#include <ctype.h>
#include <stdlib.h>
#include <errno.h>
#include <limits.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);
}
