code review 4035044: Update to current version of Go library.

libgo/go/math/ldexp.go

 // Copyright 2009 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
 
 // Ldexp is the inverse of Frexp.
 // It returns frac × 2**exp.
+//
+// Special cases are:
+//      Ldexp(±0, exp) = ±0
+//      Ldexp(±Inf, exp) = ±Inf
+//      Ldexp(NaN, exp) = NaN
 func Ldexp(frac float64, exp int) float64 {
         // TODO(rsc): Remove manual inlining of IsNaN, IsInf
         // when compiler does it for us
         // special cases
         switch {
         case frac == 0:
                 return frac // correctly return -0
-        case frac != frac: // IsNaN(frac):
-                return NaN()
+        case frac < -MaxFloat64 || frac > MaxFloat64 || frac != frac: // IsInf(frac, 0) || IsNaN(frac):
+                return frac
         }
+        frac, e := normalize(frac)
+        exp += e
         x := Float64bits(frac)
-        exp += int(x>>shift) & mask
-        if exp <= 0 {
-                return 0 // underflow
+        exp += int(x>>shift)&mask - bias
+        if exp < -1074 {
+                return Copysign(0, frac) // underflow
         }
-        if exp >= mask { // overflow
+        if exp > 1023 { // overflow
                 if frac < 0 {
                         return Inf(-1)
                 }
                 return Inf(1)
         }
+        var m float64 = 1
+        if exp < -1022 { // denormal
+                exp += 52
+                m = 1.0 / (1 << 52) // 2**-52
+        }
         x &^= mask << shift
-        x |= uint64(exp) << shift
-        return Float64frombits(x)
+        x |= uint64(exp+bias) << shift
+        return m * Float64frombits(x)
 }