Bits, endianess, and stack growing

Here some little bit oriented tricks.

• How to discover if your server is little endian or big endian?

bool endianess(){
int test_num = 1;
char *ptr = (char *) &test_num;          // this will return a byte
return (*ptr)
}

• How to count the number of bits set to 1 in the internal representation of a number?

int num_ones_in_binary_representation(int num){
 int num_ones = 0;
 while (num){
 if (num & 1)
    num_ones++;
 num = num >> 1;
 }
 return num_ones;
}

A more elegant solution:

int num_ones_in_binary_representation(int num){
 int num_ones = 0;
 while (num){
  num = num & (num - 1);  // consider the binary representation of num - 1 and subtract them
  num_ones++
 }
}

• Is your stack growing up or down?

Call two functions and take the address of their arguments, or consider the address of two consecutive variables within a function.