#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <limits.h>
#include <ctype.h>
#include <math.h>

/* some macros to cut this short
 * NEXT(c);     read next character
 * PREV(c);     ungetc a character
 * VAL(a)       leads to 1 if a is true and valid
 */
#define NEXT(c) ((c)=xgetc(opaque),size++,incount++)
#define PREV(c) do{if((c)!=EOF)xungetc(opaque,(c));size--;incount--;}while(0)
#define VAL(a)  ((a)&&size<=width)

#ifdef NOFLOATINGPOINT
#undef FULL_SPECIFIERS
#else
#define FULL_SPECIFIERS
#endif

extern unsigned char *__decimalpoint;

#ifdef FULL_SPECIFIERS
static const unsigned char undef[3][sizeof(double)]= /* Undefined numeric values, IEEE */
{ { 0x7f,0xf0,0x00,0x00,0x00,0x00,0x00,0x00 }, /* +inf */
  { 0xff,0xf0,0x00,0x00,0x00,0x00,0x00,0x00 }, /* -inf */
  { 0x7f,0xf1,0x00,0x00,0x00,0x00,0x00,0x00 }  /*  NaN */
};
#endif

int vxscanf(int (*xgetc)(void *),void (*xungetc)(void*,int),void *opaque,const char *format,va_list args)
{
  size_t blocks=0,incount=0;
  int c=0;

  while(*format)
  {
    size_t size=0;

    if(*format=='%')
    {
      size_t width=ULONG_MAX;
      char type,subtype='i',ignore=0;
      const unsigned char *ptr=(const unsigned char *)format+1;
      size_t i;

      if(isdigit(*ptr))
      { width=0;
	while(isdigit(*ptr))
	  width=width*10+(*ptr++-'0'); }

      while(*ptr=='h'||*ptr=='l'||*ptr=='L'||*ptr=='*')
      { if(*ptr=='*')
	  ignore=1;
	else
	  subtype=*ptr;
	ptr++;
      }

      type=*ptr++;

      if(type&&type!='%'&&type!='c'&&type!='n'&&type!='[')
      { do /* ignore leading whitespace characters */
	  NEXT(c);
	while(isspace(c));
	size=1; } /* The first non-whitespace character is already read */

      switch(type)
      { case 'c':
	{ unsigned char *bp;

	  if(width==ULONG_MAX) /* Default */
	    width=1;

	  if(!ignore)
	    bp=va_arg(args,unsigned char *);
	  else
	    bp=NULL; /* Just to get the compiler happy */

	  NEXT(c); /* 'c' did not skip whitespace */
	  while(VAL(c!=EOF))
	  { if(!ignore)
	      *bp++=c;
	    NEXT(c);
	  }
	  PREV(c);

	  if(!ignore&&size)
	    blocks++;
	  break;
	}
	case '[':
	{ unsigned char *bp;
	  unsigned char tab[32],a,b;
	  char circflag=0;

	  if(*ptr=='^')
	  { circflag=1;
	    ptr++; }
	  for(i=0;i<sizeof(tab);i++)
	    tab[i]=circflag?255:0;
	  for(;;)
	  { if(!*ptr)
	      break;
	    a=b=*ptr++;
	    if(*ptr=='-'&&ptr[1]&&ptr[1]!=']')
	    { ptr++;
	      b=*ptr++; }
	    for(i=a;i<=b;i++)
	      if(circflag)
		tab[i/8]&=~(1<<(i&7));
	      else
		tab[i/8]|=1<<(i&7);
	    if(*ptr==']')
	    { ptr++;
	      break; }
	  }

	  if(!ignore)
	    bp=va_arg(args,unsigned char *);
	  else
	    bp=NULL; /* Just to get the compiler happy */

	  NEXT(c);
	  while(VAL(c!=EOF&&tab[c/8]&(1<<(c&7))))
	  { if(!ignore)
	      *bp++=c;
	    NEXT(c);
	  }
	  PREV(c);

	  if(!ignore&&size)
	  { *bp++='\0';
	    blocks++; }
	  break;
	}
	case 's':
	{ unsigned char *bp;

	  if(!ignore)
	    bp=va_arg(args,unsigned char *);
	  else
	    bp=NULL; /* Just to get the compiler happy */

	  while(VAL(c!=EOF&&!isspace(c)))
	  { if(!ignore)
	      *bp++=c;
	    NEXT(c);
	  }
	  PREV(c);

	  if(!ignore&&size)
	  { *bp++='\0';
	    blocks++; }
	  break;
	}
#ifdef FULL_SPECIFIERS
	case 'e':
	case 'f':
	case 'g':
	{ double v;
	  int ex=0;
	  int min=0,mine=0; /* This is a workaround for gcc 2.3.3: should be char */

	  do /* This is there just to be able to break out */
	  {
	    if(VAL(c=='-'||c=='+'))
	    { min=c;
	      NEXT(c); }

	    if(VAL(tolower(c)=='i')) /* +- inf */
	    { int d;
	      NEXT(d);
	      if(VAL(tolower(d)=='n'))
	      { int e;
		NEXT(e);
		if(VAL(tolower(e)=='f'))
		{ v=*(double *)&undef[min=='-'];
		  break; } /* break out */
		PREV(e);
	      }
	      PREV(d);
	    }
	    else if(VAL(toupper(c)=='N')) /* NaN */
	    { int d;
	      NEXT(d);
	      if(VAL(tolower(d)=='a'))
	      { int e;
		NEXT(e);
		if(VAL(toupper(e)=='N'))
		{ v=*(double *)&undef[2];
		  break; }
		PREV(e);
	      }
	      PREV(d);
	    }

