source: buchla-68k/orig/DATE/CALNDR.C@ d21fc6f

/*
   =============================================================================
        calndr.c -- print a calendar
        Version 1 -- 1986-10-06
   =============================================================================
*/

#include <time.h>

char    dayw[] = {
        " S  M Tu  W Th  F  S"
};

char    *smon[]= {
        "January", "February", "March", "April",
        "May", "June", "July", "August",
        "September", "October", "November", "December",
};

char    mon[] = {
        0,
        31, 29, 31, 30,
        31, 30, 31, 31,
        30, 31, 30, 31,
};


char    string[432];

extern struct tm *localtime();
extern long time();

struct tm *thetime;
long timbuf;

/*
   =============================================================================
        main function for calndr command
   =============================================================================
*/

main(argc, argv)
char *argv[];
{
        register y, i, j;
        int m;

        switch(argc) {

        case 1:
                timbuf = time(&timbuf);
                thetime = localtime(&timbuf);
                m = thetime->tm_mon + 1;
                y = thetime->tm_year + 1900;
                break;

        case 2:
                goto xlong;

        case 3:
                m = number(argv[1]);
                y = number(argv[2]);
                break;

        default:
                printf("usage: calndr [ [month] year ]\n");
                exit(0);
        }

        /* print out just month */

        if(m<1 || m>12)
                goto badarg;

        if(y<1 || y>9999)
                goto badarg;

        printf("   %s %u\n\n", smon[m-1], y);
        printf("%s\n", dayw);

        cal(m, y, string, 24);

        for(i=0; i<6*24; i+=24)
                pstr(string+i, 24);

        exit(0);

        /* print out complete year */

xlong:
        y = number(argv[1]);

        if(y<1 || y>9999)
                goto badarg;

        printf("\n\n\n");
        printf("                                %u\n", y);
        printf("\n");

        for(i=0; i<12; i+=3) {

                for(j=0; j<6*72; j++)
                        string[j] = '\0';

                printf("         %.3s", smon[i]);
                printf("                        %.3s", smon[i+1]);
                printf("                       %.3s\n", smon[i+2]);
                printf("%s   %s   %s\n", dayw, dayw, dayw);

                cal(i+1, y, string, 72);
                cal(i+2, y, string+23, 72);
                cal(i+3, y, string+46, 72);

                for(j=0; j<6*72; j+=72)
                        pstr(string+j, 72);
        }

        printf("\n\n\n");
        exit(0);

badarg:
        printf("calndr:  Bad argument\n");
        exit(1);
}

/*
   =============================================================================
        number(str) -- extract an integer from str
   =============================================================================
*/

number(str)
char *str;
{
        register n, c;
        register char *s;

        n = 0;
        s = str;

        while(c = *s++) {

                if(c<'0' || c>'9')
                        return(0);

                n = n*10 + c-'0';
        }

        return(n);
}

/*
   =============================================================================
        pstr(str, n)
   =============================================================================
*/

pstr(str, n)
char *str;
{
        register i;
        register char *s;

        s = str;
        i = n;

        while(i--)
                if(*s++ == '\0')
                        s[-1] = ' ';

        i = n+1;

        while(i--)
                if(*--s != ' ')
                        break;

        s[1] = '\0';
        printf("%s\n", str);
}

/*
   =============================================================================
        cal(m, y, p, w) -- calculate calendar string
   =============================================================================
*/

cal(m, y, p, w)
char *p;
{
        register d, i;
        register char *s;

        s = p;
        d = jan1(y);
        mon[2] = 29;
        mon[9] = 30;

        switch((jan1(y+1)+7-d)%7) {

        /*
         *      non-leap year
         */
        case 1:
                mon[2] = 28;
                break;

        /*
         *      1752
         */
        default:
                mon[9] = 19;
                break;

        /*
         *      leap year
         */
        case 2:
                ;
        }

        for(i=1; i<m; i++)
                d += mon[i];

        d %= 7;
        s += 3*d;

        for(i=1; i<=mon[m]; i++) {

                if(i==3 && mon[m]==19) {
                        i += 11;
                        mon[m] += 11;
                }

                if(i > 9)
                        *s = i/10+'0';

                s++;
                *s++ = i%10+'0';
                s++;

                if(++d == 7) {
                        d = 0;
                        s = p+w;
                        p = s;
                }
        }
}

/*
   =============================================================================
        jan1(yr) -- return day of the week
        of jan 1 of given year
   =============================================================================
 */

jan1(yr)
{
        register y, d;

        /* normal gregorian calendar -- one extra day per four years */

        y = yr;
        d = 4+y+(y+3)/4;

        /* julian calendar -- regular gregorian less three days per 400 */

        if(y > 1800) {
                d -= (y-1701)/100;
                d += (y-1601)/400;
        }

        /* great calendar changeover instant */

        if(y > 1752)
                d += 3;

        return(d%7);
}