jens-maus/yam

/* asctime and asctime_r a la POSIX and ISO C, except pad years before 1000.  */

/*
** This file is in the public domain, so clarified as of
** 1996-06-05 by Arthur David Olson.
*/

/*
** Avoid the temptation to punt entirely to strftime;
** the output of strftime is supposed to be locale specific
** whereas the output of asctime is supposed to be constant.
*/

/*LINTLIBRARY*/

#include "private.h"
#include <stdio.h>

/*
** Some systems only handle "%.2d"; others only handle "%02d";
** "%02.2d" makes (most) everybody happy.
** At least some versions of gcc warn about the %02.2d;
** we conditionalize below to avoid the warning.
*/
/*
** All years associated with 32-bit time_t values are exactly four digits long;
** some years associated with 64-bit time_t values are not.
** Vintage programs are coded for years that are always four digits long
** and may assume that the newline always lands in the same place.
** For years that are less than four digits, we pad the output with
** leading zeroes to get the newline in the traditional place.
** The -4 ensures that we get four characters of output even if
** we call a strftime variant that produces fewer characters for some years.
** The ISO C and POSIX standards prohibit padding the year,
** but many implementations pad anyway; most likely the standards are buggy.
*/
#ifdef __GNUC__
#define ASCTIME_FMT    "%s %s%3d %2.2d:%2.2d:%2.2d %-4s\n"
#else /* !defined __GNUC__ */
#define ASCTIME_FMT    "%s %s%3d %02.2d:%02.2d:%02.2d %-4s\n"
#endif /* !defined __GNUC__ */
/*
** For years that are more than four digits we put extra spaces before the year
** so that code trying to overwrite the newline won't end up overwriting
** a digit within a year and truncating the year (operating on the assumption
** that no output is better than wrong output).
*/
#ifdef __GNUC__
#define ASCTIME_FMT_B    "%s %s%3d %2.2d:%2.2d:%2.2d     %s\n"
#else /* !defined __GNUC__ */
#define ASCTIME_FMT_B    "%s %s%3d %02.2d:%02.2d:%02.2d     %s\n"
#endif /* !defined __GNUC__ */

#define STD_ASCTIME_BUF_SIZE    26
/*
** Big enough for something such as
** ??? ???-2147483648 -2147483648:-2147483648:-2147483648     -2147483648\n
** (two three-character abbreviations, five strings denoting integers,
** seven explicit spaces, two explicit colons, a newline,
** and a trailing NUL byte).
** The values above are for systems where an int is 32 bits and are provided
** as an example; the define below calculates the maximum for the system at
** hand.
*/
#define MAX_ASCTIME_BUF_SIZE    (2*3+5*INT_STRLEN_MAXIMUM(int)+7+2+1+1)

static char    buf_asctime[MAX_ASCTIME_BUF_SIZE];

char *
asctime_r(register const struct tm *timeptr, char *buf)
{
    static const char    wday_name[][4] = {
        "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
    };
    static const char    mon_name[][4] = {
        "Jan", "Feb", "Mar", "Apr", "May", "Jun",
        "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
    };
    register const char *    wn;
    register const char *    mn;
    char            year[INT_STRLEN_MAXIMUM(int) + 2];
    char            result[MAX_ASCTIME_BUF_SIZE];

    if (timeptr == NULL) {
        errno = EINVAL;
        return strcpy(buf, "??? ??? ?? ??:??:?? ????\n");
    }
    if (timeptr->tm_wday < 0 || timeptr->tm_wday >= DAYSPERWEEK)
        wn = "???";
    else    wn = wday_name[timeptr->tm_wday];
    if (timeptr->tm_mon < 0 || timeptr->tm_mon >= MONSPERYEAR)
        mn = "???";
    else    mn = mon_name[timeptr->tm_mon];
    /*
    ** Use strftime's %Y to generate the year, to avoid overflow problems
    ** when computing timeptr->tm_year + TM_YEAR_BASE.
    ** Assume that strftime is unaffected by other out-of-range members
    ** (e.g., timeptr->tm_mday) when processing "%Y".
    */
    strftime(year, sizeof year, "%Y", timeptr);
    /*
    ** We avoid using snprintf since it's not available on all systems.
    */
    sprintf(result,
        ((strlen(year) <= 4) ? ASCTIME_FMT : ASCTIME_FMT_B),
        wn, mn,
        timeptr->tm_mday, timeptr->tm_hour,
        timeptr->tm_min, timeptr->tm_sec,
        year);
    if (strlen(result) < STD_ASCTIME_BUF_SIZE || buf == buf_asctime)
        return strcpy(buf, result);
    else {
        errno = EOVERFLOW;
        return NULL;
    }
}

char *
asctime(register const struct tm *timeptr)
{
    return asctime_r(timeptr, buf_asctime);
}