sprintf 与printf 源码分析

/* -*- linux-c -*- ------------------------------------------------------- *
 *
 * Copyright (C) 1991, 1992 Linus Torvalds
 * Copyright 2007 rPath, Inc. - All Rights Reserved
 *
 * This file is part of the Linux kernel, and is made available under
 * the terms of the GNU General Public License version 2.
 *
 * ----------------------------------------------------------------------- */

/*
 * Oh, it's a waste of space, but oh-so-yummy for debugging. This
 * version of printf() does not include 64-bit support. "Live with
 * it."
 *
 */

#include "boot.h"

static int skip_atoi(const char **s)
{
    int i = 0;

    while (isdigit(**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 SMALL    32        /* Must be 32 == 0x20 */
#define SPECIAL    64        /* 0x */

#define __do_div(n, base) ({ \
int __res; \
__res = ((unsigned long) n) % (unsigned) base; \
n = ((unsigned long) n) / (unsigned) base; \
__res; })

static char *number(char *str, long num, int base, int size, int precision,
         int type)
{
    /* we are called with base 8, 10 or 16, only, thus don't need "G..." */
    static const char digits[16] = "0123456789ABCDEF"; /* "GHIJKLMNOPQRSTUVWXYZ"; */

    char tmp[66];
    char c, sign, locase;
    int i;

    /* locase = 0 or 0x20. ORing digits or letters with 'locase'
     * produces same digits or (maybe lowercased) letters */
    locase = (type & SMALL);
    if (type & LEFT)
        type &= ~ZEROPAD;
    if (base < 2 || base > 36)
        return NULL;
    c = (type & ZEROPAD) ? '0' : ' ';
    sign = 0;
    if (type & SIGN) {
        if (num < 0) {
            sign = '-';
            num = -num;
            size--;
        } else if (type & PLUS) {
            sign = '+';
            size--;
        } else if (type & SPACE) {
            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)] | locase);
    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++ = ('X' | locase);
        }
    }
    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;
    unsigned long num;
    int i, base;
    char *str;
    const char *s;

    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 (isdigit(*fmt))
            field_width = skip_atoi(&fmt);
        else if (*fmt == '*') {
            ++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 (isdigit(*fmt))
                precision = skip_atoi(&fmt);
            else if (*fmt == '*') {
                ++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;
        }

        /* default base */
        base = 10;

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

        case 's':
            s = va_arg(args, char *);
            len = strnlen(s, precision);

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

        case 'p':
            if (field_width == -1) {
                field_width = 2 * sizeof(void *);
                flags |= ZEROPAD;
            }
            str = number(str,
                 (unsigned long)va_arg(args, void *), 16,
                 field_width, precision, flags);
            continue;

        case 'n':
            if (qualifier == 'l') {
                long *ip = va_arg(args, long *);
                *ip = (str - buf);
            } else {
                int *ip = va_arg(args, int *);
                *ip = (str - buf);
            }
            continue;

        case '%':
            *str++ = '%';
            continue;

            /* integer number formats - set up the flags and "break" */
        case 'o':
            base = 8;
            break;

        case 'x':
            flags |= SMALL;
        case 'X':
            base = 16;
            break;

        case 'd':
        case 'i':
            flags |= SIGN;
        case 'u':
            break;

        default:
            *str++ = '%';
            if (*fmt)
                *str++ = *fmt;
            else
                --fmt;
            continue;
        }
        if (qualifier == 'l')
            num = va_arg(args, unsigned long);
        else if (qualifier == 'h') {
            num = (unsigned short)va_arg(args, int);
            if (flags & SIGN)
                num = (short)num;
        } else if (flags & SIGN)
            num = va_arg(args, int);
        else
            num = va_arg(args, unsigned int);
        str = number(str, num, base, field_width, precision, flags);
    }
    *str = '\0';
    return str - buf;
}

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;
}

int printf(const char *fmt, ...)
{
    char printf_buf[1024];
    va_list args;
    int printed;

    va_start(args, fmt);
    printed = vsprintf(printf_buf, fmt, args);
    va_end(args);

    puts(printf_buf);

    return printed;
}