Add div_with_overflow (#106)

* Remove promoting with_overflow functions.

* Bump Project.toml: 0.5.6

---------

Co-authored-by: Nathan Daly <[email protected]>

Project.toml

@@ -1,7 +1,7 @@
 name = "FixedPointDecimals"
 uuid = "fb4d412d-6eee-574d-9565-ede6634db7b0"
 authors = ["Fengyang Wang <[email protected]>", "Curtis Vogt <[email protected]>"]
-version = "0.5.5"
+version = "0.5.6"
 
 [deps]
 BitIntegers = "c3b6d118-76ef-56ca-8cc7-ebb389d030a1"

src/FixedPointDecimals.jl

@@ -32,7 +32,7 @@ export FixedDecimal, RoundThrows
 
 # (Re)export checked_* arithmetic functions
 # - Defined in this package:
-export checked_rdiv
+export checked_rdiv, div_with_overflow
 # - Reexported from Base:
 export checked_abs, checked_add, checked_cld, checked_div, checked_fld,
     checked_mod, checked_mul, checked_neg, checked_rem, checked_sub
@@ -441,6 +441,27 @@ Base.Checked.mul_with_overflow(x::FD, y::FD) = Base.Checked.mul_with_overflow(pr
 Base.Checked.mul_with_overflow(x::FD, y) = Base.Checked.mul_with_overflow(promote(x, y)...)
 Base.Checked.mul_with_overflow(x, y::FD) = Base.Checked.mul_with_overflow(promote(x, y)...)
 
+# This does not exist in Base so is just part of this package.
+# Throws on divide by zero.
+@doc """
+    div_with_overflow(x::FixedDecimal{T,f}, y::FixedDecimal{T,f})::(FixedDecimal{T,f}, Bool)
+        where {T<:Integer, f}
+
+Return the result of div (wrapping on overflow/underflow) and a boolean indicating whether
+overflow/underflow did in fact happen. Throws a DivideError on divide-by-zero.
+"""
+function div_with_overflow(x::FD{T,f}, y::FD{T,f}) where {T<:Integer,f}
+    C = coefficient(FD{T, f})
+    # This case will break the div call below.
+    if x.i == typemin(T) && y.i == -1
+        # To perform the div and overflow means reaching the max and adding 1, so typemin.
+        return (x, true)
+    end
+    # Note: The div() will throw for divide-by-zero, that's not an overflow.
+    v, b = Base.Checked.mul_with_overflow(C, div(x.i, y.i))
+    return (reinterpret(FD{T,f}, v), b)
+end
+
 Base.checked_add(x::FD, y::FD) = Base.checked_add(promote(x, y)...)
 Base.checked_sub(x::FD, y::FD) = Base.checked_sub(promote(x, y)...)
 Base.checked_mul(x::FD, y::FD) = Base.checked_mul(promote(x, y)...)

test/FixedDecimal.jl

@@ -791,6 +791,10 @@ end
         @test Base.Checked.mul_with_overflow(FD{Int8,0}(120), 2) == (FD{Int8,0}(-16), true)
         @test Base.Checked.mul_with_overflow(120, FD{Int8,0}(2)) == (FD{Int8,0}(-16), true)
 
+        @test div_with_overflow(FD{Int8,2}(1), FD{Int8,2}(0.5)) == (FD{Int8,2}(-0.56), true)
+        @test div_with_overflow(typemin(FD{Int32,0}), FD{Int32,0}(-1)) == (typemin(FD{Int32,0}), true)
+        @test div_with_overflow(FD{Int16,1}(1639), FD{Int16,1}(0.5)) == (FD{Int16,1}(-3275.6), true)
+
         @testset "with_overflow math corner cases" begin
             @testset for I in (Int128, UInt128, Int8, UInt8), f in (0,2)
             T = FD{I, f}
@@ -816,6 +820,16 @@ end
                     issigned(I) && @test Base.Checked.mul_with_overflow(typemin(T), 2) == (typemin(T) * 2, true)
                     issigned(I) && @test Base.Checked.mul_with_overflow(2, typemin(T)) == (2 * typemin(T), true)
                 end
+
+                if f > 0
+                    @test div_with_overflow(typemax(T), eps(T))[2]
+                    issigned(I) && @test div_with_overflow(typemin(T), eps(T))[2]
+                    issigned(I) && @test div_with_overflow(typemax(T), -eps(T))[2]
+
+                    issigned(I) && @test_throws DivideError div_with_overflow(typemax(T), T(0))
+                    issigned(I) && @test_throws DivideError div_with_overflow(typemin(T), T(0))
+                    issigned(I) && @test div_with_overflow(typemin(T), -eps(T))[2]
+                end
             end
         end
 
@@ -849,6 +863,12 @@ end
             @test Base.Checked.mul_with_overflow(FD{Int64,6}(2.22), 4) == (FD{Int64,6}(8.88), false)
             @test Base.Checked.mul_with_overflow(FD{Int128,14}(10), FD{Int128,14}(20.1)) == (FD{Int128,14}(201), false)
             @test Base.Checked.mul_with_overflow(FD{Int128,30}(10.11), FD{Int128,0}(1)) == (FD{Int128,30}(10.11), false)
+
+            @test div_with_overflow(FD{Int64,6}(4), FD{Int64,6}(2)) == (FD{Int64,6}(2), false)
+            @test div_with_overflow(FD{Int32,6}(4), FD{Int32,6}(2.1)) == (FD{Int32,6}(1), false)
+            @test div_with_overflow(FD{Int128,14}(10), FD{Int128,14}(20.1)) == (FD{Int128,14}(0), false)
+            @test div_with_overflow(FD{Int128,30}(10.1), FD{Int128,30}(1)) == (FD{Int128,30}(10), false)
+            @test div_with_overflow(typemin(FD{Int32,8}(1)), FD{Int32,8}(-1)) == (21, false)
         end
     end