$ tcc -run -
#include <inttypes.h>
#include <stdint.h>
#include <stdio.h>
int main(void) {
 printf("%" PRIx64 "\n", (uint64_t)(double)0x3243bcfe21ef4468ULL);
 return 0;
}
^D
3243bcfe21ef4400

##</code><code>##

$ perl -MMath::BigInt -E'say Math::BigInt->new("0x3243bcfe21ef4468")->as_hex'
0x3243bcfe21ef4468