uint64_t value creating from 8 bytes

[ard_newbie]

Maybe only 1 line should suffice (works on my DUE):

uint64_t bignum= 0x7165DB4B01000000; 
void setup() {
 
Serial.begin(250000);

}

void loop() {
bignum = __builtin_bswap64(bignum);
printf(" bignum = %lld\n", bignum);
while(1);
}