code review 5484076: pkg/math: undo manual inlining of IsInf and IsNaN

src/pkg/math/atanh.go

 // 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 math
 
 // The original C code, the long comment, and the constants
 // below are from FreeBSD's /usr/src/lib/msun/src/e_atanh.c
 // and came with this notice.  The go code is a simplified
 // version of the original C.
@@ skipping 28 matching lines @@
 // Atanh(x) calculates the inverse hyperbolic tangent of x.
 //
 // Special cases are:
 //      Atanh(1) = +Inf
 //      Atanh(±0) = ±0
 //      Atanh(-1) = -Inf
 //      Atanh(x) = NaN if x < -1 or x > 1
 //      Atanh(NaN) = NaN
 func Atanh(x float64) float64 {
         const NearZero = 1.0 / (1 << 28) // 2**-28
-        // TODO(rsc): Remove manual inlining of IsNaN
-        // when compiler does it for us
         // special cases
         switch {
-        case x < -1 || x > 1 || x != x: // x < -1 || x > 1 || IsNaN(x):
+        case x < -1 || x > 1 || IsNaN(x):
                 return NaN()
         case x == 1:
                 return Inf(1)
         case x == -1:
                 return Inf(-1)
         }
         sign := false
         if x < 0 {
                 x = -x
                 sign = true
         }
         var temp float64
         switch {
         case x < NearZero:
                 temp = x
         case x < 0.5:
                 temp = x + x
                 temp = 0.5 * Log1p(temp+temp*x/(1-x))
         default:
                 temp = 0.5 * Log1p((x+x)/(1-x))
         }
         if sign {
                 temp = -temp
         }
         return temp
 }