printf 함수의 소스입니다. 무슨버그가있는지?

http://library.kldp.net
의 프로젝트로 진행되는 소스입니다.
축약형 printf 인데,(이기종(arm,avr,msp430...etc) cpu 에 들어갈 예정)
그냥 찜찜해서 한번 올려봅니다. 무언가 버그가 있어보이는데
짜고나니 -_- 코드보기가 조금 싫어져서
또 여러 고수님들의 의견도 듣고싶고... 잠정적 문제점이라던가..
아직은 프로젝트가 활성화 되질 않아서 이곳이 좋아보이네요^^

#include <stdafx.h>

/*

  Small printf function

  //TODO
  Support a print with formatted;
  Support hash prefix (like 0x,o,b,...)

  prefix flag

  l : long
  # : hash prefix (not support now)

  %b : print binary number from variable
  %c : print character from variable
  %d : print signed decimal number from variable
  %u : print unsigned decimal number from variable
  %s : print string from variable pointer
  %o : print octal number from variable
  %x : print hexdecimal number form variable
  %X : print upper case hexdecimal number from variable

*/
int printf_(const char *formatstr,...)
{
	// define with maximum bytes + NULL;
	unsigned char buf[33];

	//for fast processing, using register var.
	register unsigned char *f;					// format string
	register unsigned char *bp;				// for buffer pointer skillz!
	register unsigned char fmst;				// real format string like b,c,d,s,x,X...
	register unsigned char do_long;				// get a (long) type flag.
	register unsigned char sign;				// plus or minus?
	register unsigned char div;					// divider;
	register unsigned char i;					// wide using

	register long l;
	register unsigned long u;
	//register unsigned char fcount;				// format count '%'

	//declare with a va_list struct;
	va_list ap;
	
	//define a stack bottom of args;
	va_start(ap,formatstr);

	//initialize
	//fcount = 0;
	do_long = 0;
	sign = 0;
	div = 0;
	i = 0;

	//pointer is void, so casting with uchar*
	f = (unsigned char*)formatstr;

	//get variable argument's count
	do
	{
		if(*f != '%')
		{
			putchar(*f);
		}
		else if(*f == '%')
		{
			f++;	// to meet a next character 'format string'

			if(*f == 'l')		// like %ld format string
			{
				do_long = 1;
			}

			fmst = *f;	// real format string like b,c,d,s,x,X...
			bp = buf;	// buffer pointer, and buffer

			switch(fmst)
			{
				case '%':
					putchar('%');
					break;
				case 'b':
					l = (long)va_arg(ap,int);

					if(l<0)
					{
						sign = 1;
						l = -l;
					}

					do
					{
						*bp++ = l%2 + '0';
					}while((l/=2) != 0);

					if(sign == 1)
					{
						*bp++ = '-';
					}

					for(bp--;bp>=buf;bp--)
					{
						putchar(*bp);
					}

					break;
				case 'c':
					i = va_arg(ap,unsigned char);
					putchar(i);
					break;
				case 'd':		// format str 'd' is signed decimal

					if(do_long == 1)
					{
						l = va_arg(ap,long);
					}
					else
					{
						l = (long)(va_arg(ap,int));
					}
					
					if(l<0)
					{
						sign = 1;
						l = -l;		//negative to positive
					}

					do
					{
						*bp++ = l%10 + '0';
					}while((l/=10) > 0);

					if(sign == 1)
					{
						*bp++ = '-';
					}

					for(bp--;bp>=buf;bp--)
					{
						putchar(*bp);
					}

					break;

				case 'o':
				case 'u':
				case 'x':
				case 'X':

					if(do_long == 1)
					{
						u = va_arg(ap,unsigned long);
					}
					else if(do_long == 0)
					{
						u = (unsigned long)(va_arg(ap,unsigned));
					}
					else;//Unknown error!?

					if(fmst == 'u')
					{
						div = 10;
					}
					else if(fmst == 'o')
					{
						div = 8;
					}
					
					if(fmst == 'x' || fmst == 'X')
					{
						// if HEX decimal
						do
						{
							i = u%16;
							if(i<10)
							{
								*bp++ = i+'0';
							}
							else
							{
								if(fmst == 'x')
									*bp++ = i-10 + 'a';
								else if(fmst == 'X')
									*bp++ = i-10 + 'A';
							}
						}while((u/=16) > 0);
					}
					else
					{
						// if not HEX decimal
						do
						{
							*bp++ = u%div + '0';
						}while((u/=div) > 0);
					}

					for(bp--;bp>=buf;bp--)
						putchar(*bp);
					//	putchar((int)*bp);

					break;

				case 's':
					bp = va_arg(ap,unsigned char*);

					if(!bp)
					{
						bp = (unsigned char*)"(NULL)\0";
					}

					while(*bp != '\0')
					{
						// Something dangerous?
						putchar(*bp);
						bp++;
					}

					break;

				default:
					break;
			}
		}
		else
		{
		}
	}while(*f++ != '\0');

	//rprintfNum_(10,fcount,2,' ');
}