| 1 | #include <stdio.h> |
| 2 | |
| 3 | char *computus(int year, int servois, char *out, size_t out_size) { |
| 4 | // Year's position on the 19 year metonic cycle |
| 5 | int a = year % 19; |
| 6 | |
| 7 | // Century index |
| 8 | int k = year / 100; |
| 9 | |
| 10 | //Shift of metonic cycle, add a day offset every 300 years |
| 11 | int p = (13 + 8 * k) / 25; |
| 12 | |
| 13 | // Correction for non-observed leap days |
| 14 | int q = k / 4; |
| 15 | |
| 16 | // Correction to starting point of calculation each century |
| 17 | int M = (15 - p + k - q) % 30; |
| 18 | |
| 19 | // Number of days from March 21st until the full moon |
| 20 | int d = (19 * a + M) % 30; |
| 21 | |
| 22 | // Returning if user wants value for Servois' table |
| 23 | if (servois) { |
| 24 | snprintf(out, out_size, "%d",(21 + d) % 31); |
| 25 | return out; |
| 26 | } |
| 27 | |
| 28 | // Finding the next Sunday |
| 29 | // Century-based offset in weekly calculation |
| 30 | int N = (4 + k - q) % 7; |
| 31 | |
| 32 | // Correction for leap days |
| 33 | int b = year % 4; |
| 34 | int c = year % 7; |
| 35 | |
| 36 | // Days from d to next Sunday |
| 37 | int e = (2 * b + 4 * c + 6 * d + N) % 7; |
| 38 | |
| 39 | // Historical corrections for April 26 and 25 |
| 40 | if ((d == 29 && e == 6) || (d == 28 && e == 6 && a > 10)) { |
| 41 | e = -1; |
| 42 | } |
| 43 | |
| 44 | if ((22 + d + e) > 31) { |
| 45 | snprintf(out, out_size, "April %d", d + e - 9); |
| 46 | } else { |
| 47 | snprintf(out, out_size, "March %d", 22 + d + e); |
| 48 | } |
| 49 | |
| 50 | return out; |
| 51 | } |
| 52 | |
| 53 | int main() { |
| 54 | char tmp1[9], tmp2[9]; |