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From: mcdonald@aries.scs.uiuc.edu (Doug McDonald)
Newsgroups: comp.arch
Subject: Re: Scalar vs Superscalar
Message-ID: <1991May11.012649.24340@ux1.cso.uiuc.edu>
Date: 11 May 91 01:26:49 GMT
References: <729@adpplz.UUCP> <1991May6.152803.5886@midway.uchicago.edu>
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In article <729@adpplz.UUCP> martin@adpplz.UUCP (Martin Golding) writes:
>In comp.arch you write: 
>>P.S.  could somebody email me a definition of "little endian" vs.
>>"big endian" ?  
>
>
>Careful, you're into religious mysteries here.

There is nothing religious about it. It is simply a fact.

 The terms refer to the
>(holy) significance of bytes within larger structures (eg, words).
>If you have the address of say, a 32 bit word (addressed byte plus
>the bytes at the next three incrementing addresses) little endian 
>means that the addressed byte is the least significant, big endian 
>means the addressed byte is the most significant.

That is correct.


>Big endian is also 
>referred to as "byte normal", and little endian "byte perverse" ;-)
>
NO!!! You have it reversed! See, there, you can get flamed too.


It is easy to understand: if you have, in C,
union {
unsigned char c;
unsigned int i;
unsigned long l;
} x;

and the value of x.i is <= 255, then on a little endian machine, so
is the value of x.c and x.l. Not so on big endian. 

On the other hand, ordered byte string compare instructions work 
properly on longs and ints on big endian but not little endian.


So, without the flames, it is a tossup. Of course, about 85% of the computers
in the world are little endian. 


Also, it is possible to design word oriented computers that simply
HAVE no endianness. 


Doug MCDonald