Swapping endiannes

This is a discussion on Swapping endiannes within the C Programming forums, part of the General Programming Boards category; Hello you all familiar with big-ednian and small-endian. With Motorola processors I stumbled on this little fact that values are ...

  1. #1
    Registered User Rennor's Avatar
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    Swapping endiannes

    Hello you all familiar with big-ednian and small-endian. With Motorola processors I stumbled on this little fact that values are in different byte orders in Motorola and Intel systems. Woot.

    So, I made small C function to swap 32bit integer values for my Cantata++ test platform while reading real binary file which is copied to memory and act's as embedded RAM/ROM during the test which is not connected to unit at all.

    Here's the function:
    Code:
    #define u32  unsigned __int32 // Definition for Cantata++
    #define u8 unsigned char
    
    u32 swap( u32 val )
    {
    	u32 temp, iLoop;
    	u8 *pDest = (u8 *)&temp;
    	u8 *pSrc = (u8 *)&val;
    
    	for( iLoop = 0; iLoop < sizeof( val ); iLoop++ )
    		*(pDest + iLoop) = *((pSrc+sizeof( val ))-(iLoop+1));
    
    	return temp;
    }
    Now, I believe this will cause alot of debate (which I am actually looking for). I know it is best to do things the way knowing it will work for sure. Why I didnt loop from 0 to 3? Why I used sizeof() instead? Well, I thought I could later on change this function to:

    void swap( u8 *val, u8 length );

    And replace sizeof() calls with length. That way I could call it:
    swap( (u8*)&myVar, sizeof( myVar ) );
    And this would work wonders for all my needs from 8bit to 64bit integers



    So why I post a question? I am sure theres allways more bright way to do things like this (maybe even optimized, faster ones... which I actually dont need) and am a bit interested... since this is really the best I can do atm.
    Last edited by Rennor; 09-05-2006 at 03:58 AM.

  2. #2
    ATH0 quzah's Avatar
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    htonl and its kin perhaps?


    Quzah.
    Hope is the first step on the road to disappointment.

  3. #3
    Registered User Rennor's Avatar
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    Quote Originally Posted by quzah
    htonl and its kin perhaps?
    Sorry I forgot to mention I run my tests using VC++ 6.0.

    Or should I feel silly by being unable to find htonl, htons, ntohl, ntohs with my compiler?

  4. #4
    ATH0 quzah's Avatar
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    You probably have them. Like you said though, there are plenty of ways to do the same thing, these are just some "not really standard but pretty common" functions which will work (if you have them that is).


    Quzah.
    Hope is the first step on the road to disappointment.

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