[Icc-avr] Casting

[Johannes Assenbaum]

I don't beleive in "high" and "low" operators to be really useful at c level, because compiler basically is free to generate different code depending on (default) int size. I.e. with int=16bits, high() and low() may result in bytes, but with int=32bits you'll get 16bit words.

Whereas "XXX >> 8" always is meaning byte shift for compiler as well as for coder/reader.

Superfluous instructions can be expected to be omitted by compiler anyway. (as by iccavr.)

Johannes


> Some compilers have operators like "high()" and "low()", which makes it
> clear to the compiler (and to the reader) that that is exactly the
> simple thing that you want: just use the appropriate address and no
> superfluous instructions.

> Albert.


> -----Original Message-----
> From: icc-avr-bounces at imagecraft.com
> [mailto:icc-avr-bounces at imagecraft.com] On Behalf Of Johannes Assenbaum
> Sent: Tuesday, January 15, 2008 08:41 AM
> To: icc-avr at imagecraft.com
> Subject: Re: [Icc-avr] Casting

> As someone mentioned before, this is only safe for Little Endian, but as
> AVRs are Little Endian, there will be no problem with iccavr.

> Btw: Shortest code (no optimisation enabled) will be with source value
> casted.

> Data[7] = ((unsigned int)(Channel_One) >> 8); Data[8] = ((unsigned
> int)(Channel_One));

> Best regards,
> Johannes


>>> Andrew wrote:
>>>> Hi,
>>>>
>>>> When casting and int to two char' (a MSB and LSB) is it safe to do
>>>> the
>>>> following:-
>>>> Data[7] = (Channel_One >> 8);
>>>> Data[8] = (Channel_One);
>>>>

>> I always use the above solution, it should be perfectly legal and it
>> has never failed me on any compiler. I think it is quite clear for any

>> programmer of embedded systems what this does.

>> regards
>> Johan


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