1 files changed, 47 insertions, 0 deletions
diff --git a/libgo/go/math/mod.go b/libgo/go/math/mod.go
new file mode 100644
index 00000000000..6b16abe5d13
--- /dev/null
+++ b/libgo/go/math/mod.go
@@ -0,0 +1,47 @@
+// Copyright 2009-2010 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
+
+/*
+	Floating-point mod function.
+*/
+
+// Mod returns the floating-point remainder of x/y.
+// The magnitude of the result is less than y and its
+// sign agrees with that of x.
+//
+// Special cases are:
+//	if x is not finite, Mod returns NaN
+//	if y is 0 or NaN, Mod returns NaN
+func Mod(x, y float64) float64 {
+	// TODO(rsc): Remove manual inlining of IsNaN, IsInf
+	// when compiler does it for us.
+	if y == 0 || x > MaxFloat64 || x < -MaxFloat64 || x != x || y != y { // y == 0 || IsInf(x, 0) || IsNaN(x) || IsNan(y)
+		return NaN()
+	}
+	if y < 0 {
+		y = -y
+	}
+
+	yfr, yexp := Frexp(y)
+	sign := false
+	r := x
+	if x < 0 {
+		r = -x
+		sign = true
+	}
+
+	for r >= y {
+		rfr, rexp := Frexp(r)
+		if rfr < yfr {
+			rexp = rexp - 1
+		}
+		r = r - Ldexp(y, rexp-yexp)
+	}
+	if sign {
+		r = -r
+	}
+	return r
+}