#include <ctype.h>
#include <stdlib.h>
#include <errno.h>
#include <limits.h>
#include <sys/cdefs.h>

unsigned long int strtoul(const char *ptr, char **endptr, int base)
{
	int neg = 0, overflow = 0;
	unsigned long int v=0;
	const char* orig;
	const char* nptr=ptr;

	while(isspace(*nptr)) ++nptr;

	if (*nptr == '-') { neg=1; nptr++; }
	else if (*nptr == '+') ++nptr;
	orig=nptr;
	if (base==16 && nptr[0]=='0') goto skip0x;
	if (base) {
		register unsigned int b=base-2;
		if (__unlikely(b>34)) { errno=EINVAL; return 0; }
	} else {
		if (*nptr=='0') {
			base=8;
		skip0x:
			if ((nptr[1]=='x'||nptr[1]=='X') && isxdigit(nptr[2])) {
				nptr+=2;
				base=16;
			}
		} else
			base=10;
	}
	while(__likely(*nptr)) {
		register unsigned char c=*nptr;
		c=(c>='a'?c-'a'+10:c>='A'?c-'A'+10:c<='9'?c-'0':0xff);
		if (__unlikely(c>=base)) break;	/* out of base */
		{
			register unsigned long x=(v&0xff)*base+c;
			register unsigned long w=(v>>8)*base+(x>>8);
			if (w>(ULONG_MAX>>8)) overflow=1;
			v=(w<<8)+(x&0xff);
		}
		++nptr;
	}
	if (__unlikely(nptr==orig)) {		/* no conversion done */
		nptr=ptr;
		errno=EINVAL;
		v=0;
	}
	if (endptr) *endptr=(char *)nptr;
	if (overflow) {
		errno=ERANGE;
		return ULONG_MAX;
	}
	return (neg?-v:v);
}