From 0209c30bc920e732a04adfbacdd28376834cc912 Mon Sep 17 00:00:00 2001
From: Juan Ignacio Polanco <jipolanc@gmail.com>
Date: Wed, 23 Feb 2022 21:07:30 +0100
Subject: [PATCH] Make sure `range(start; step, length)` uses TwicePrecision
 when possible, fixes #44292. (#44313)

---
 base/twiceprecision.jl | 12 ++++++++++--
 test/ranges.jl         | 12 ++++++++++++
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/base/twiceprecision.jl b/base/twiceprecision.jl
index 8f80b2c8438a03..6d91431e47abbb 100644
--- a/base/twiceprecision.jl
+++ b/base/twiceprecision.jl
@@ -408,7 +408,7 @@ function floatrange(a::AbstractFloat, st::AbstractFloat, len::Real, divisor::Abs
     steprangelen_hp(T, (a,divisor), (st,divisor), nbitslen(T, len, 1), len, oneunit(len))
 end
 
-function (:)(start::T, step::T, stop::T) where T<:Union{Float16,Float32,Float64}
+function (:)(start::T, step::T, stop::T) where T<:IEEEFloat
     step == 0 && throw(ArgumentError("range step cannot be zero"))
     # see if the inputs have exact rational approximations (and if so,
     # perform all computations in terms of the rationals)
@@ -453,7 +453,10 @@ end
 step(r::StepRangeLen{T,TwicePrecision{T},TwicePrecision{T}}) where {T<:AbstractFloat} = T(r.step)
 step(r::StepRangeLen{T,TwicePrecision{T},TwicePrecision{T}}) where {T} = T(r.step)
 
-function range_start_step_length(a::T, st::T, len::Integer) where T<:Union{Float16,Float32,Float64}
+range_start_step_length(a, st::IEEEFloat, len::Integer) =
+    range_start_step_length(oftype(st, a), st, len)
+
+function range_start_step_length(a::T, st::T, len::Integer) where T<:IEEEFloat
     len = len + 0 # promote with Int
     start_n, start_d = rat(a)
     step_n, step_d = rat(st)
@@ -471,6 +474,11 @@ function range_start_step_length(a::T, st::T, len::Integer) where T<:Union{Float
     steprangelen_hp(T, a, st, 0, len, 1)
 end
 
+function range_step_stop_length(step::IEEEFloat, stop, len::Integer)
+    r = range_start_step_length(stop, negate(step), len)
+    reverse(r)
+end
+
 # This assumes that r.step has already been split so that (0:len-1)*r.step.hi is exact
 function unsafe_getindex(r::StepRangeLen{T,<:TwicePrecision,<:TwicePrecision}, i::Integer) where T
     # Very similar to _getindex_hiprec, but optimized to avoid a 2nd call to add12
diff --git a/test/ranges.jl b/test/ranges.jl
index a7f26c7efa6296..536c1f4710d9d1 100644
--- a/test/ranges.jl
+++ b/test/ranges.jl
@@ -1612,6 +1612,18 @@ end
     @test x isa StepRangeLen{Float64,Base.TwicePrecision{Float64},Base.TwicePrecision{Float64}}
 end
 
+@testset "Issue #44292" begin
+    let x = @inferred range(0, step=0.2, length=5)
+        @test x isa StepRangeLen{Float64,Base.TwicePrecision{Float64},Base.TwicePrecision{Float64}}
+        @test x == [0.0, 0.2, 0.4, 0.6, 0.8]
+    end
+
+    let x = @inferred range(stop=1, step=0.2, length=5)
+        @test x isa StepRangeLen{Float64,Base.TwicePrecision{Float64},Base.TwicePrecision{Float64}}
+        @test x == [0.2, 0.4, 0.6, 0.8, 1.0]
+    end
+end
+
 @testset "Views of ranges" begin
     @test view(Base.OneTo(10), Base.OneTo(5)) === Base.OneTo(5)
     @test view(1:10, 1:5) === 1:5