From 11da511c784eca003deb90c23570f0873954e0de Mon Sep 17 00:00:00 2001
From: Duncan Wilkie <antigravityd@gmail.com>
Date: Sat, 18 Nov 2023 06:11:09 -0600
Subject: Initial commit.

---
 ic-reals-6.3/base/strategy.c | 87 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 87 insertions(+)
 create mode 100644 ic-reals-6.3/base/strategy.c

(limited to 'ic-reals-6.3/base/strategy.c')

diff --git a/ic-reals-6.3/base/strategy.c b/ic-reals-6.3/base/strategy.c
new file mode 100644
index 0000000..d1c8e35
--- /dev/null
+++ b/ic-reals-6.3/base/strategy.c
@@ -0,0 +1,87 @@
+/*
+ * Copyright (C) 2000, Imperial College
+ *
+ * This file is part of the Imperial College Exact Real Arithmetic Library.
+ * See the copyright notice included in the distribution for conditions
+ * of use.
+ */
+
+#include <stdio.h>
+#include "real.h"
+#include "real-impl.h"
+
+/*
+ * Functions related to ``information overlap'' tensor strategy. Can
+ * probably be dropped and reky soley on epsilon-delta stuff.
+ */
+static mpz_t a_times_d, c_times_b;
+
+void
+initStrategy()
+{
+	mpz_init(a_times_d);
+	mpz_init(c_times_b);
+}
+
+/*
+ * Given vectors (a,b) and (c,d), this returns
+ *  -1 if (a,b) < (c,d)
+ *  =0 if (a,b) = (c,d)
+ *  +1 if (a,b) > (c,d)
+ */
+static int
+compareVectors(Vector v0, Vector v1)
+{
+	int tmp;
+
+	mpz_mul(a_times_d, v0[0], v1[1]);
+	mpz_mul(c_times_b, v1[0], v0[1]);
+	tmp = mpz_cmp(a_times_d, c_times_b);
+	return MPZ_SIGN(tmp);
+}
+
+/*
+ * This is Peter's ``information overlap'' strategy. 
+ *
+ * If the structure of the code seems odd, it is because we want to avoid
+ * doing the same operations more than once. C guarantees that when evaluating
+ * a conjunction, if the first conjunct is false, then the second is
+ * not evaluated.
+ *
+ * This returns 1 to select y (right) and 0 to select x (left).
+ */
+int
+tensorStrategy(Tensor t)
+{
+	int v0cv1;
+
+	/*
+	 * we compare:
+	 *  v0 <> v1
+	 *  v0 <> v3
+	 *  v2 <> v1
+	 *  v2 <> v3
+	 */
+	v0cv1 = compareVectors(t[0], t[1]);
+	if (v0cv1 > 0) {
+		if ((compareVectors(t[0], t[3]) > 0)
+			&& (compareVectors(t[2], t[1]) > 0)
+			&& (compareVectors(t[2], t[3]) > 0)) {
+			return 1;
+		}
+		else
+			return 0;
+	}
+	else {
+		if (v0cv1 < 0) {
+			if ((compareVectors(t[0], t[3]) < 0)
+				&& (compareVectors(t[2], t[1]) < 0)
+				&& (compareVectors(t[2], t[3]) < 0)) {
+				return 1;
+			}
+			else
+				return 0;
+		}
+	}
+	return 0;
+}
-- 
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