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

src/pkg/math/gamma.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 http://netlib.sandia.gov/cephes/cprob/gamma.c.
 // The go code is a simplified version of the original C.
 //
@@ skipping 103 matching lines @@
 //
 // Special cases are:
 //      Gamma(±Inf) = ±Inf
 //      Gamma(NaN) = NaN
 // Large values overflow to +Inf.
 // Negative integer values equal ±Inf.
 func Gamma(x float64) float64 {
         const Euler = 0.57721566490153286060651209008240243104215933593992 // A001620
         // special cases
         switch {
-        case x < -MaxFloat64 || x != x: // IsInf(x, -1) || IsNaN(x):
+        case IsInf(x, -1) || IsNaN(x):
                 return x
         case x < -170.5674972726612 || x > 171.61447887182298:
                 return Inf(1)
         }
         q := Abs(x)
         p := Floor(q)
         if q > 33 {
                 if x >= 0 {
                         return stirling(x)
                 }
@@ skipping 43 matching lines @@
         p = (((((x*_gamP[0]+_gamP[1])*x+_gamP[2])*x+_gamP[3])*x+_gamP[4])*x+_gamP[5])*x + _gamP[6]
         q = ((((((x*_gamQ[0]+_gamQ[1])*x+_gamQ[2])*x+_gamQ[3])*x+_gamQ[4])*x+_gamQ[5])*x+_gamQ[6])*x + _gamQ[7]
         return z * p / q
 
 small:
         if x == 0 {
                 return Inf(1)
         }
         return z / ((1 + Euler*x) * x)
 }