Re: [avr-gcc-list] mass stupidity with registers and longs

[Peter Bosscha]

Hi,
 
I've been using the following (don't have 3.4.1, but should simply work
?)

typedef union {
    long l;
    struct {
        unsigned char byte0,byte1,byte2,byte3;
    };
} longbytes;
 
----
 
longbytes ul;
unsigned char a,b,c,d;
 

  ul.l = 0;
  ul.byte0 = d;
  ul.byte1 = a;
  
  etc...
  
 
Advantage is also that this seems to produce the most efficient code.
 
---
 
Peter Bosscha

>>> Curtis Maloney <address@hidden> 14/01/2005 06:51:59 >>>


I give up.  I've been trying to shift 4 chars into an unsigned long,
but can't 
stop GCC 3.4.1 (what's shipped with the latest WinAVR) from sign
extending 
values, let alone producing sane code.

I've tried -Os, -O2, -O3, with and without -fnew-ra... the asm varies,
but is 
generaly crap.

now, if I have:
    extern char a[4];
    unsigned long ul;

    ul = ( (unsigned)a[0] << 8 ) | (unsigned)a[1];

why would it be sign extending a[0] and a[1] when they're cast to
unsigneds?
And then why doesn't the code optimiser see to just mov rX, a[1]; mov
rX+1,a[0] ?

I tried casts on casts on casts... everything I could think of to get
better 
code, and it just did not improve.

Am I missing something, or do I just need to get gcc 3.4.3?  If so, is
anyone 
lurking here involved with WinAVR, and can tell me when the next update
might 
happen?

--
Curtis Maloney


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