simple macros to extract u{8,16,32}'s from variables.

bitslice.c

/*
 * bitslice.c
 * build with gcc -Wall.
 *
 * simple macros to extract u{8,16,32}'s from variables.
 */
#include <stdint.h>
#include <stdio.h>

#define __shift(n, log)	((n) << (log))

#define logmask(log)	((1ULL << (1 << (log))) - 1)
#define __get_slice(x, n, log)					\
	(((x) >> __shift((n), (log))) & logmask(log))

#define get_u8(x, n)	__get_slice((x), (n), 3)
#define get_u16(x, n)	__get_slice((x), (n), 4)
#define get_u32(x, n)	__get_slice((x), (n), 5)

int main(int argc, char *argv[])
{
	unsigned long long val = 0xcafebabedeadbeef;
	uint8_t		getu8[8];
	uint16_t	getu16[8];
	uint32_t	getu32[8];
	int i, j;

	printf("u64\t%llx\n", val);

	printf("u32\t");
	for (i = 0; i < sizeof(val) / sizeof(getu32[0]); i++) {
		j = 7 - i;
		getu32[i] = get_u32(val, j);
		printf("%x ", getu32[i]);
	}
	printf("\n");

	printf("u16\t");
	for (i = 0; i < sizeof(val) / sizeof(getu16[0]); i++) {
		j = 7 - i;
		getu16[i] = get_u16(val, j);
		printf("%x ", getu16[i]);
	}
	printf("\n");

	printf("u8\t");
	for (i = 0; i < sizeof(val) / sizeof(getu8[0]); i++) {
		j = 7 - i;
		getu8[i] = get_u8(val, j);
		printf("%x ", getu8[i]);
	}
	printf("\n");

	return 0;
}