Backport #401 and prepare release of SpecialFunctions 1.8.6 (#402)

* Fix `beta_inc_inv` bug introduced in #399 (#401)

* Release 1.8.6

Author: devmotion

Project.toml

@@ -1,6 +1,6 @@
 name = "SpecialFunctions"
 uuid = "276daf66-3868-5448-9aa4-cd146d93841b"
-version = "1.8.5"
+version = "1.8.6"
 
 [deps]
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"

src/beta_inc.jl

@@ -967,7 +967,7 @@ function _beta_inc_inv(a::Float64, b::Float64, p::Float64, q::Float64=1-p)
     sq = 1.0
     prev = 1.0
 
-    x = clamp(x, fpu, prevfloat(1.0))
+    x = clamp(x, 0.0001, 0.9999)
 
     # This first argument was proposed in
     #

test/beta_inc.jl

@@ -305,4 +305,10 @@ end
         y = 2.0e-280
         @test beta_inc(2.0, 1.0, beta_inc_inv(2.0, 1.0, y, 1.0)[1])[1] ≈ y
     end
+
+    @testset "StatsFuns#145" begin
+        y = 0.92
+        @test beta_inc_inv(0.01, 0.1, y)[1] ≈ 0.7803014210919872
+        @test beta_inc(0.01, 0.1, beta_inc_inv(0.01, 0.1, y)[1])[1] ≈ y
+    end
 end