Re: [ECOS] Network programming for eCos under linux

[Jonathan Larmour <jlarmour at redhat dot com>]

"Trenton D. Adams" wrote:
> 
>   >
>   > > So, how would one go about making a buffer word aligned or DWORD
>   > aligned
>   > > just to be safe?
>   >
>   > something along the lines of:
>   >
>   > char buffer[1024];
>   > #define ALIGNMENT 8
>   > #define ALIGNUP(_x_) (((char *)(_x_) + ALIGN-1) & ~(ALIGN-1))
>   > int *foo = ALIGNUP(buffer);
>   >
>   > You could also use __alignof(int) to give the alignment but that's
>   > obviously a GNU C-ism.
>   >
> 
> First of all, I assume your ALIGN is actually supposed to be ALIGNMENT!

Oops yes.
 
> I don't understand your macro.  Let's say _x_ happens to be memory
> address 0x201 the macro formula would go like this
> 
> = (0x201 + 7) & ~(7)
> = 0x208 & 0xfffffff8
> = 0x208
> 
> So, now foo is pointing to an integer that is not at the beginning of
> the buffer.  This would mean that I couldn't put anything at the
> beginning of the buffer, correct?

If 8 byte alignment was the requirement then you certainly wouldn't want
to. I suppose in that case you would make the buffer be 1031 bytes to
ensure it could fit 1024 bytes post alignment.

Jifl
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