math: add special-cases comments to Sinh and Tanh.

Also change "Special conditions" to "Special cases" as in other functions.

R=rsc, golang-dev
CC=golang-dev
https://golang.org/cl/5440078

src/pkg/math/sin.go

@@ -110,7 +110,7 @@ var _cos = [...]float64{
 
 // Cos returns the cosine of x.
 //
-// Special conditions are:
+// Special cases are:
 //	Cos(±Inf) = NaN
 //	Cos(NaN) = NaN
 func Cos(x float64) float64 {

src/pkg/math/sincos.go

@@ -8,7 +8,7 @@ package math
 
 // Sincos(x) returns Sin(x), Cos(x).
 //
-// Special conditions are:
+// Special cases are:
 //	Sincos(±0) = ±0, 1
 //	Sincos(±Inf) = NaN, NaN
 //	Sincos(NaN) = NaN, NaN

src/pkg/math/sinh.go

@@ -17,6 +17,11 @@ package math
 */
 
 // Sinh returns the hyperbolic sine of x.
+//
+// Special cases are:
+//	Sinh(±0) = ±0
+//	Sinh(±Inf) = ±Inf
+//	Sinh(NaN) = NaN
 func Sinh(x float64) float64 {
 	// The coefficients are #2029 from Hart & Cheney. (20.36D)
 	const (
@@ -56,6 +61,11 @@ func Sinh(x float64) float64 {
 }
 
 // Cosh returns the hyperbolic cosine of x.
+//
+// Special cases are:
+//	Cosh(±0) = 1
+//	Cosh(±Inf) = +Inf
+//	Cosh(NaN) = NaN
 func Cosh(x float64) float64 {
 	if x < 0 {
 		x = -x

src/pkg/math/tan.go

@@ -75,7 +75,7 @@ var _tanQ = [...]float64{
 
 // Tan returns the tangent of x.
 //
-// Special conditions are:
+// Special cases are:
 //	Tan(±0) = ±0
 //	Tan(±Inf) = NaN
 //	Tan(NaN) = NaN

src/pkg/math/tanh.go

@@ -12,6 +12,11 @@ package math
 */
 
 // Tanh computes the hyperbolic tangent of x.
+//
+// Special cases are:
+//	Tanh(±0) = ±0
+//	Tanh(±Inf) = ±1
+//	Tanh(NaN) = NaN
 func Tanh(x float64) float64 {
 	if x < 0 {
 		x = -x