Fix isinteger at the input limits

Author: omus

src/FixedPointDecimals.jl

@@ -271,7 +271,7 @@ Base.@pure promote_rule{T, f, U, g}(::Type{FD{T, f}}, ::Type{FD{U, g}}) =
 <={T <: FD}(x::T, y::T) = x.i <= y.i
 
 # predicates and traits
-isinteger{T, f}(x::FD{T, f}) = rem(x.i, T(10)^f) == 0
+isinteger{T, f}(x::FD{T, f}) = rem(x.i, coefficient(FD{T, f})) == 0
 typemin{T, f}(::Type{FD{T, f}}) = reinterpret(FD{T, f}, typemin(T))
 typemax{T, f}(::Type{FD{T, f}}) = reinterpret(FD{T, f}, typemax(T))
 eps{T <: FD}(::Type{T}) = reinterpret(T, 1)

test/runtests.jl

@@ -458,6 +458,26 @@ end
     end
 end
 
+@testset "isinteger" begin
+    @testset "overflow" begin
+        # Note: After overflow `Int8(10)^6 == 64`
+        @test !isinteger(reinterpret(FD{Int8,6}, 64))  # 0.000064
+    end
+
+    @testset "limits of $T" for T in CONTAINER_TYPES
+        f = FixedPointDecimals.max_exp10(T)
+
+        max_fd = typemax(FD{T,f})
+        min_fd = typemin(FD{T,f})
+
+        @test !isinteger(max_fd)
+        @test isinteger(trunc(max_fd))
+
+        @test isinteger(min_fd) == (min_fd == zero(min_fd))
+        @test isinteger(trunc(min_fd))
+    end
+end
+
 @testset "round" begin
     @testset "to Int" begin
         @test round(Int, FD2(-0.51)) === -1