Make results of floor, trunc, ceil consistent (#76)

Author: omus

src/FixedPointDecimals.jl

@@ -125,14 +125,17 @@ function ceil{T, f}(x::FD{T, f})
     end
 end
 
-for truncfn in [:trunc, :floor, :ceil]
-    @eval $truncfn{TI <: Integer}(::Type{TI}, x::FD)::TI = $truncfn(x)
+for fn in [:trunc, :floor, :ceil]
+    @eval $fn{TI <: Integer}(::Type{TI}, x::FD)::TI = $fn(x)
 
     # round/trunc/ceil/flooring to FD; generic
     # TODO. this is probably incorrect for floating point and we need to check
     # overflow in other cases.
-    @eval function $truncfn{T, f}(::Type{FD{T, f}}, x::Real)
-        reinterpret(FD{T, f}, $truncfn(T, T(10)^f * x))
+    @eval function $fn{T, f}(::Type{FD{T, f}}, x::Real)
+        powt = T(10)^f
+        val = trunc(T, x)
+        val = val * powt + $fn(T, (x - val) * powt)
+        reinterpret(FD{T, f}, val)
     end
 end
 round{TI <: Integer}(::Type{TI}, x::FD,

test/runtests.jl

@@ -1,11 +1,13 @@
 using FixedPointDecimals
+import FixedPointDecimals: FD
 using Base.Test
 using Compat
 
 const SFD2 = FixedDecimal{Int16, 2}
 const SFD4 = FixedDecimal{Int16, 4}
 const FD1 = FixedDecimal{Int, 1}
 const FD2 = FixedDecimal{Int, 2}
+const FD3 = FixedDecimal{Int, 3}
 const FD4 = FixedDecimal{Int, 4}
 const WFD2 = FixedDecimal{Int128, 2}
 const WFD4 = FixedDecimal{Int128, 4}
@@ -37,12 +39,22 @@ const keyvalues = Dict(
              reinterpret(WFD4, 164435910993133062409572187012743929911),
              typemax(WFD4)])
 
+# Floating point values written as integer strings. Useful for testing behaviours of
+# trunc, floor, and ceil.
+const INT_2_2 = "22000000000000001776356839400250464677"  # 2.2
+const INT_2_3 = "22999999999999998223643160599749535322"  # 2.3
+
+
 # numbers that may cause overflow
 islarge(x) = x == typemin(x) || abs(x) > 1000
 
 # numbers that can never cause overflow
 issmall(x) = -1 < x ≤ 1
 
+function parse_int{T, f}(::Type{FD{T, f}}, val::AbstractString; ceil::Bool=false)
+    reinterpret(FD{T, f}, parse(T, val[1:(f + 1)]) + T(ceil))
+end
+
 @testset "conversion" begin
     @testset for x in keyvalues[FD2]
         @testset for T in [Rational{Int128}, WFD2, WFD4]
@@ -285,6 +297,16 @@ end
         @test isinteger(Base.widemul(10, FD2(trunc(FD1, x))))
         @test abs(FD2(trunc(FD1, x))) ≥ 0
     end
+
+    @testset "truncate precision" begin
+        @test trunc(FD2, 2.3) != trunc(FD3, 2.3)
+        @test trunc(FD2, 2.3) == FD2(2.29)
+        @test trunc(FD3, 2.3) == FD3(2.299)
+
+        for f in 0:12
+            trunc(FD{Int64, f}, 2.3) == parse_int(FD{Int64, f}, INT_2_3)
+        end
+    end
 end
 
 # eps that works for integers too
@@ -303,6 +325,24 @@ epsi{T}(::Type{T}) = eps(T)
             @test ceil(T, x) - epsi(T) < x ≤ ceil(T, x)
         end
     end
+
+    @testset "floor, ceil precision" begin
+        @test floor(FD2, 2.3) != floor(FD3, 2.3)
+        @test floor(FD2, 2.3) == FD2(2.29)
+        @test floor(FD3, 2.3) == FD3(2.299)
+
+        for f in 0:12
+            floor(FD{Int64, f}, 2.3) == parse_int(FD{Int64, f}, INT_2_3)
+        end
+
+        @test ceil(FD2, 2.2) != ceil(FD3, 2.2)
+        @test ceil(FD2, 2.2) == FD2(2.21)
+        @test ceil(FD3, 2.2) == FD3(2.201)
+
+        for f in 0:12
+            ceil(FD{Int64, f}, 2.2) == parse_int(FD{Int64, f}, INT_2_2, ceil=true)
+        end
+    end
 end
 
 @testset "show" begin