Merge pull request JuliaLang#11178 from ScottPJones/spj/randchar

Simplify and improve performance of rand(Char)

base/random.jl

@@ -253,14 +253,10 @@ rand(r::MersenneTwister, ::Type{Int128}) = reinterpret(Int128, rand(r, UInt128)
 rand{T<:Real}(r::AbstractRNG, ::Type{Complex{T}}) = complex(rand(r, T), rand(r, T))
 
 # random Char values
-# use simple rejection sampling over valid Char codepoint range
+# returns a random valid Unicode scalar value (i.e. 0 - 0xd7ff, 0xe000 - # 0x10ffff)
 function rand(r::AbstractRNG, ::Type{Char})
- while true
- c = rand(0x00000000:0x0010fffd)
- if is_valid_char(c)
- return reinterpret(Char,c)
- end
- end
+ c = rand(0x00000000:0x0010f7ff)
+ (c < 0xd800) ? Char(c) : Char(c+0x800)
 end
 
 ## Arrays of random numbers