/*
This is a short program to illustrate endianness. This performs a simple
memory trick that allows us to view the actual order of bytes in memory.

it then prints out what the program perceives as the byte order and the
actual order in memory.

To compile: gcc -o endian 08-endian.c
To run: ./endian


C. Andrews

2013-09-20
*/

#include <stdio.h>
#include <stdint.h>


int main(int argc, char * argv[]){

  // the union stores both of these items in the same location in memory
  // So, if I access this using .i, I can treat this memory as an int, and if
  // I use C, it is an array of characters.
  union {
    uint32_t i;
    char c[sizeof(uint32_t)];
  } u;

  // Set the value using the integer
  u.i = 0x12345678;


  // test the first byte in the array to see if it has the "high" byte
  if (u.c[0] == 0x12){
    printf("Big Endian\n");
  }else{
    printf("Little Endian\n");
  }


  // print out what the program sees
  // we are using bit twiddling to mask out and extract the actual bytes
  printf("Apparent storage: ");

  for (int i = 3; i >=0; i--){
    printf("%hhx ", (u.i >> (i * 8)) & 0xff);
  }
  printf( "\n");


  // print out how it is stored in memory
  // this just reads the data out of the array
  printf("Actual storage: ");
  for (int i = 0; i < 4; i++){
    printf("%hhx ", u.c[i]);
  }
  printf( "\n");



  return 0;
}