🚀 go-pugleaf

Jordi Canton <canton@eq.upc.es> wrote:
: Alguien conoce alguna manera elegante y eficiente de invertir el orden
: de todos los bits de un byte en C?

	elegante, yo diria que no.
	Eficiente, con una tabla.


: b0 b1 b2 b3 b4 b5 b6 b7

: y quiero obtener un byte con los bits de esta otra forma:

: b7 b6 b5 b4 b3 b2 b1 b0


---------------------------------------------------------------------------
#include <stdio.h>


#define invert_byte(a) ( \
	((unsigned char)(a&0x80) >> 7) |\
	((unsigned char)(a&0x40) >> 5) |\
	((unsigned char)(a&0x20) >> 3) |\
	((unsigned char)(a&0x10) >> 1) |\
	((unsigned char)(a&0x08) << 1) |\
	((unsigned char)(a&0x04) << 3) |\
	((unsigned char)(a&0x02) << 5) |\
	((unsigned char)(a&0x01) << 7) \
	)
	

char *out_c(unsigned char c);
static char s[9];

main()
{
	unsigned char c=0;

	do
	{
		printf ( "%0.3d\t", c);
		printf ( "%s\t", out_c(c));
		printf ( "%s\t", out_c(invert_byte(c)));
		printf ( "%0.3d\n", invert_byte(c));
		c++;
	}
	while ( c>0 );

	return(0);
} 

char *out_c(unsigned char c)
{
	char *p=s+7;

	do
	{
		*p-- = ( "01"[(c&0x01)] );
		c = c >> 1; 
	}
	while ( p>=s );
	return(s);
}

---------------------------------------------------------------------------



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