	    v=0.0;
	    while(VAL(isdigit(c)))
	    { v=v*10.0+(c-'0');
	      NEXT(c);
	    }

	    if(VAL(c==__decimalpoint[0]))
	    { double dp=0.1;
	      NEXT(c);
	      while(VAL(isdigit(c)))
	      { v=v+dp*(c-'0');
		dp=dp/10.0;
		NEXT(c); }
	      if(size==2+(min!=0)) /* No number read till now -> malformatted */
	      { PREV(c);
		c=__decimalpoint[0]; }
	    }

	    if(min&&size==2) /* No number read till now -> malformatted */
	    { PREV(c);
	      c=min; }
	    if(size==1)
	      break;

	    if(VAL(tolower(c)=='e'))
	    { int d;
	      NEXT(d);
	      if(VAL(d=='-'||d=='+'))
	      { mine=d;
		NEXT(d); }

	      if(VAL(isdigit(d)))
	      { do
		{ ex=ex*10+(d-'0');
		  NEXT(d);
		}while(VAL(isdigit(d)&&ex<100));
		c=d;
	      }else
	      { PREV(d);
		if(mine)
		  PREV(mine);
	      }
	    }
	    PREV(c);

	    if(mine=='-')
	      v=v/pow(10.0,ex);
	    else
	      v=v*pow(10.0,ex);

	    if(min=='-')
	      v=-v;

	  }while(0);

	  if(!ignore&&size)
	  { switch(subtype)
	    { case 'l':
	      case 'L':
		*va_arg(args,double *)=v;
		break;
	      case 'i':
		*va_arg(args,float *)=v;
		break;
	    }
	    blocks++;
	  }
	  break;
	}
#endif
	case '%':
	  NEXT(c);
	  if(c!='%')
	    PREV(c); /* unget non-'%' character */
	  break;
	case 'n':
	  if(!ignore)
	    *va_arg(args,int *)=incount;
	  size=1; /* fake a valid argument */
	  blocks++;
	  break;
	default:
	{ unsigned long v=0;
	  int base;
	  int min=0;

	  if(!type)
	    ptr--; /* unparse NUL character */

	  if(type=='p')
	  { subtype='l'; /* This is the same as %lx */
	    type='x'; }

	  if(VAL((c=='-'&&type!='u')||c=='+'))
	  { min=c;
	    NEXT(c); }

	  if(type=='i') /* which one to use ? */
	  { if(VAL(c=='0')) /* Could be octal or sedecimal */
	    { int d;
	      NEXT(d); /* Get a look at next character */
	      if(VAL(tolower(d)=='x'))
	      { int e;
		NEXT(e); /* And the next */
		if(VAL(isxdigit(c)))
		  type='x'; /* Is a valid x number with '0x?' */
		PREV(e);
	      }else
		type='o';
	      PREV(d);
	    }else if(VAL(!isdigit(c)&&isxdigit(c)))
	      type='x'; /* Is a valid x number without '0x' */
	  }

	  while(type=='x'&&VAL(c=='0')) /* sedecimal */
	  { int d;
	    NEXT(d);
	    if(VAL(tolower(d)=='x'))
	    { int e;
	      NEXT(e);
	      if(VAL(isxdigit(e)))
	      { c=e;
		break; } /* Used while just to do this ;-) */
	      PREV(e);
	    }
	    PREV(d);
	    break; /* Need no loop */
	  }

	  base=type=='x'||type=='X'?16:(type=='o'?8:10);
	  while(VAL(isxdigit(c)&&(base!=10||isdigit(c))&&(base!=8||c<='7')))
	  { v=v*base+(isdigit(c)?c-'0':0)+(isupper(c)?c-'A'+10:0)+(islower(c)?c-'a'+10:0);
	    NEXT(c);
	  }

	  if(min&&size==2) /* If there is no valid character after sign, unget last */
	  { PREV(c);
	    c=min; }

	  PREV(c);

	  if(ignore||!size)
	    break;

	  if(type=='u')
	    switch(subtype)
	    { case 'l':
	      case 'L':
		*va_arg(args,unsigned long *)=v;
		break;
	      case 'i':
		*va_arg(args,unsigned int *)=v;
		break;
	      case 'h':
		*va_arg(args,unsigned short *)=v;
		break;
	    }
	  else
	  { signed long v2;
	    if(min=='-')
	      v2=-v;
	    else
	      v2=v;
	    switch(subtype)
	    { case 'l':
	      case 'L':
		*va_arg(args,signed long *)=v2;
		break;
	      case 'i':
		*va_arg(args,signed int *)=v2;
		break;
	      case 'h':
		*va_arg(args,signed short *)=v2;
		break;
	    }
	  }
	  blocks++;
	  break;
	}
      }
      format=(const char *)ptr;
    }else
    { if(isspace(*format))
      { do
	  NEXT(c);
	while(isspace(c));
	PREV(c);
	size=1; }
      else
      { NEXT(c);
	if(c!=*format)
	  PREV(c); }
      format++;
    }
    if(!size)
      break;
  }

  if(c==EOF&&!blocks)
    return c;
  else
    return blocks;
}