From a38695a71319db1cc2280b5270c925ee46c934f9 Mon Sep 17 00:00:00 2001
From: rodri <rgl@antares-labs.eu>
Date: Sat, 27 May 2023 01:58:37 +0000
Subject: initial release.

---
 interval.c | 82 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 interval.h | 16 ++++++++++++
 mkfile     |  7 ++++++
 readme.md  |  3 +++
 test.c     | 41 +++++++++++++++++++++++++++++++
 5 files changed, 149 insertions(+)
 create mode 100644 interval.c
 create mode 100644 interval.h
 create mode 100644 mkfile
 create mode 100644 readme.md
 create mode 100644 test.c

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);
+}
diff --git a/interval.h b/interval.h
new file mode 100644
index 0000000..e4a799e
--- /dev/null
+++ b/interval.h
@@ -0,0 +1,16 @@
+typedef struct Interval Interval;
+struct Interval
+{
+	uvlong t0, t1;
+	uvlong ∆t;	/* duration */
+
+	int (*before)(Interval*, Interval*);
+	int (*equals)(Interval*, Interval*);
+	int (*overlaps)(Interval*, Interval*);
+	int (*meets)(Interval*, Interval*);
+	int (*during)(Interval*, Interval*);
+	int (*intersects)(Interval*, Interval*);
+};
+
+Interval *mkinterval(uvlong, uvlong);
+void rminterval(Interval*);
diff --git a/mkfile b/mkfile
new file mode 100644
index 0000000..40c98dd
--- /dev/null
+++ b/mkfile
@@ -0,0 +1,7 @@
+</$objtype/mkfile
+
+LIB=libinterval.a$O
+OFILES=interval.$O
+HFILES=interval.h
+
+</sys/src/cmd/mklib
diff --git a/readme.md b/readme.md
new file mode 100644
index 0000000..df2e81b
--- /dev/null
+++ b/readme.md
@@ -0,0 +1,3 @@
+# libinterval
+
+Implementation of the ideas published in James F. Allen, Maintaining Knowledge about Temporal Intervals, CACM November 1983, Vol. 26, No. 11.
diff --git a/test.c b/test.c
new file mode 100644
index 0000000..2246330
--- /dev/null
+++ b/test.c
@@ -0,0 +1,41 @@
+#include <u.h>
+#include <libc.h>
+#include "interval.h"
+
+char *
+yn(int n)
+{
+	return n == 0? "no": "yes";
+}
+
+void
+usage(void)
+{
+	fprint(2, "usage: %s\n", argv0);
+	exits("usage");
+}
+
+void
+main(int argc, char *argv[])
+{
+	Interval *a, *b;
+
+	ARGBEGIN{
+	default: usage();
+	}ARGEND;
+	if(argc != 0)
+		usage();
+
+	a = mkinterval(20, 30);
+	b = mkinterval(25, 60);
+	print("a before b:\t%s\n", yn(a->before(a, b)));
+	print("a equals b:\t%s\n", yn(a->equals(a, b)));
+	print("a overlaps b:\t%s\n", yn(a->overlaps(a, b)));
+	print("a meets b:\t%s\n", yn(a->meets(a, b)));
+	print("a during b:\t%s\n", yn(a->during(a, b)));
+	print("a intersects b:\t%s\n", yn(a->intersects(a, b)));
+	rminterval(a);
+	rminterval(b);
+
+	exits(nil);
+}
-- 
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