What is the difference between big and little endian floats?

Question

For integer values, it is pretty straightforward the difference in little endian and big endian representation.

But it is not clear for me how a little endian float differs from a big endian float.

And finally, I would like to know which is more commonly used.

Answer 1

Endianness just is a property of the bytes that make up a value that's composed from multiple bytes. Since a floating point number takes up 4 or 8 bytes endianness tells you in which order to read them. This is exactly the same as with integer values.

Answer 2

Some sources say IEEE754 floats are always stored little-endian but The IEEE754 specification for floating point numbers simply doesn't cover the endianness problem and may vary from machine to machine. Here is sample code for floating point / byte array conversion:

#include <stdio.h>

int main(int argc, char** argv){
  char *a;
  float f = 3.14159;  // number to start with

  a = (char *)&f;   // point a to f's location

  // print float & byte array as hex
  printf("float: %f\n", f);
  printf("byte array: %hhX:%hhX:%hhX:%hhX\n", \
    a[0], a[1], a[2], a[3]);

  // toggle the sign of f -- using the byte array
  a[3] = ((unsigned int)a[3]) ^ 128;

  //print the numbers again
  printf("float: %f\n", f);
  printf("byte array: %hhX:%hhX:%hhX:%hhX\n", \
    a[0], a[1], a[2], a[3]);

  return 0;
}

It's output on a little-indian machine:

float: 3.141590 byte array: D0:F:49:40 float: -3.141590 byte array: D0:F:49:C0

Theoretically, on a big-endian machine the order of bytes would be reversed.

Reference: http://betterexplained.com/articles/understanding-big-and-little-endian-byte-order/