Re: [Dev-C++] Convert Little-Endian to Big-Endian (and vice versa)

[Joey D. <jda...@ya...>]

can you please give me a code snippet.
i have no idea what's  in your mind.

thanks.

 --- William Mc Coy <WIL...@ms...> wrote: 
> You might also want to look at using "exclusive OR"
> on each byte.
>   ----- Original Message ----- 
>   From: Daniel K.
> O.<mailto:dan...@ya...> 
>   To: Joey Dala<mailto:jda...@ya...> 
>   Cc:
>
dev...@li...<mailto:dev...@li...>
> 
>   Sent: Thursday, November 11, 2004 10:34 AM
>   Subject: Re: [Dev-C++] Convert Little-Endian to
> Big-Endian (and vice versa)
> 
> 
>   Joey Dala wrote:
> 
>   > Does anybody know a faster algorithm to swap the
> bytes
>   > of an 'unsigned long' than this:
>   >  
>   > // SWAP 32-BITS
>   > #define SWAP_LONG( A )  ((A << 24) | ((A &
> 0xff00L) << 8 ) | ((A & 
>   > 0xff0000L) >> 8 ) | ((unsigned long)A >> 24))
> 
> 
>   Faster than this? Only if you use
> architecture-specific instructions. 
>   The 486 (and higher) family has the "bswap"
> instruction. Here's an example:
> 
>   ---
>   #include <stdio.h>
> 
>   #define SWAP32(x)      asm volatile ("bswap %0" :
> "=r" (x) : "0" (x))
> 
>   int main(void)
>   {
>           int foo = 1;
>    
>           printf("%08x\n", foo);
>    
>           asm volatile (
>                   "bswap %0"
>                   : "=r" (foo)
>                   : "0" (foo)
>                   );
>          
>           printf("%08x\n", foo);
> 
>           SWAP32(foo);
> 
>           printf("%08x\n", foo);
> 
>           getchar();
>           return 0;
>   }
>   ---
> 
>   Notice the use of the extended assembly syntax, so
> GCC can perform 
>   better optimizations around the asm beast.
>   Also, the "volatile" keyword to make sure GCC
> won't move the assembly 
>   statement around in the optimization proccess.
> 
> 
>   Before you ask, some information about using AT&T
> assembly syntax and 
>   extended syntax is available here: 
>  
>
http://www.delorie.com/djgpp/doc/brennan/brennan_att_inline_djgpp.html<http://www.delorie.com/djgpp/doc/brennan/brennan_att_inline_djgpp.html>
> 
> 
>   Daniel K. O.
> 
> 
> 
>  
>
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