On Monday 30 May 2005 14:14, Larry Barello wrote:
> Ok, I submitted this as a bug (#21811) and within an hour it was closed as
> a duplicate of #8788 which will be corrected in the 4.1.0 mainline. #8788
> sounds similar, but I am still somewhat unsatisfied since a union of a
> three byte array and a word should be allowed in C. Maybe I just didn't
> understand.
You may use 3-bytes unions with implicit loading to registers.
For example (I am not remember an original code):
int foo (int i)
{
union {
unsigned int word;
unsigned char byte[3];
} u;
u.word = i;
u.byte[2] = 0;
asm (
"subi %0,-1 \n\t"
"sbci %1,-1 \n\t"
"sbci %2,-1 "
: "+d" (u.byte[0]), "+d" (u.byte[1]), "+d" (u.byte[2]) );
return u.byte[2];
}
produce next code (avr-gcc 3.3.4 -Os):
...
/* prologue end (size=10) */
std Y+1,r24
std Y+2,r25
std Y+3,__zero_reg__
ldd r18,Y+1
ldd r25,Y+2
ldd r24,Y+3
/* #APP */
subi r18,-1
sbci r25,-1
sbci r24,-1
/* #NOAPP */
clr r25
/* epilogue: frame size=3 */
...
Regards.
_______________________________________________
AVR-GCC-list mailing list
AVR-GCC-list@nongnu.org
http://lists.nongnu.org/mailman/listinfo/avr-gcc-list
