Print bits with x86_64 intrinsics

bitpr.c

/* Compile with "gcc -std=c23 -mbmi2 -mlzcnt" (gcc-14)
 *           or "gcc -std=c2x -mbmi2 -mlzcnt" (gcc-13)
 */
#include <errno.h>
#include <stdint.h>
#include <stdio.h>
#include <immintrin.h>

static void
bitpr (uint64_t n)
{
	uint64_t b[9] = {'0'};
	unsigned z = (typeof(z))__builtin_ia32_lzcnt_u64(n);

	for (typeof(z) i = (71U - z) >> 3U; i--;) {
		b[i] = __builtin_bswap64(UINT64_C(3472328296227680304)
			| (uint64_t)_pdep_u64(n, 72340172838076673ULL));

		if (!(n >>= 8U))
			break;
	}

	puts(&((char const *)&b[0])[z & 7U]);
}

int
main (int    c,
      char **v)
{
	for (int i = 0; ++i < c;) {
		char *p = v[i];
		if (!*p)
			continue;

		errno = 0;
		uint64_t n = _Generic(n,
			typeof(1UL): strtoul,
			typeof(1ULL): strtoull)(p, &p, 0);

		if (errno || *p)
			continue;

		bitpr(n);
	}
}