Convert a number from base power of 2 to decimal.

bpt2dec.c

#include <stddef.h>
#include <stdio.h>

/* Base power of 2 to decimal */
static unsigned bpt2dec(unsigned x, size_t mask) {
	int indec = 0;
    const int bits = __builtin_popcount(mask);
	for (int i = 0; x != 0; ++i, x >>= bits)
		indec += ((x & mask) << (i * bits));
	return indec;
}

static inline unsigned hex2dec(unsigned x) {
    return bpt2dec(x, 0xf);
}

static inline unsigned oct2dec(unsigned x) {
    return bpt2dec(x, 07);
}

static inline unsigned bin2dec(unsigned x) {
    return bpt2dec(x, 0b1);
}

int main()
{
   printf("hex2dec(0xffff) = %lu\n", hex2dec(0xffff));
   printf("oct2dec(077) = %lu\n", oct2dec(077));
   printf("bin2dec(0b1010) = %lu\n", bin2dec(0b1010));
   return 0;
}