Programming Embedded Systems, 2nd Edition

Endian Issues

Endianness is the attribute of a system that indicates whether integers are represented from left to right or right to left. Why, in today’s world of virtual machines and gigaHertz processors, would a programmer care about such a silly topic? Well, unfortunately, endianness must be chosen every time a hardware or software architecture is designed, and there isn’t much in the way of natural law to help in the decision.

Endianness comes in two varieties: big and little. A big-endian representation has a multibyte integer written with its most significant byte on the left; a number represented thus is easily read by English-speaking humans. A little-endian representation, on the other hand, places the most significant byte on the right. Of course, computer architectures don’t have an intrinsic “left” or “right.” These human terms are borrowed from our written forms of communication. The following definitions are more precise:

Big-endian

Means that the most significant byte of any multibyte data field is stored at the lowest memory address, which is also the address of the larger field

Little-endian

Means that the least significant byte of any multibyte data field is stored at the lowest memory address, which is also the address of the larger field

The origin of the odd terms big-endian and little-endian can be traced to the 1726 book Gulliver’s Travels, by Jonathan Swift. In one part of the story, resistance to an imperial edict to break soft-boiled eggs ...