1 files changed, 82 insertions, 0 deletions
diff --git a/interval.c b/interval.c
new file mode 100644
index 0000000..df9c14c
--- /dev/null
+++ b/interval.c
@@ -0,0 +1,82 @@
+/*
+ * for reference:
+ * - James F. Allen, Maintaining Knowledge about Temporal Intervals, CACM November 1983, Vol. 26, No. 11
+ * - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6188649/
+ */
+#include <u.h>
+#include <libc.h>
+#include "interval.h"
+
+static int
+interval_before(Interval *i, Interval *ii)
+{
+	return i->t1 < ii->t0;
+}
+
+static int
+interval_equals(Interval *i, Interval *ii)
+{
+	return i->t0 == ii->t0 &&
+		i->t1 == ii->t1;
+}
+
+static int
+interval_overlaps(Interval *i, Interval *ii)
+{
+	return i->t0 < ii->t0 &&
+		i->t1 > ii->t0 &&
+		i->t1 < ii->t1;
+}
+
+static int
+interval_meets(Interval *i, Interval *ii)
+{
+	return i->t1 == ii->t0;
+}
+
+static int
+interval_during(Interval *i, Interval *ii)
+{
+	return (i->t0 > ii->t0 && i->t1 <= ii->t1) ||
+		(i->t0 >= ii->t0 && i->t1 < ii->t1);
+}
+
+static int
+interval_intersects(Interval *i, Interval *ii)
+{
+	return i->equals(i, ii) ||
+		i->overlaps(i, ii) ||
+		ii->overlaps(ii, i) ||
+		i->during(i, ii) ||
+		ii->during(ii, i);
+}
+
+Interval *
+mkinterval(uvlong t0, uvlong t1)
+{
+	Interval *i;
+
+	assert(t0 <= t1);
+
+	i = malloc(sizeof(Interval));
+	if(i == nil)
+		sysfatal("mkinterval: %r");
+
+	i->t0 = t0;
+	i->t1 = t1;
+	i->∆t = t1-t0;
+	i->before = interval_before;
+	i->equals = interval_equals;
+	i->overlaps = interval_overlaps;
+	i->meets = interval_meets;
+	i->during = interval_during;
+	i->intersects = interval_intersects;
+
+	return i;
+}
+
+void
+rminterval(Interval *i)
+{
+	free(i);
+}