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diff --git a/src/math/cmplx/sin.go b/src/math/cmplx/sin.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 cmplx
+
+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 circular sine
+//
+// DESCRIPTION:
+//
+// If
+//     z = x + iy,
+//
+// then
+//
+//     w = sin x  cosh y  +  i cos x sinh y.
+//
+// csin(z) = -i csinh(iz).
+//
+// ACCURACY:
+//
+//                      Relative error:
+// arithmetic   domain     # trials      peak         rms
+//    DEC       -10,+10      8400       5.3e-17     1.3e-17
+//    IEEE      -10,+10     30000       3.8e-16     1.0e-16
+// Also tested by csin(casin(z)) = z.
+
+// Sin returns the sine of x.
+func Sin(x complex128) complex128 {
+	s, c := math.Sincos(real(x))
+	sh, ch := sinhcosh(imag(x))
+	return complex(s*ch, c*sh)
+}
+
+// Complex hyperbolic sine
+//
+// DESCRIPTION:
+//
+// csinh z = (cexp(z) - cexp(-z))/2
+//         = sinh x * cos y  +  i cosh x * sin y .
+//
+// ACCURACY:
+//
+//                      Relative error:
+// arithmetic   domain     # trials      peak         rms
+//    IEEE      -10,+10     30000       3.1e-16     8.2e-17
+
+// Sinh returns the hyperbolic sine of x.
+func Sinh(x complex128) complex128 {
+	s, c := math.Sincos(imag(x))
+	sh, ch := sinhcosh(real(x))
+	return complex(c*sh, s*ch)
+}
+
+// Complex circular cosine
+//
+// DESCRIPTION:
+//
+// If
+//     z = x + iy,
+//
+// then
+//
+//     w = cos x  cosh y  -  i sin x sinh y.
+//
+// ACCURACY:
+//
+//                      Relative error:
+// arithmetic   domain     # trials      peak         rms
+//    DEC       -10,+10      8400       4.5e-17     1.3e-17
+//    IEEE      -10,+10     30000       3.8e-16     1.0e-16
+
+// Cos returns the cosine of x.
+func Cos(x complex128) complex128 {
+	s, c := math.Sincos(real(x))
+	sh, ch := sinhcosh(imag(x))
+	return complex(c*ch, -s*sh)
+}
+
+// Complex hyperbolic cosine
+//
+// DESCRIPTION:
+//
+// ccosh(z) = cosh x  cos y + i sinh x sin y .
+//
+// ACCURACY:
+//
+//                      Relative error:
+// arithmetic   domain     # trials      peak         rms
+//    IEEE      -10,+10     30000       2.9e-16     8.1e-17
+
+// Cosh returns the hyperbolic cosine of x.
+func Cosh(x complex128) complex128 {
+	s, c := math.Sincos(imag(x))
+	sh, ch := sinhcosh(real(x))
+	return complex(c*ch, s*sh)
+}
+
+// calculate sinh and cosh
+func sinhcosh(x float64) (sh, ch float64) {
+	if math.Abs(x) <= 0.5 {
+		return math.Sinh(x), math.Cosh(x)
+	}
+	e := math.Exp(x)
+	ei := 0.5 / e
+	e *= 0.5
+	return e - ei, e + ei
+}