cpp/stutterfuzz
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Fix random algo to evenly distribute.

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This commit is contained in:
Ian Gulliver
2016-03-04 10:17:10 -08:00
parent 213cad5417
commit d9d5db9efe
1 changed files with 6 additions and 18 deletions
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24
stutterfuzz.c
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@@ -3,32 +3,20 @@
#include "rand.h" #include "rand.h"
static uint64_t sqrt64(uint64_t n) { static uint64_t get_split(uint64_t total_len, uint64_t remaining_len) {
uint64_t g = UINT64_C(1) << 31;
for (uint64_t c = g; c; g |= c) {
if (g * g > n) {
g ^= c;
}
c >>= 1;
}
return g;
}
static uint64_t get_split(uint64_t len) {
uint64_t rnd; uint64_t rnd;
rand_fill(&rnd, sizeof(rnd)); rand_fill(&rnd, sizeof(rnd));
rnd %= (len * len); rnd %= total_len;
return sqrt64(rnd) + 1; return rnd > remaining_len ? remaining_len : rnd;
} }
int main(int __attribute__ ((unused)) argc, char __attribute__ ((unused)) *argv[]) { int main(int __attribute__ ((unused)) argc, char __attribute__ ((unused)) *argv[]) {
rand_init(); rand_init();
for (uint64_t len = 1397; len;) { uint64_t total_len = 1397;
uint64_t consume = get_split(len); for (uint64_t remaining = total_len, consume = 0; remaining; remaining -= consume) {
consume = get_split(total_len, remaining);
fprintf(stderr, "consume %ju bytes\n", (uintmax_t) consume); fprintf(stderr, "consume %ju bytes\n", (uintmax_t) consume);
len -= consume;
} }
rand_cleanup(); rand_cleanup();