for (nsrv = 0; nsrv < NSERV; nsrv++) {
total_err = 0.0;
max_err = 0.0;
printf("%02d srv: ", nsrv+1);
for (srv = 0; srv <= nsrv; srv++) {
err = 100.0*(counts[nsrv][srv] - (double)counts[0][0]/(nsrv+1)) / (double)counts[0][0];
//printf("%6d ", counts[nsrv][srv]);
printf("% 3.1f%%%c ", err,
counts[nsrv][srv]?' ':'*'); /* display '*' when a server is never selected */
err = fabs(err);
total_err += err;
if (err > max_err)
max_err = err;
}
total_err /= (double)(nsrv+1);
for (srv = nsrv+1; srv < NSERV; srv++)
printf(" ");
printf(" avg_err=%3.1f, max_err=%3.1f\n", total_err, max_err);
}
printf("\n");
}
int main() {
int nr;
unsigned int address = 0;
unsigned int mask = ~0;
memset(counts_id, 0, sizeof(counts_id));
memset(counts_tw1, 0, sizeof(counts_tw1));
memset(counts_tw2, 0, sizeof(counts_tw2));
memset(counts_tw3, 0, sizeof(counts_tw3));
memset(counts_bj6, 0, sizeof(counts_bj6));
memset(counts_bj7, 0, sizeof(counts_bj7));
address = 0x10000000;
mask = 0xffffff00; // user mask to apply to addresses
for (nr = 0; nr < 0x10; nr++) {
//address += ~nr; // semi-random addresses.
//address += 1;
address += 0x00000100;
//address += 0x11111111;
//address += 7;
//address += 8;
//address += 256;
//address += 65536;
//address += 131072;
//address += 0x00100010; // this increment kills tw3 !
count_hash_results(hash_id (address & mask), counts_id); // 0.69s / 100M
count_hash_results(hash_tw1(address & mask), counts_tw1); // 1.04s / 100M
count_hash_results(hash_tw2(address & mask), counts_tw2); // 1.13s / 100M
count_hash_results(hash_tw3(address & mask), counts_tw3); // 1.01s / 100M
count_hash_results(hash_bj6(address & mask), counts_bj6); // 1.07s / 100M
count_hash_results(hash_bj7(address & mask), counts_bj7); // 1.20s / 100M
/* adding the original address after the hash reduces the error
* rate in in presence of very small data sets (eg: 16 source
* addresses for 8 servers). In this case, bj7 is very good.
*/
count_hash_results(hash_bj6(address & mask)+(address&mask), counts_bj6x); // 1.07s / 100M
count_hash_results(hash_bj7(address & mask)+(address&mask), counts_bj7x); // 1.20s / 100M
}
dump_hash_results("hash_id", counts_id);
dump_hash_results("hash_tw1", counts_tw1);
dump_hash_results("hash_tw2", counts_tw2);
dump_hash_results("hash_tw3", counts_tw3);
dump_hash_results("hash_bj6", counts_bj6);
dump_hash_results("hash_bj6x", counts_bj6x);
dump_hash_results("hash_bj7", counts_bj7);
dump_hash_results("hash_bj7x", counts_bj7x);
return 0;
}