unify shuffle and randperm (JuliaLang#50318)

Author: ctarn

stdlib/Random/src/misc.jl

@@ -201,34 +201,35 @@ julia> rng = MersenneTwister(1234);
 
 julia> shuffle!(rng, Vector(1:16))
 16-element Vector{Int64}:
-  2
- 15
-  5
- 14
+ 16
   1
-  9
+ 14
+ 12
+  5
  10
-  6
- 11
+  4
+ 15
+ 13
   3
- 16
   7
-  4
- 12
+  9
+  6
+ 11
   8
- 13
+  2
 ```
 """
 function shuffle!(r::AbstractRNG, a::AbstractArray)
+    # keep it consistent with `randperm!` and `randcycle!` if possible
     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)
+    n == 0 && return a
+    mask = 3
+    @inbounds for i = 2:n
         j = 1 + rand(r, ltm52(i, mask))
         a[i], a[j] = a[j], a[i]
+        i == 1 + mask && (mask = 2 * mask + 1)
     end
     return a
 end
@@ -249,16 +250,16 @@ julia> rng = MersenneTwister(1234);
 
 julia> shuffle(rng, Vector(1:10))
 10-element Vector{Int64}:
-  6
-  1
- 10
   2
-  3
+  1
+  7
   9
   5
-  7
+ 10
   4
   8
+  6
+  3
 ```
 """
 shuffle(r::AbstractRNG, a::AbstractArray) = shuffle!(r, copymutable(a))
@@ -315,6 +316,7 @@ julia> randperm!(MersenneTwister(1234), Vector{Int}(undef, 4))
 ```
 """
 function randperm!(r::AbstractRNG, a::Array{<:Integer})
+    # keep it consistent with `shuffle!` and `randcycle!` if possible
     n = length(a)
     @assert n <= Int64(2)^52
     n == 0 && return a
@@ -326,7 +328,7 @@ function randperm!(r::AbstractRNG, a::Array{<:Integer})
             a[i] = a[j]
         end
         a[j] = i
-        i == 1+mask && (mask = 2mask + 1)
+        i == 1 + mask && (mask = 2 * mask + 1)
     end
     return a
 end
@@ -382,16 +384,17 @@ julia> randcycle!(MersenneTwister(1234), Vector{Int}(undef, 6))
 ```
 """
 function randcycle!(r::AbstractRNG, a::Array{<:Integer})
+    # keep it consistent with `shuffle!` and `randperm!` if possible
     n = length(a)
-    n == 0 && return a
     @assert n <= Int64(2)^52
+    n == 0 && return a
     a[1] = 1
     mask = 3
     @inbounds for i = 2:n
         j = 1 + rand(r, ltm52(i-1, mask))
         a[i] = a[j]
         a[j] = i
-        i == 1+mask && (mask = 2mask + 1)
+        i == 1 + mask && (mask = 2 * mask + 1)
     end
     return a
 end