add shuffle implementation to preserve stability (#17)

.github/workflows/CI.yml

@@ -20,6 +20,14 @@ jobs:
       matrix:
         version:
           - "1.0"  # earliest supported release
+          - "1.1"
+          - "1.2"
+          - "1.3"
+          - "1.4"
+          - "1.5"
+          - "1.6"
+          - "1.7"
+          - "1.8"
           - "1"    # latest release
           - "nightly"
         os:

Project.toml

@@ -1,7 +1,7 @@
 name    = "StableRNGs"
 uuid    = "860ef19b-820b-49d6-a774-d7a799459cd3"
 authors = ["Rafael Fourquet <[email protected]>"]
-version = "1.0.0"
+version = "1.0.1"
 
 [deps]
 Random = "9a3f8284-a2c9-5f02-9a11-845980a1fd5c"

src/StableRNGs.jl

@@ -6,6 +6,13 @@ using Random: Random, AbstractRNG, Sampler, SamplerType
 
 import Random: rand, seed!
 
+# Compat
+if VERSION < v"1.2.0-"
+    using Base: has_offset_axes
+    require_one_based_indexing(A...) = !has_offset_axes(A...) || throw(ArgumentError("offset arrays are not supported but got an array with index other than 1"))
+else
+    using Base: require_one_based_indexing
+end
 
 # implementation of LehmerRNG based on the constants found at the
 # MIT licensed code by Melissa E. O'Neill at
@@ -132,5 +139,20 @@ for T in Base.BitInteger_types
         SamplerRangeFast(r)
 end
 
+# https://github.com/JuliaRandom/StableRNGs.jl/issues/10
+Random.shuffle(r::StableRNG, a::AbstractArray) = Random.shuffle!(r, Base.copymutable(a))
+function Random.shuffle!(r::StableRNG, a::AbstractArray)
+    require_one_based_indexing(a)
+    n = length(a)
+    n <= 1 && return a # nextpow below won't work with n == 0
+    @assert n <= Int64(2)^52
+    mask = nextpow(2, n) - 1
+    for i = n:-1:2
+        (mask >> 1) == i && (mask >>= 1)
+        j = 1 + rand(r, Random.ltm52(i, mask))
+        a[i], a[j] = a[j], a[i]
+    end
+    return a
+end
 
 end # module

test/runtests.jl

@@ -131,15 +131,11 @@ end
     end
 end
 
+# Reference test
 @testset "`shuffle` stability" begin
     a = 1:10
     a_shuffled = [4, 5, 6, 1, 3, 7, 10, 2, 8, 9]
-
-    # If these tests fail due to changes in the algorithm used in `Random.shuffle`,
-    # we should vendor the old implementation here to keep it stable.
-    # See <https://github.com/JuliaRandom/StableRNGs.jl/issues/10>.
-    @test shuffle(StableRNG(10), a) == a_shuffled 
-
+    @test shuffle(StableRNG(10), a) == a_shuffled
     b = collect(a)
     shuffle!(StableRNG(10), b)
     @test b == a_shuffled