Make FD÷FD return an FD. (#40)

* Make FD÷FD return an FD.

Before this, `FD{T,f} ÷ FD{T,f}` returned `T`, now it returns `FD{T,f}`.

Same for `div`, `fld`, and `fld`.

* Add some simple unit tests for ÷

There weren't any tests of `div` before, so this adds some simple ones.

* Add comment explaining why div() doesn't need widening logic

* Fix div (÷) tests to actually test output type

* Include explicit test of Return Types

Author: NHDaly

src/FixedPointDecimals.jl

@@ -300,7 +300,9 @@ for remfn in [:rem, :mod, :mod1, :min, :max]
     @eval $remfn(x::T, y::T) where {T <: FD} = reinterpret(T, $remfn(x.i, y.i))
 end
 for divfn in [:div, :fld, :fld1]
-    @eval $divfn(x::T, y::T) where {T <: FD} = $divfn(x.i, y.i)
+    # div(x.i, y.i) eliminates the scaling coefficient, so we call the FD constructor.
+    # We don't need any widening logic, since we won't be multiplying by the coefficient.
+    @eval $divfn(x::T, y::T) where {T <: FD} = T($divfn(x.i, y.i))
 end
 
 convert(::Type{AbstractFloat}, x::FD) = convert(floattype(typeof(x)), x)

test/runtests.jl

@@ -508,6 +508,36 @@ end
     end
 end
 
+@testset "truncating div" begin
+    @testset "div by 1" begin
+        @testset for x in keyvalues[FD2]
+            @test x ÷ one(x) === trunc(x)
+
+            # signed integers using two's complement have one additional negative value
+            if x < 0 && trunc(x) === typemin(x)
+                @test_throws InexactError x ÷ -one(x)
+            else
+                @test x ÷ -one(x) === -trunc(x)
+            end
+        end
+    end
+    @testset "div by 2" begin
+        @testset for x in keyvalues[FD2]
+            @test x ÷ 2one(x) === x ÷ 2 === FD2(x.i ÷ FD2(2).i)
+        end
+    end
+    @testset "return types" begin
+        @test div(2one(FD2), 3) isa FD2
+        @test one(FD2) ÷ one(FD2) isa FD2
+
+        # Promotion to bigger type
+        @test one(FD4) ÷ one(FD2) isa FD4
+        @test one(FD2) ÷ one(FD4) isa FD4
+
+        @test one(FD{Int32, 2}) ÷ one(FD{Int64, 6}) isa FD{Int64, 6}
+    end
+end
+
 @testset "abs, sign" begin
     @testset for T in [FD2, WFD4]
         for x in keyvalues[T]