#include <errno.h>
#include <stdint.h>

/** `printf`-compatible substring. */
struct substring { const char *sub; int size; };

/** Parse unsigned; [`s`,`e`) => `n`. */
static int helper_natural(const char *s, const char *const e, uint32_t *const n)
{
	uint32_t accum = 0;
	while(s < e) {
		unsigned next = accum * 10 + (unsigned)(*s - '0');
		if(accum >= next) return errno = ERANGE, 0;
		accum = next;
		s++;
	}
	*n = accum;
	return 1;
}

static void unused_helper_coda(void);
static void unused_helper(void)
	{ helper_natural(0, 0, 0); unused_helper_coda(); }
static void unused_helper_coda(void) { unused_helper(); }