Quick return for linspace when start == stop. Fixes JuliaLang#20520. (J…

…uliaLang#20537)

The old code worked in the case where the inputs are expressible as rationals, but when that fails we were getting an InexactError.

base/twiceprecision.jl

@@ -318,6 +318,9 @@ end
 # For Float16, Float32, and Float64, linspace returns a StepRangeLen
 function linspace{T<:Union{Float16,Float32,Float64}}(start::T, stop::T, len::Integer)
  len < 2 && return _linspace1(T, start, stop, len)
+ if start == stop
+ return StepRangeLen(TwicePrecision(start,zero(T)), TwicePrecision(zero(T),zero(T)), len)
+ end
  # Attempt to find exact rational approximations
  start_n, start_d = rat(start)
  stop_n, stop_d = rat(stop)

test/ranges.jl

@@ -867,6 +867,14 @@ let r = linspace(-big(1.0),big(1.0),4)
  @test r[2] ≈ big(-1.0)/3
 end
 
+# issue #20520
+let r = linspace(1.3173739f0, 1.3173739f0, 3)
+ @test length(r) == 3
+ @test first(r) === 1.3173739f0
+ @test last(r) === 1.3173739f0
+ @test r[2] === 1.3173739f0
+end
+
 let r = linspace(1.0, 3+im, 4)
  @test r[1] === 1.0+0.0im
  @test r[2] ≈ (5/3)+(1/3)im