Re: [Algorithms] Byte Swapping

[Michael S. H. <mic...@ud...>]

Just for good measure, here's ours

/*
  useful macros for swapping 16 and 32 bit data types
*/
#define MAKE16(l, h)    ((Uint16)(((Byte)(l)) | ((Uint16)((Byte)(h))) << 8))
#define MAKE32(l, h)    ((Uint32)(((Uint16)(l)) | ((Uint32)((Uint16)(h))) << 16))
#define LO16(l)                 ((Uint16)(l))
#define HI16(l)                 ((Uint16)(((Uint32)(l) >> 16) & 0xFFFF))
#define LO8(w)                  ((Byte)(w))
#define HI8(w)                  ((Byte)(((Uint16)(w) >> 8) & 0xFF))


/* these assume that the swapping is from motorola to intel format */
#if __cplusplus
#if NEEDBYTESWAP
        inline Int16 ByteSwap( Int16 &x )
        {
                Uint16 y                = (Uint16)x;
                y       = (Uint16)(y >> 8 | (y << 8 & 0xff00));
                x       = (Int16 &)y;
                return x;
        }
        inline Uint16 ByteSwap( Uint16 &x )
        {
                x       = (Uint16)(x >> 8 | (x << 8 & 0xff00));
                return x;
        }
        inline Int32 ByteSwap( Int32 &x )
        {
                Uint32 y                = (Uint32)x;
                y       = y >> 24 | (y >> 8 & 0xff00) | (y << 8 & 0xff0000) | (y << 24 & 0xff000000);
                x       = (Int32 &)y;
                return x;
        }
        inline Uint32 ByteSwap( Uint32 &x )
        {
                x       = x >> 24 | (x >> 8 & 0xff00) | (x << 8 & 0xff0000) | (x << 24 & 0xff000000);
                return x;
        }
        template<class T> inline T ByteSwap( T &parm )
        {
                Uint32 x        = (Uint32)parm;
                x       = x >> 24 | (x >> 8 & 0xff00) | (x << 8 & 0xff0000) | (x << 24 & 0xff000000);
                parm = (T &)x;
                return parm;
        }
        inline float ByteSwap( float &x )
        {
                Uint32 * pTemp  = (Uint32*)&x;
                Uint32 y                = *pTemp;
                y       = y >> 24 | (y >> 8 & 0xff00) | (y << 8 & 0xff0000) | (y << 24 & 0xff000000);
                pTemp = (Uint32*)&y;
                x       = *((float*)pTemp);
                return x;
        }
        inline double ByteSwap( double &x )
        {
                Uint32 * pParm  = (Uint32*)&x;
                Uint32 nFirst   = pParm[0];
                Uint32 nSecond  = pParm[1];

                ByteSwap( nFirst );
                ByteSwap( nSecond );

                pParm[0] = nSecond;
                pParm[1] = nFirst;

                return x;
        }
#else
        #define ByteSwap(x) (x)
#endif
#endif /* __cplusplus */


At 03:41 PM 7/17/00, you wrote:

>Jumping in late : I'm sure you don't need it now, but
>here's a crazy ANSI C byte-swapper :
>
>let x = a 32 bit ulong , ABCD 
>then y = DCBA
>
>y = (x = x>>16 | x<<16) ^ (x = (x^x>>8) & 0x00FF00FF) ^ (x<<8);
>
>At 11:45 PM 7/15/2000 -0700, you wrote:
>>I can do the obvious method, but I was wondering if anyone have any 
>>cool/fast code snippets for byte swapping integers and floats?
>>
>>Tom
>>
>>
>>_______________________________________________
>>GDAlgorithms-list mailing list
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>>http://lists.sourceforge.net/mailman/listinfo/gdalgorithms-list
>>
>>
>--------------------------------------
>Charles Bloom           www.cbloom.com
>
>
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