OrionLibC

#include <stdarg.h>
#include <string.h>

#define is_digit(c)	((c) >= '0' && (c) <= '9')

/* Do not convert */
static int
skip_atoi(const char **s)
{
	int i = 0;

	while (is_digit(**s))
		i = i*10 + *((*s)++) - '0';

	return i;
}

#define ZEROPAD	1		/* pad with zero */
#define SIGN	2		/* unsigned/signed long */
#define PLUS	4		/* show plus */
#define SPACE	8		/* space if plus */
#define LEFT	16		/* left justified */
#define SPECIAL	32		/* 0x */
#define SMALL	64		/* use 'abcdef' instead of 'ABCDEF' */

#define do_div(n,base) ({ \
int __res; \
__asm__("divl %4":"=a" (n),"=d" (__res):"0" (n),"1" (0),"r" (base)); \
__res; })

/* Convert a number to ASCII */
static char *
number(char *str, int num, int base, int size, int precision, int type)
{
	char c, sign, tmp[36];
	const char *digits = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
	int i;

	if (type & SMALL)
		digits = "0123456789abcdefghijklmnopqrstuvwxyz";
	if (type & LEFT)
		type &= ~ZEROPAD;
	if (base < 2 || base > 36)
		return 0;
	c = (type & ZEROPAD) ? '0' : ' ' ;
	if (type & SIGN && num < 0) {
		sign = '-';
		num = -num;
	} else {
		sign = (type & PLUS) ? '+' : ((type & SPACE) ? ' ' : 0);
	}
	if (sign)
		size--;
	if (type & SPECIAL)
		if (base == 16)
			size -= 2;
		else if (base == 8)
			size--;
	i = 0;
	if (num == 0)
		tmp[i++] = '0';
	else while (num != 0)
		tmp[i++] = digits[do_div(num,base)];
	if (i > precision)
		precision = i;
	size -= precision;
	if (!(type & (ZEROPAD + LEFT)))
		while (size-- > 0)
			*str++ = ' ';
	if (sign)
		*str++ = sign;
	if (type & SPECIAL)
		if (base == 8) {
			*str++ = '0';
		} else if (base == 16) {
			*str++ = '0';
			*str++ = digits[33];
		}
	if (!(type & LEFT))
		while (size-- > 0)
			*str++ = c;
	while (i < precision--)
		*str++ = '0';
	while (i-- > 0)
		*str++ = tmp[i];
	while (size-- > 0)
		*str++ = ' ';
	return str;
}

/* Print formatted to a buffer */
int
vsprintf(char *buf, const char *fmt, va_list args)
{
	int len, i;
	char *str, *s;
	int *ip, flags;
	int field_width, precision, qualifier;

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

		/* Process flags */
		flags = 0;
repeat:
		fmt++;
		switch (*fmt) {
		case '-':
			flags |= LEFT;
			goto repeat;
		case '+':
			flags |= PLUS;
			goto repeat;
		case ' ':
			flags |= SPACE;
			goto repeat;
		case '#':
			flags |= SPECIAL;
			goto repeat;
		case '0':
			flags |= ZEROPAD;
			goto repeat;
		}

		/* Get field width */
		field_width = -1;
		if (is_digit(*fmt)) {
			field_width = skip_atoi(&fmt);
		} else if (*fmt == '*') {
			field_width = va_arg(args, int);
			fmt++;
			if (field_width < 0) {
				field_width = -field_width;
				flags |= LEFT;
			}
		}

		/* Get the precision */
		precision = -1;
		if (*fmt == '.') {
			fmt++;
			if (is_digit(*fmt)) {
				precision = skip_atoi(&fmt);
			} else if (*fmt == '*') {
				precision = va_arg(args, int);
				fmt++;
			}
			if (precision < 0)
				precision = 0;
		}

		/* Get the conversion qualifier */
		qualifier = -1;
		if (*fmt == 'h' || *fmt == 'l' || *fmt == 'L') {
			qualifier = *fmt;
			fmt++;
		}

		switch (*fmt) {
		case 'c':
			if (!(flags & LEFT))
				while (--field_width > 0)
					*str++ = ' ';
			*str++ = (unsigned char) va_arg(args, int);
			while (--field_width > 0)
				*str++ = ' ';
			break;

		case 's':
			s = va_arg(args, char *);
			len = strlen(s);
			if (precision < 0)
				precision = len;
			else if (len > precision)
				len = precision;

			if (!(flags & LEFT))
				while (len < field_width--)
					*str++ = ' ';
			for (i = 0; i < len; ++i)
				*str++ = *s++;
			while (len < field_width--)
				*str++ = ' ';
			break;

		case 'o':
			str = number(str, va_arg(args, unsigned long), 8,
				field_width, precision, flags);
			break;

		case 'p':
			if (field_width == -1) {
				field_width = 8;
				flags |= ZEROPAD;
			}
			str = number(str,
				(unsigned long) va_arg(args, void *), 16,
				field_width, precision, flags);
			break;

		case 'x':
			flags |= SMALL;
			/* FALLTHROUGH */
		case 'X':
			str = number(str, va_arg(args, unsigned long), 16,
				field_width, precision, flags);
			break;

		case 'd': /* FALLTHROUGH */
		case 'i':
			flags |= SIGN;
			/* FALLTHROUGH */
		case 'u':
			str = number(str, va_arg(args, unsigned long), 10,
				field_width, precision, flags);
			break;

		case 'f':
			str = number(str,
				(unsigned long) va_arg(args, double), 10,
				field_width, precision, flags);
			break;

		case 'n':
			ip = va_arg(args, int *);
			*ip = (str - buf);
			break;

		default:
			if (*fmt != '%')
				*str++ = '%';
			if (*fmt)
				*str++ = *fmt;
			else
				--fmt;
			break;
		}
	}
	*str = '\0';
	return str-buf;
}