8 bit Bitmanipulation casten, sonst 16 bit?

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http://www.nongnu.org/avr-libc/user-manual/FAQ.html#faq_intpromote :

Why *does* the *compiler* compile *an* 8-bit *operation* that 
uses *bitwise* operators *into* a *16-bit* operation *in* 
*assembly?*

Bitwise operations in Standard C will automatically promote their 
operands to an int, which is (by default) 16 bits in avr-gcc.

To work around this use typecasts on the operands, including literals, 
to declare that the values are to be 8 bit operands.

This may be especially important when clearing a bit:

1

var &= ~mask;  /* wrong way! */

The bitwise "not" operator (~) will also promote the value in mask to an 
int. To keep it an 8-bit value, typecast before the "not" operator:

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var &= (unsigned char)~mask;"