[Fwd: Endian'ess.]

[amith <amith@multitech.co.in>]

-------- Original Message --------
Subject: Endian'ess.
Date: Thu, 08 Jul 2004 12:30:56 +0530
From: amith <amith@multitech.co.in>
To: KERNEL <kernelnewbies@nl.linux.org>



Hi all ,
             a little off-topic.            

#include
#include

typedef struct test
{
   unsigned short w1;
   unsigned short w2;
}Test;

Test t1;

unsigned long temp = 0x12345678;

main()
{
   printf(" sizeof(Test) = %d\n",sizeof(Test));
   memcpy(&t1,&temp,4);
   printf(" t1.w1 = %X \n",t1.w1);
   printf(" t1.w2 = %X \n",t1.w2);
   printf(" &t1.w1 = %X \n",&t1.w1);
   printf(" t1.w2 = %X \n",&t1.w2);
}

output:
t1.w1 = 5678
Typo > t1.w1 = 1234
shud be > t1.w2 = 1234
&t1.w1 =  6004
Typo > &t1.w1 =  6006  
shud be >&t1.w2 = 6006.


i tried the above code on  x86 and ARM , both gave me the same results. 
Both x86 and ARM are little-endian , or arent they? . Could someone 
explain this result with respect to the definition of Little Endian . 
which goes (one of them) as :
Little Endian: the least significant byte of a multi-byte data field is 
stored in the lowest memmory address.

Now, i have a couple of doubts :
1) i read somewhere on the net, that a processor can be set to either 
Little endian or Big endian, configurable ?
2) Could someone explain this with respect to the Little Endian 
definition given above.


 6004             6006
_________________
|    5678    |   1234      |
|________|________ |
t1.w1          t1.w2

Any good links to the Endianess would be great.

thanks.

cheers,
Amith





--
Kernelnewbies: Help each other learn about the Linux kernel.
Archive:       http://mail.nl.linux.org/kernelnewbies/
FAQ:           http://kernelnewbies.org/faq/