Path: utzoo!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!mdcbbs!halloran
From: halloran@mdcbbs.com (M. J. Halloran II (McDonnell Douglas M&E))
Newsgroups: comp.lang.c
Subject: Define Big/Little Endian ( was: Re: RISC Mach...)
Message-ID: <686.25c92d5f@mdcbbs.com>
Date: 2 Feb 90 06:49:02 GMT
References: <111@melpar.UUCP> <6200024@ux1.cso.uiuc.edu>
Organization: McDonnell Douglas M&E, Cypress CA
Lines: 37

In article <6200024@ux1.cso.uiuc.edu>, phil@ux1.cso.uiuc.edu writes:
> Another problem you can encounter when dealing with data structure formats
> imposed by hardware, particularly external hardware, is the byte order.
> An example is handling TCP and IP headers.  The exact data structure is
> defined very specifically, but making code that can deal with it AND be
> portable across big and little endian machines requires a lot of care.
                  ---     ------ ------
		   Let's clerify...
> Such portable code may not be the most optimal depending on how it is
> done.
> 
> --Phil Howard, KA9WGN--
> <phil@ux1.cso.uiuc.edu>

   These define how bytes within words are ordered.

Big endian:    Big end first (MSB)(LSB).
Little endian: Little end first (LSB)(MSB).

	ie: 

	typedef union {
		unsigned char bytes[2];
		unsigned long word;
	    } INDIANS;

	main()	{

	        INDIAN indian;

	    indian.word = 0x1234;

	    if ( indian.bytes[0] == 0x12) /* is MSB at lower mem? */
		puts ( "Big Endian\n");
	    else
		puts ( "Little Endian\n");
	}