printf.c

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/*
 *  The contents of this file are subject to the Mozilla Public License
 *  Version 1.0 (the "License"); you may not use this file except in
 *  compliance with the License. You may obtain a copy of the License at
 *  http://www.mozilla.org/MPL/
 *
 *  Software distributed under the License is distributed on an "AS IS"
 *  basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the
 *  License for the specific language governing rights and limitations
 *  under the License.
 *
 *  The Original Code is from the Brown Computer Science Department,
 *  Weenix support code.
 *
 *  The Initial Developer of the Original Code is David Powell.
 *
 *  Contributor(s): Matthew Ahrens <mahrens@acm.org>
 */

#include <stdarg.h>

static const char hexdigits[] = "0123456789ABCDEF";
static const char lhexdigits[] = "0123456789abcdef";
static const char empty_string[] = "(null string)";

/* This function takes an unsigned int and puts its ascii
 * representation at a particular location in a buffer of given
 * length.  The radix used is must also be provided, as well as a
 * string containing the characters used in the ascii representation.
 *
 * This function makes no attempt to handle two-byte characters. 
 */
static int itoa(unsigned int value, char *dst, int pos, int len,
                int radix, const char *digits)
{
        char    sbuf[10];
        int     spos;

        spos = 0;
        while(value) {
                sbuf[spos] = value % radix;
                spos++;
                value /= radix;
        }
        if(!spos)
                *sbuf = 0, spos = 1;

        for(spos--; pos<len && spos>=0; pos++,spos--) {
                dst[pos] = digits[(int)sbuf[spos]];
        }

        return pos-1;
}


/* This function takes a buffer, its length, a format specification,
 * and a va_list, formats the provided data according the the format
 * spec, and places the result in the buffer.  It returns the length of
 * the output.  The only format options supported by this function
 * are:
 *   %d - decimal unsigned int
 *   %i -    "        "     "
 *   %x - hexidecimal unsigned int (lowercase letters)
 *   %X -      "          "     "   (uppercase letters)
 *   %c - character
 *   %s - string
 *   %% - '%' character
 */
int vsnprintf(char *dst, int len, const char *fmt, va_list arg)
{
        int             pos;
        int             cc;
        const char      *temp;
        unsigned int    scratch;

        for(pos=0, cc=0; (pos<len) && (cc=*fmt); pos++, fmt++) {
                if(cc!='%')
                        dst[pos] = cc;
                else {
                        cc = *(++fmt);
                        switch(cc) {
                        case 'd':
                        case 'i':
                                /* integer */
                                scratch = va_arg(arg, unsigned);
                                pos = itoa(scratch, dst, pos, len, 10,
                                           hexdigits);
                                break;
                        case 'X':
                                /* hexadecimal (uppercase) */
                                scratch = va_arg(arg, unsigned);
                                pos = itoa(scratch, dst, pos, len, 16,
                                           hexdigits);
                                break;
                        case 'x':
                                /* hexadecimal (lowercase) */
                                scratch = va_arg(arg, unsigned);
                                pos = itoa(scratch, dst, pos, len, 16,
                                           lhexdigits);
                                break;
                        case 's':
                                /* string */
                                temp = va_arg(arg, const char*);
                                if(!temp)
                                        temp = empty_string;
                                for(; pos<len && *temp; pos++, temp++) {
                                        dst[pos] = *temp;
                                }
                                pos--;
                                break;
                        case 'c':
                                /* character */
                                dst[pos] = va_arg(arg, int);
                                break;
                        case '\0':
                        case '%':
                                dst[pos] = cc;
                                break;
                        }

                        if(!cc) {
                                break;
                        }
                }
        }

        dst[pos++] = '\0';

        return pos;
}


/* This function prints the specified format into the provided buffer
 * taking care not to access beyond the end of the string. 
 */
char *snprintf(char *dst, int len, const char *fmt, ...)
{
        va_list arg;

        va_start(arg, fmt);
        (void) vsnprintf(dst, len, fmt, arg);
        va_end(arg);

        return dst;
}

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