repos / gbc

cal3.bx

 1extrn printf, time, localtime;
 2
 3/*
 4 * On amd64_sysv, the C struct tm has the following layout:
 5 *
 6 * struct tm {
 7 * int tm_sec;    // 0
 8 * int tm_min;    // 4
 9 * int tm_hour;   // 8
10 * int tm_mday;   // 12
11 * int tm_mon;    // 16
12 * int tm_year;   // 20
13 * int tm_wday;   // 24
14 * int tm_yday;   // 28
15 * int tm_isdst;  // 32
16 * };
17 *
18 * All members are 4-byte integers.
19 */
20
21int days_in_month(m int, y int) {
22    if (m == 1) { // February
23        if ((y % 400 == 0) | ((y % 4 == 0) & (y % 100 != 0))) {
24            return (29);
25        } else {
26            return (28);
27        };
28    };
29    if ((m == 0) | (m == 2) | (m == 4) | (m == 6) | (m == 7) | (m == 9) | (m == 11)) {
30        return (31);
31    };
32    return (30);
33}
34
35int main() {
36    now := time(0);
37    tptr := localtime(&now);
38
39    byte_ptr := (*byte)tptr;
40    year  := *((*int)(byte_ptr + 20)) + 1900;
41    month := *((*int)(byte_ptr + 16));    // 0 = Jan
42    today := *((*int)(byte_ptr + 12));
43    wday  := *((*int)(byte_ptr + 24));
44
45    days := days_in_month(month, year);
46
47    printf("    %d/%d\n", month + 1, year);
48    printf("Su Mo Tu We Th Fr Sa\n");
49
50    // Calculate the weekday of the first day of the month.
51    // wday is for today, so we go back (today - 1) days.
52    // The result must be non-negative, so we add 7 before the modulo
53    first_wday := (wday - (today - 1) % 7 + 7) % 7;
54
55    i := 0;
56    while (i < first_wday) {
57        printf("   ");
58        i = i + 1;
59    };
60
61    d := 1;
62    while (d <= days) {
63        if (d == today) {
64            printf("\033[31m%2d\033[0m ", d);
65        } else {
66            printf("%2d ", d);
67        };
68
69        current_wday := (first_wday + d - 1) % 7;
70        if (current_wday == 6) { // It's Saturday, add \n
71            printf("\n");
72        };
73        d = d + 1;
74    };
75    printf("\n");
76    return (0);
77}