#include <stdarg.h>
#include <stdint.h>

enum TYPE {
  TYPE_INT    = 1,
  TYPE_UINT   = 2,
  TYPE_HEX    = 3,
  TYPE_STRING = 4
};

static void hex(char **str, int x) {
  int n;
  char *s = "0x";

  while(*s)
    *(*str)++ = *s++;

  n = sizeof(x) << 1;
  while(n--) {
    *(*str)++ = ((unsigned int) x >> 28) + 0x30;
    x = x << 4;
  }
}

int vsprintf(char *str, char *fmt, va_list ap) {
  int x;
  char *s;
  char *start = str;
  uint8_t type;

  while(*fmt) {
    if(*fmt != '%') {
      *str++ = *fmt++;
      continue;
    }

    type = 0;

    fmt++;    
    while(1) {
      switch(*fmt) {
        case 's':
          if(type)
            goto done;
          type = TYPE_STRING;
          break;
        case 'x':
          if(type)
            goto done;
          type = TYPE_HEX;
          break;
        default:
          goto done;
          break;
      }
      fmt++;
    }

done:

    switch(type) {
      case TYPE_STRING:
        s = va_arg(ap, char*);
        while(*s)
          *str++ = *s++;
        break;
      case TYPE_HEX:
        x = va_arg(ap, int);
        hex(&str, x);
        break;
    }
  }

  *str = 0;

  return (str - start);
}