AVR-Chat

Original Message:
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David VanHorn wrote
>> I share your pain when you look at what the compiler's done, compared to
>> how you can do it in asm. You just have to breathe deeply and let it go.
>> If you're really strapped for execution time, you can write bits of it
>> in asm.
>
>And they told me and told me that C is can generate code that's "just
>as good" as a human..
>I thought they meant some non-random human...

Depending on architecture, compiler and human, the human can produce better
code over a 'short' stretch.  The compiler's advantage is over longer
stretches, more complex code and architectures.

>> Don't even think about trying to use part of a byte as a variable and
>> part for flags. You can do it, but it starts to negate all the reasons
>> for writing in C in the first place.
>
>Why?
>
>I might be using the wrong terms here, but it seems to me like just
>another sort of struct.

Right terms, think of bit fields.

struct {
    unsigned char index : 3;
    unsigned char type : 5;
    } bfld;

bfld.index++;  /* increments and wraps index */

Key questions, 
   does GCC allow unsigned char in this context? It's a common extension.
   does GCC allocate a single byte in this context? 

Robert


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> Right terms, think of bit fields.

Cool, I haven't read about bit fields yet.

> Key questions,
>   does GCC allow unsigned char in this context? It's a common extension.
>   does GCC allocate a single byte in this context?

I guess I'll find out.