[Icc-avr] Casting

[Johannes Assenbaum]

Thank you, Albert.

I think there has been too much emphasis on not only the endians in this thread, too. I mean, this thread actually was started with an obviously array related question about programming an AVR - at90usb162 as posted before by same author -, and far away from excusing sloppy programming, endians and portability never will be really interesting if I'm coding for unique parts like USB AVRs... 

Johannes


> I think there has been too much emphasis on the endians in this thread.
> Nearly always these conversions are wanted for storage in byte-arrays or
> comms buffers, and as long as storing and retrieving uses the same
> method (and a few were mentioned here!) it doesn't matter where msb or
> lsb is. Using Motorola (oops.. Freescale), TMS, PIC & AVR, I haven't
> stumbled over it yet.
> I hope this doesn't upset Ton's "There is no excuse for sloppy
> programming." in which he is perfectly correct of course.

> Albert.

> -----Original Message-----
> From: icc-avr-bounces at imagecraft.com
> [mailto:icc-avr-bounces at imagecraft.com] On Behalf Of Johan H. Bodin
> Sent: Tuesday, January 15, 2008 09:50 PM
> To: Discussion list for ICCAVR and ICCtiny Users. You do NOT need
> tosubscribe to icc-announce if you are a member of this.
> Subject: Re: [Icc-avr] Casting

> This works for me:

> -----------
> #ifndef BYTEPICK_INCLUDED
> #define BYTEPICK_INCLUDED

> /***********************************/
> /*  Johan Bodin SM6LKM 2007-06-01  */
> /***********************************/

> // This should ideally be predefined by the compiler...:
> // ICCAVR7 uses little endian (LSByte first)

> #define LITTLE_ENDIAN
> //#define BIG_ENDIAN


> // Sanity check:

> #ifdef LITTLE_ENDIAN
> #ifdef BIG_ENDIAN
> #error "You can't have both endian types in bytepick.h!"
> #endif
> #endif

> #ifndef LITTLE_ENDIAN
> #ifndef BIG_ENDIAN
> #error "You must select big/little endian in bytepick.h!"
> #endif
> #endif


> // Here we go:

> #ifdef BIG_ENDIAN

> #define HIGH_BYTE_32(longvar)   (*((unsigned char *)(&longvar)))
> #define MID_H_BYTE_32(longvar)  (*((unsigned char *)(&longvar) + 1))
> #define MID_L_BYTE_32(longvar)  (*((unsigned char *)(&longvar) + 2))
> #define LOW_BYTE_32(longvar)    (*((unsigned char *)(&longvar) + 3))

> #define HIGH_BYTE_16(shortvar)  (*((unsigned char *)(&shortvar)))
> #define LOW_BYTE_16(shortvar)   (*((unsigned char *)(&shortvar) + 1))

> #else

> #define HIGH_BYTE_32(longvar)   (*((unsigned char *)(&longvar) + 3))
> #define MID_H_BYTE_32(longvar)  (*((unsigned char *)(&longvar) + 2))
> #define MID_L_BYTE_32(longvar)  (*((unsigned char *)(&longvar) + 1))
> #define LOW_BYTE_32(longvar)    (*((unsigned char *)(&longvar)))

> #define HIGH_BYTE_16(shortvar)  (*((unsigned char *)(&shortvar) + 1))
> #define LOW_BYTE_16(shortvar)   (*((unsigned char *)(&shortvar)))

> #endif

> #endif // BYTEPICK_INCLUDED

> -----------

> Regards
> Johan Bodin

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