l_stdio.cpp

一本叫自己动手写嵌入式操作系统的书的源代码,作者是蓝枫叶,详细介绍了如何写一个嵌入式操作系统,而不是操作系统

#include "..\INCLUDE\L_STDIO.H"

/*
 *  linux/kernel/vsprintf.c
 *
 *  (C) 1991  Linus Torvalds
 */

/* vsprintf.c -- Lars Wirzenius & Linus Torvalds. */
/*
 * Wirzenius wrote this portably, Torvalds fucked it up :-)
 */

static int strlen(const char* s)
{
	int len = -1;
	while(s[++ len]);
	return len;
}

/* we use this so that we can do without the ctype library */
#define is_digit(c)     ((c) >= '0' && (c) <= '9')

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' */

static int getdig(int* n,int base)
{
	/*int max = base;
	int num = *n;

	while(max < num)
	{
		max *= base;
	}
	max /= base;

	if(*n > max)
	{
		*n = *n % max;
	}
	else
	{
		*n = 0;
	}
	return num / max;*/

	int ret = *n % base;
	*n = (*n) / base;
	return ret;
}

#define do_div(n,base) (getdig(&n,base))

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;
}

int vsprintf(char *buf, const char *fmt, va_list args)
{
        int len;
        int i;
        char * str;
        char *s;
        int *ip;

        int flags;              /* flags to number() */

        int field_width;        /* width of output field */
        int precision;          /* min. # of digits for integers; max
                                   number of chars for from string */
        int qualifier;          /* 'h', 'l', or 'L' for integer fields */

        for (str=buf ; *fmt ; ++fmt) {
                if (*fmt != '%') {
                        *str++ = *fmt;
                        continue;
                }
                        
                /* process flags */
                flags = 0;
                repeat:
                        ++fmt;          /* this also skips first '%' */
                        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 == '*') {
                        /* it's the next argument */
                        field_width = va_arg(args, int);
                        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 == '*') {
                                /* it's the next argument */
                                precision = va_arg(args, int);
                        }
                        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;
                case 'X':
                        str = number(str, va_arg(args, unsigned long), 16,
                                field_width, precision, flags);
                        break;

                case 'd':
                case 'i':
                        flags |= SIGN;
                case 'u':
                        str = number(str, va_arg(args, unsigned long), 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;
}
/**
 * sprintf - Format a string and place it in a buffer
 * @buf: The buffer to place the result into
 * @fmt: The format string to use
 * @...: Arguments for the format string
 */
int sprintf(char * buf, const char *fmt, ...)
{
        va_list args;
        int i;

        va_start(args, fmt);
        i=vsprintf(buf,fmt,args);
        va_end(args);
        return i;
}