mirror of
http://git.haproxy.org/git/haproxy.git/
synced 2024-12-20 10:40:13 +00:00
3e31e2927c
We have a few places where we're checking many status codes. The sets are so small that just a multiply, a shift and an optional xor are sufficient to turn that into a smaller set. The program used to produce them is hackish as it allows to easily fiddle with various operations manually and experiment by brute-forcing a pair of integers for the mul and the xor. It also supports producing an incomplete table that gives an easier modulo operation. Let's commit it as-is so that it can be reused later (e.g. if new status codes are introduced for example).
114 lines
3.6 KiB
C
114 lines
3.6 KiB
C
/* Brute-force based perfect hash generator for small sets of integers. Just
|
|
* fill the table below with the integer values, try to pad a little bit to
|
|
* avoid too complicated divides, experiment with a few operations in the
|
|
* hash function and reuse the output as-is to make your table. You may also
|
|
* want to experiment with the random generator to use either one or two
|
|
* distinct values for mul and key.
|
|
*/
|
|
|
|
#include <stdio.h>
|
|
#include <stdlib.h>
|
|
|
|
/* warning no more than 32 distinct values! */
|
|
|
|
//#define CODES 21
|
|
//#define CODES 20
|
|
//#define CODES 19
|
|
//const int codes[CODES] = { 200,400,401,403,404,405,407,408,410,413,421,422,425,429,500,501,502,503,504};
|
|
|
|
#define CODES 32
|
|
const int codes[CODES] = { 200,400,401,403,404,405,407,408,410,413,421,422,425,429,500,501,502,503,504,
|
|
/* padding entries below, which will fall back to the default code */
|
|
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1};
|
|
|
|
unsigned mul, xor;
|
|
unsigned bmul = 0, bxor = 0;
|
|
|
|
static unsigned rnd32seed = 0x11111111U;
|
|
static unsigned rnd32()
|
|
{
|
|
rnd32seed ^= rnd32seed << 13;
|
|
rnd32seed ^= rnd32seed >> 17;
|
|
rnd32seed ^= rnd32seed << 5;
|
|
return rnd32seed;
|
|
}
|
|
|
|
/* the hash function to use in the target code. Try various combinations of
|
|
* multiplies and xor, always folded with a modulo, and try to spot the
|
|
* simplest operations if possible. Sometimes it may be worth adding a few
|
|
* dummy codes to get a better modulo code. In this case, just add dummy
|
|
* values at the end, but always distinct from the original ones. If the
|
|
* number of codes is even, it might be needed to rotate left the result
|
|
* before the modulo to compensate for lost LSBs.
|
|
*/
|
|
unsigned hash(unsigned i)
|
|
{
|
|
//return ((i * mul) - (i ^ xor)) % CODES; // more solutions
|
|
//return ((i * mul) + (i ^ xor)) % CODES; // alternate
|
|
//return ((i ^ xor) * mul) % CODES; // less solutions but still OK for sequences up to 19 long
|
|
//return ((i * mul) ^ xor) % CODES; // less solutions but still OK for sequences up to 19 long
|
|
|
|
i = i * mul;
|
|
i >>= 5;
|
|
//i = i ^ xor;
|
|
//i = (i << 30) | (i >> 2); // rotate 2 right
|
|
//i = (i << 2) | (i >> 30); // rotate 2 left
|
|
//i |= i >> 20;
|
|
//i += i >> 30;
|
|
//i |= i >> 16;
|
|
return i % CODES;
|
|
//return ((i * mul) ^ xor) % CODES; // less solutions but still OK for sequences up to 19 long
|
|
}
|
|
|
|
int main(int argc, char **argv)
|
|
{
|
|
unsigned h, i, flag, best, tests;
|
|
|
|
if (argc > 2) {
|
|
mul = atol(argv[1]);
|
|
xor = atol(argv[2]);
|
|
for (i = 0; i < CODES && codes[i] >= 0; i++)
|
|
printf("hash(%4u) = %4u // [%4u] = %4u\n", codes[i], hash(codes[i]), hash(codes[i]), codes[i]);
|
|
return 0;
|
|
}
|
|
|
|
tests = 0;
|
|
best = 0;
|
|
while (/*best < CODES &&*/ ++tests) {
|
|
mul = rnd32();
|
|
xor = mul; // works for some sequences up to 21 long
|
|
//xor = rnd32(); // more solutions
|
|
|
|
flag = 0;
|
|
for (i = 0; i < CODES && codes[i] >= 0; i++) {
|
|
h = hash(codes[i]);
|
|
if (flag & (1 << h))
|
|
break;
|
|
flag |= 1 << h;
|
|
}
|
|
|
|
if (i > best ||
|
|
(i == best && mul <= bmul && xor <= bxor)) {
|
|
/* find the best code and try to find the smallest
|
|
* parameters among the best ones (need to disable
|
|
* best<CODES in the loop for this). Small values are
|
|
* interesting for some multipliers, and for some RISC
|
|
* architectures where literals can be loaded in less
|
|
* instructions.
|
|
*/
|
|
best = i;
|
|
bmul = mul;
|
|
bxor = xor;
|
|
printf("%u: mul=%u xor=%u\n", best, bmul, bxor);
|
|
}
|
|
|
|
if ((tests & 0x7ffff) == 0)
|
|
printf("%u tests...\r", tests);
|
|
}
|
|
printf("%u tests, %u vals with mul=%u xor=%u:\n", tests, best, bmul, bxor);
|
|
|
|
mul = bmul; xor = bxor;
|
|
for (i = 0; i < CODES && codes[i] >= 0; i++)
|
|
printf("hash(%4u) = %2u // [%2u] = %4u\n", codes[i], hash(codes[i]), hash(codes[i]), codes[i]);
|
|
}
|