91 lines
2.6 KiB
C
91 lines
2.6 KiB
C
#include <assert.h>
|
|
#include <errno.h>
|
|
#include <limits.h>
|
|
#include <stdint.h>
|
|
#include <stdio.h>
|
|
#include <stdlib.h>
|
|
#include <sys/random.h>
|
|
#include <time.h>
|
|
|
|
#define error(ret, s, ...) \
|
|
do { \
|
|
fprintf(stderr, (s)__VA_OPT__(, __VA_ARGS__)); \
|
|
exit(ret); \
|
|
} while (0)
|
|
|
|
typedef unsigned long long ull;
|
|
|
|
typedef struct dynrdat {
|
|
size_t cap;
|
|
ull dat[];
|
|
} dynrdat;
|
|
|
|
static inline ull pow2_ceil(ull x) {
|
|
x -= !!x; // if x=0, remains 0; else x -= 1
|
|
int lz = __builtin_clzll(x | 1); // get leading zeroes
|
|
return (~0ULL >> lz) + 1; // bit-shift the maximum value by this amount of leading zeroes
|
|
}
|
|
|
|
int main(int argc, char** argv) {
|
|
// return the result if no input
|
|
if (argc <= 1) return printf("%s\n", (clock() & 1) ? "heads" : "tails");
|
|
|
|
dynrdat* rdat = NULL;
|
|
|
|
// loop through arguments
|
|
for (unsigned i = 1; i < (unsigned)argc; ++i) {
|
|
// parse the argument
|
|
errno = 0;
|
|
ull c = strtoull(argv[i], NULL, 10);
|
|
if (errno != 0) error(errno, "parse error for string: '%s'\n", argv[i]);
|
|
|
|
// acquire random data (compiler will optimize MOD and DIV away since they're both base-2 constant values)
|
|
int mod = c % (sizeof(ull) * 8); // get the remainder of the available random bits
|
|
c = c / (sizeof(ull) * 8); // compute our "word count"
|
|
|
|
// dynamically scale the array to our needs, ensuring 2^n scaling
|
|
size_t cap = pow2_ceil(c + !!mod);
|
|
if (!rdat || rdat->cap < cap) {
|
|
void* ptr = realloc(rdat, sizeof(dynrdat) + sizeof(ull) * cap);
|
|
if (!ptr) {
|
|
free(rdat);
|
|
error(1, "insufficient memory\n", );
|
|
}
|
|
|
|
rdat = ptr;
|
|
rdat->cap = cap;
|
|
}
|
|
|
|
// populate the array with random data
|
|
if (getrandom(rdat->dat, (c + !!mod) * sizeof(ull), 0) < 0)
|
|
error(1, "failed to acquire random data!\n", );
|
|
|
|
// perform for the input count
|
|
ull headsc = 0; // amount of heads
|
|
ull tailsc = 0; // amount of tails
|
|
|
|
// loop through how many full words there are available
|
|
ull* n = rdat->dat; // initialize the pointer to the start of our random data
|
|
for (; n < (rdat->dat + c); n++) {
|
|
int cnt = __builtin_popcountll(*n); // counts the set bits
|
|
headsc += cnt;
|
|
tailsc += sizeof(ull) * 8 - cnt;
|
|
}
|
|
|
|
// if there is a remainder, use the last N to get this
|
|
if (mod) {
|
|
ull msk = (1 << mod) - 1; // get a mask with the set word size
|
|
int cnt = __builtin_popcountll(*n & msk);
|
|
headsc += cnt;
|
|
tailsc += mod - cnt;
|
|
}
|
|
|
|
// print the results of this cycle
|
|
printf("results:\n heads: %llu\n tails: %llu\n", headsc, tailsc);
|
|
}
|
|
|
|
free(rdat);
|
|
|
|
return 0;
|
|
}
|