vsprintf.c

一个用于学习的操作系统

/*
 *  linux/kernel/vsprintf.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

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

#include <stdarg.h>
#include <fairysky/types.h>
#include <fairysky/string.h>

/* 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' */

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

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 */
            ++fmt;
            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;
}