Add ISO-8601 calendar conversion functions

src/lib/calendar_iso8601.rs

@@ -0,0 +1,123 @@
+static EPOCH_LEN: int = 146097;
+static MONTHDAY: [int, ..12] = [
+    0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334
+];
+
+/// Convert an ISO 8601 date to a chronological Julian day.
+pub fn to_cjd(year: int, month: int, day: int) -> int {
+    let y = year - 2000;
+    let mut a = y % 400;
+    let mut b = y / 400;
+    if a < 0 {
+        a += 400;
+        b -= 1;
+    }
+    let mut leap = 1 + a / 4 - a / 100;
+    if month <= 2 && (a % 4) == 0 && ((a % 100) != 0 || a == 0) {
+        leap -= 1;
+    }
+    146097 * b + 365 * a + MONTHDAY[(month - 1) as uint] + day - 1 + leap
+}
+
+/// Convert a chronological Julian day to an ISO 8601 date.
+pub fn from_cjd(cjd: int) -> (int, int, int) {
+    let mut t1 = cjd / EPOCH_LEN;
+    let mut d = cjd % EPOCH_LEN;
+    if d < 0 {
+        t1 -= 1;
+        d += EPOCH_LEN;
+    }
+    let y = t1 * 400 + 2000;
+
+    let t2 = (d - 1) / 36524;
+    let d = (d - 1) % 36524;
+    let y = y + t2 * 100;
+
+    let t3 = (d + 1) / 1461;
+    let d = (d + 1) % 1461;
+    let y = y + t3 * 4;
+
+    let t4 = (d - 1) / 365;
+    let d = (d - 1) % 365;
+    let y = y + t4;
+
+    let mut m = d / 29 + 1;
+    if m > 12 || (m > 1 && d < MONTHDAY[(m - 1) as uint]) {
+        m -= 1;
+    }
+
+    let mut d = d - MONTHDAY[(m - 1) as uint] + 1;
+    if t4 == 0 && (t3 != 0 || t2 == 0) && m <= 2 {
+        d += 1;
+        if d == 32 {
+            m = 2;
+            d = 1;
+        }
+    }
+
+    (y, m, d)
+}
+
+#[test]
+fn cjd_point() {
+    fn test(cjd: int, y: int, m: int, d: int) {
+        let out_cjd = to_cjd(y, m, d);
+        if out_cjd != cjd {
+            fail!("{:04d}-{:02d}-{:02d}: expected {}, got {}",
+                  y, m, d, cjd, out_cjd);
+        }
+
+        let (y2, m2, d2) = from_cjd(cjd);
+        if y != y2 || m != m2 || d != d2 {
+            fail!("{}: expected {:04d}-{:02d}-{:02d}, got {:04d}-{:02d}-{:02d}",
+                  cjd, y, m, d, y2, m2, d2);
+        }
+    }
+
+    test(0, 2000, 1, 1);
+    test(1, 2000, 1, 2);
+    test(-1, 1999, 12, 31);
+    test(146097, 2400, 1, 1);
+    test(-146097, 1600, 1, 1);
+}
+
+#[test]
+fn cjd_range() {
+    static MONTHS: [int, ..12] = [
+        31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
+    ];
+
+    fn test_range(start: int, end: int) {
+        let mut y = start;
+        let mut m = 1;
+        let mut d = 1;
+        let mut last_cjd = to_cjd(y, m, d) - 1;
+        while y < end {
+            let cjd = to_cjd(y, m, d);
+            if cjd != last_cjd + 1 {
+                fail!("Nonconsecutive date.");
+            }
+            last_cjd = cjd;
+            let (y2, m2, d2) = from_cjd(cjd);
+            if y != y2 || m != m2 || d != d2 {
+                fail!("Bad conversion: {:04d}-{:02d}-{:02d} to {} to {:04d}-{:02d}-{:02d}",
+                      y, m, d, cjd, y2, m2, d2);
+            }
+            d += 1;
+            if d > MONTHS[(m - 1) as uint] {
+                let is_leap = m == 2 && d == 29 && (y % 4) == 0 &&
+                              ((y % 100) != 0 || (y % 400) == 0);
+                if !is_leap {
+                    m += 1;
+                    d = 1;
+                    if m >= 13 {
+                        m = 1;
+                        y += 1;
+                    }
+                }
+            }
+        }
+    }
+
+    test_range(1596, 2404);
+}