Add method to rationalize Rational (#43427)

* Add Method to Rationalize Rational and Integer Co-authored-by: Jeff Bezanson <[email protected]> Co-authored-by: Oscar Smith <[email protected]>
JuliaLang · Jun 14, 2023 · 8a1b642 · 8a1b642
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Showing 2 changed files with 28 additions and 5 deletions.
diff --git a/base/rational.jl b/base/rational.jl
@@ -173,10 +173,11 @@ julia> typeof(numerator(a))
 BigInt
 ```
 """
-function rationalize(::Type{T}, x::AbstractFloat, tol::Real) where T<:Integer
+function rationalize(::Type{T}, x::Union{AbstractFloat, Rational}, tol::Real) where T<:Integer
     if tol < 0
         throw(ArgumentError("negative tolerance $tol"))
     end
+
     T<:Unsigned && x < 0 && __throw_negate_unsigned()
     isnan(x) && return T(x)//one(T)
     isinf(x) && return unsafe_rational(x < 0 ? -one(T) : one(T), zero(T))
@@ -188,7 +189,6 @@ function rationalize(::Type{T}, x::AbstractFloat, tol::Real) where T<:Integer
     a = trunc(x)
     r = x-a
     y = one(x)
-
     tolx = oftype(x, tol)
     nt, t, tt = tolx, zero(tolx), tolx
     ia = np = nq = zero(T)
@@ -233,10 +233,21 @@ function rationalize(::Type{T}, x::AbstractFloat, tol::Real) where T<:Integer
         return p // q
     end
 end
-rationalize(::Type{T}, x::AbstractFloat; tol::Real = eps(x)) where {T<:Integer} = rationalize(T, x, tol)::Rational{T}
+rationalize(::Type{T}, x::AbstractFloat; tol::Real = eps(x)) where {T<:Integer} = rationalize(T, x, tol)
 rationalize(x::AbstractFloat; kvs...) = rationalize(Int, x; kvs...)
-rationalize(::Type{T}, x::Complex; kvs...) where {T<:Integer} = Complex(rationalize(T, x.re, kvs...)::Rational{T}, rationalize(T, x.im, kvs...)::Rational{T})
-rationalize(x::Complex; kvs...) = Complex(rationalize(Int, x.re, kvs...), rationalize(Int, x.im, kvs...))
+rationalize(::Type{T}, x::Complex; kvs...) where {T<:Integer} = Complex(rationalize(T, x.re; kvs...), rationalize(T, x.im; kvs...))
+rationalize(x::Complex; kvs...) = Complex(rationalize(Int, x.re; kvs...), rationalize(Int, x.im; kvs...))
+rationalize(::Type{T}, x::Rational; tol::Real = 0) where {T<:Integer} = rationalize(T, x, tol)
+rationalize(x::Rational; kvs...) = x
+rationalize(x::Integer; kvs...) = Rational(x)
+function rationalize(::Type{T}, x::Integer; kvs...) where {T<:Integer}
+    if Base.hastypemax(T) # BigInt doesn't
+        x < typemin(T) && return unsafe_rational(-one(T), zero(T))
+        x > typemax(T) && return unsafe_rational(one(T), zero(T))
+    end
+    return Rational{T}(x)
+end
+
 
 """
     numerator(x)

diff --git a/test/rational.jl b/test/rational.jl
@@ -33,6 +33,11 @@ using Test
 
     @test @inferred(rationalize(Int, 3.0, 0.0)) === 3//1
     @test @inferred(rationalize(Int, 3.0, 0)) === 3//1
+    @test @inferred(rationalize(Int, 33//100; tol=0.1)) === 1//3 # because tol
+    @test @inferred(rationalize(Int, 3; tol=0.0)) === 3//1
+    @test @inferred(rationalize(Int8, 1000//333)) === Rational{Int8}(3//1)
+    @test @inferred(rationalize(Int8, 1000//3)) === Rational{Int8}(1//0)
+    @test @inferred(rationalize(Int8, 1000)) === Rational{Int8}(1//0)
     @test_throws OverflowError rationalize(UInt, -2.0)
     @test_throws ArgumentError rationalize(Int, big(3.0), -1.)
     # issue 26823
@@ -727,3 +732,10 @@ end
     @test rationalize(1.192 + 2.233im) == 149//125 + 2233//1000*im
     @test rationalize(Int8, 1.192 + 2.233im) == 118//99 + 67//30*im
 end
+@testset "rationalize(Complex) with tol" begin
+    # test: rationalize(x::Complex; kvs...)
+    precise_next = 7205759403792795//72057594037927936
+    @assert Float64(precise_next) == nextfloat(0.1)
+    @test rationalize(nextfloat(0.1) * im; tol=0) == precise_next * im
+    @test rationalize(0.1im; tol=eps(0.1)) == rationalize(0.1im)
+end