diff options
Diffstat (limited to '')
| -rw-r--r-- | tests/exp/ip-hash.c | 202 |
1 files changed, 202 insertions, 0 deletions
diff --git a/tests/exp/ip-hash.c b/tests/exp/ip-hash.c new file mode 100644 index 0000000..8bb2d48 --- /dev/null +++ b/tests/exp/ip-hash.c @@ -0,0 +1,202 @@ +/* + * 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; +} |