add cutoff for integer conversion

Author: araujoms

src/math/elementary/explog.jl

@@ -120,8 +120,8 @@ function Base.:(^)(r::DoubleFloat{T}, n::Int) where {T<:IEEEFloat}
 end
 
 function Base.:(^)(r::DoubleFloat{T}, n::DoubleFloat{T}) where {T <: IEEEFloat}
-    if isinteger(n)
-        return r^Int64(Float64(n)) # convert n to Float64 first
+    if isinteger(n) && n ≤ min(2^20, intmaxfloat(T, Int64))
+        return r^Int64(n.hi)
     else
         return exp(n * log(r))
     end