1 files changed, 49 insertions, 0 deletions
diff --git a/src/pkg/math/hypot.go b/src/pkg/math/hypot.go
new file mode 100644
index 000000000..411f74e4f
--- /dev/null
+++ b/src/pkg/math/hypot.go
@@ -0,0 +1,49 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package math
+
+/*
+ *	hypot -- sqrt(p*p + q*q), but overflows only if the result does.
+ *	See Cleve Moler and Donald Morrison,
+ *	Replacing Square Roots by Pythagorean Sums
+ *	IBM Journal of Research and Development,
+ *	Vol. 27, Number 6, pp. 577-581, Nov. 1983
+ */
+
+// Hypot computes Sqrt(p*p + q*q), taking care to avoid
+// unnecessary overflow and underflow.
+func Hypot(p, q float64) float64 {
+	if p < 0 {
+		p = -p;
+	}
+	if q < 0 {
+		q = -q;
+	}
+
+	if p < q {
+		p, q = q, p;
+	}
+
+	if p == 0 {
+		return 0;
+	}
+
+	pfac := p;
+	q = q/p;
+	r := q;
+	p = 1;
+	for {
+		r = r*r;
+		s := r+4;
+		if s == 4 {
+			return p*pfac;
+		}
+		r = r/s;
+		p = p + 2*r*p;
+		q = q*r;
+		r = q/p;
+	}
+	panic("unreachable")
+}