Get special numbers from a random number generator
- by Wikeno
I have a random number generator:
int32_t ksp_random_table[GENERATOR_DEG] = {
-1726662223, 379960547, 1735697613, 1040273694, 1313901226, 1627687941,
-179304937, -2073333483, 1780058412, -1989503057, -615974602, 344556628,
939512070, -1249116260, 1507946756, -812545463, 154635395, 1388815473,
-1926676823, 525320961, -1009028674, 968117788, -123449607, 1284210865,
435012392, -2017506339, -911064859, -370259173, 1132637927, 1398500161,
-205601318,
};
int front_pointer=3, rear_pointer=0;
int32_t ksp_rand() {
int32_t result;
ksp_random_table[ front_pointer ] += ksp_random_table[ rear_pointer ];
result = ( ksp_random_table[ front_pointer ] >> 1 ) & 0x7fffffff;
front_pointer++, rear_pointer++;
if (front_pointer >= GENERATOR_DEG) front_pointer = 0;
if (rear_pointer >= GENERATOR_DEG) rear_pointer = 0;
return result;
}
void ksp_srand(unsigned int seed) {
int32_t i, dst=0, kc=GENERATOR_DEG, word, hi, lo;
word = ksp_random_table[0] = (seed==0) ? 1 : seed;
for (i = 1; i < kc; ++i) {
hi = word / 127773, lo = word % 127773;
word = 16807 * lo - 2836 * hi;
if (word < 0) word += 2147483647;
ksp_random_table[++dst] = word;
}
front_pointer=3, rear_pointer=0;
kc *= 10;
while (--kc >= 0) ksp_rand();
}
I'd like know what type of pseudo random number generation algorithm this is. My guess is a multiple linear congruential generator. And is there a way of seeding this algorithm so that after 987721(1043*947) numbers it would return 15 either even-only, odd-only or alternating odd and even numbers? It is a part of an assignment for a long term competition and i've got no idea how to solve it.
I don't want the final solution, I'd like to learn how to do it myself.
