Raise an error when seed! Xorshifts RNGs with 0. Fix #48.

Author: sunoru

docs/src/man/xorshifts.md

@@ -42,7 +42,7 @@ julia> using RandomNumbers.Xorshifts
 
 julia> r = Xoroshiro128Plus();  # create a RNG with truly random seed.
 
-julia> r = Xoroshiro128Plus(0x1234567890abcdef)  # with a certain seed.
+julia> r = Xoroshiro128Plus(0x1234567890abcdef)  # with a certain seed. Note that the seed must be non-zero.
 RandomNumbers.Xorshifts.Xoroshiro128Plus(0x13c5b80b0f92f3ac, 0xcdd3f80fa9fb6887)
 
 julia> rand(r)

src/Xorshifts/docs.jl

@@ -9,7 +9,7 @@ $r <: AbstractXorshift64
 $r([seed])
 ```
 
-$r RNG. The `seed` will be automatically convert to an `UInt64` number.
+$r RNG. The `seed` will be automatically convert to an `UInt64` number. A zero seed is not acceptable.
 """
     @doc doc_xorshift64("Xorshift64") Xorshift64
     @doc doc_xorshift64("Xorshift64Star") Xorshift64Star
@@ -22,7 +22,7 @@ $r([seed])
 ```
 
 $r RNG. The `seed` can be a `Tuple` of two `UInt64`s, or an `Integer` which will be automatically convert to
-an `UInt128` number.
+an `UInt128` number. Zero seeds are not acceptable.
 """
     @doc doc_xorshift128("Xorshift128") Xorshift128
     @doc doc_xorshift128("Xorshift128Star") Xorshift128Star
@@ -36,7 +36,7 @@ $r([seed...])
 ```
 
 $r RNG. The `seed` can be a `Tuple` of 16 `UInt64`s, or several (no more than 16) `Integer`s which will all
-be automatically converted to `UInt64` numbers.
+be automatically converted to `UInt64` numbers. Zero seeds are not acceptable.
 """
     @doc doc_xorshift1024("Xorshift1024") Xorshift1024
     @doc doc_xorshift1024("Xorshift1024Star") Xorshift1024Star
@@ -50,7 +50,7 @@ $r([seed])
 ```
 
 $r RNG. The `seed` can be a `Tuple` of two `UInt64`s, or an `Integer` which will be automatically convert to
-an `UInt128` number.
+an `UInt128` number. Zero seeds are not acceptable.
 """
     @doc doc_xoroshiro128("Xoroshiro128") Xoroshiro128
     @doc doc_xoroshiro128("Xoroshiro128Star") Xoroshiro128Star

src/Xorshifts/xoroshiro128.jl

@@ -57,6 +57,7 @@ copy(src::T) where T <: AbstractXoroshiro128 = copyto!(T(), src)
 
 seed!(r::AbstractXoroshiro128, seed::Integer) = seed!(r, split_uint(seed % UInt128))
 function seed!(r::AbstractXoroshiro128, seed::NTuple{2, UInt64}=gen_seed(UInt64, 2))
+    all(==(0), seed) && error("0 cannot be the seed")
     r.x = seed[1]
     r.y = seed[2]
     xorshift_next(r)

src/Xorshifts/xorshift1024.jl

@@ -84,6 +84,7 @@ copy(src::T) where T <: AbstractXorshift1024 = copyto!(T(), src)
 ==(r1::T, r2::T) where T <: AbstractXorshift1024 = unsafe_compare(r1, r2, UInt64, 16) && r1.p == r2.p
 
 function seed!(r::AbstractXorshift1024, seed::NTuple{16, UInt64})
+    all(==(0), seed) && error("0 cannot be the seed")
     ptr = Ptr{UInt64}(pointer_from_objref(r))
     @inbounds for i in 1:16
         unsafe_store!(ptr, seed[i], i)

src/Xorshifts/xorshift128.jl

@@ -55,6 +55,7 @@ copy(src::T) where T <: AbstractXorshift128 = copyto!(T(), src)
 seed!(r::AbstractXorshift128, seed::Integer) = seed!(r, split_uint(seed % UInt128))
 
 function seed!(r::AbstractXorshift128, seed::NTuple{2, UInt64}=gen_seed(UInt64, 2))
+    all(==(0), seed) && error("0 cannot be the seed")
     r.x = seed[1]
     r.y = seed[2]
     xorshift_next(r)

src/Xorshifts/xorshift64.jl

@@ -46,6 +46,7 @@ copy(src::T) where T <: AbstractXorshift64 = copyto!(T(), src)
 ==(r1::T, r2::T) where T <: AbstractXorshift64 = r1.x == r2.x
 
 function seed!(r::AbstractXorshift64, seed::Integer=gen_seed(UInt64))
+    seed == 0 && error("0 cannot be the seed")
     r.x = seed % UInt64
     xorshift_next(r)
     r

test/Xorshifts/runtests.jl

@@ -36,6 +36,10 @@ for (rng_name, seed_t) in (
     redirect_stdout(outfile)
 
     @eval x = $rng_name()
+    @test_throws(
+        ErrorException("0 cannot be the seed"),
+        seed_t === NTuple{16, UInt64} ? seed!(x, zeros(UInt64, 16)...) : seed!(x, 0)
+    )
     seed!(x)
     @test seed_type(x) == seed_t
     @test copyto!(copy(x), x) == x
@@ -54,5 +58,6 @@ for (rng_name, seed_t) in (
 end
 redirect_stdout(stdout_)
 
+
 compare_dirs("expected", "actual")
 cd(pwd_)

test/common.jl

@@ -1,6 +1,6 @@
 using RandomNumbers
 import Random: seed!
-using Test: @test
+using Test: @test, @test_throws
 using Base.Printf: @printf
 
 function compare_dirs(dir1::AbstractString, dir2::AbstractString)