byte concat

#include <stdio.h>
#include <stdint.h>
const int len = 8;

uint64_t concat(uint8_t n[]) {
  uint64_t r = 0;
  for (int i = 0; i < len; i++) {
    r |= 1ULL * n[i] << (8ULL * i);
  }
  return r;
}

void showBits(uint64_t x, int msb) {
  for (int i = msb; i >= 0; i--) {
    printf("%llu", (x >> i) & 1);
    if (i % 4 == 0) {
      putchar(' ');
    }
  }
}

int main() {
  uint8_t n[len];
  for (int i = 0; i < len; i++) {
    printf("n%d=", i); scanf("%hhd", &n[i]);
  }
  for (int i = len - 1; i >= 0; i--) {
    showBits(n[i], sizeof(n[i]) * 8 - 1);
  }
  puts("");
  uint64_t r = concat(n);
  showBits(r, sizeof(r) * 8 - 1);
  puts("");
  return 0;
}