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diff --git a/src/pkg/cmath/pow.go b/src/pkg/cmath/pow.go
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+// Copyright 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 cmath
+
+import "math"
+
+// The original C code, the long comment, and the constants
+// below are from http://netlib.sandia.gov/cephes/c9x-complex/clog.c.
+// The go code is a simplified version of the original C.
+//
+// Cephes Math Library Release 2.8:  June, 2000
+// Copyright 1984, 1987, 1989, 1992, 2000 by Stephen L. Moshier
+//
+// The readme file at http://netlib.sandia.gov/cephes/ says:
+//    Some software in this archive may be from the book _Methods and
+// Programs for Mathematical Functions_ (Prentice-Hall or Simon & Schuster
+// International, 1989) or from the Cephes Mathematical Library, a
+// commercial product. In either event, it is copyrighted by the author.
+// What you see here may be used freely but it comes with no support or
+// guarantee.
+//
+//   The two known misprints in the book are repaired here in the
+// source listings for the gamma function and the incomplete beta
+// integral.
+//
+//   Stephen L. Moshier
+//   moshier@na-net.ornl.gov
+
+// Complex power function
+//
+// DESCRIPTION:
+//
+// Raises complex A to the complex Zth power.
+// Definition is per AMS55 # 4.2.8,
+// analytically equivalent to cpow(a,z) = cexp(z clog(a)).
+//
+// ACCURACY:
+//
+//                      Relative error:
+// arithmetic   domain     # trials      peak         rms
+//    IEEE      -10,+10     30000       9.4e-15     1.5e-15
+
+// Pow returns x**y, the base-x exponential of y.
+func Pow(x, y complex128) complex128 {
+	modulus := Abs(x)
+	if modulus == 0 {
+		return complex(0, 0)
+	}
+	r := math.Pow(modulus, real(y))
+	arg := Phase(x)
+	theta := real(y) * arg
+	if imag(y) != 0 {
+		r *= math.Exp(-imag(y) * arg)
+		theta += imag(y) * math.Log(modulus)
+	}
+	s, c := math.Sincos(theta)
+	return complex(r*c, r*s)
+}