ismersenneprime: handle the very easy case M < 7

JuliaMath · Apr 18, 2017 · b2fe53a · b2fe53a
1 parent e528159
commit b2fe53a
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diff --git a/src/Primes.jl b/src/Primes.jl
@@ -429,6 +429,7 @@ function ismersenneprime(M::Integer; check::Bool = true)
         M >= 0 && isprime(length(b)) && !('0' in b) ||
             throw(ArgumentError("The argument given is not a valid Mersenne Number (`M = 2^p - 1`)."))
     end
+    M < 7 && return M == 3
     return ll_primecheck(M)
 end
 

diff --git a/test/runtests.jl b/test/runtests.jl
@@ -239,7 +239,6 @@ end
 # Lucas-Lehmer
 @test !ismersenneprime(2047)
 @test ismersenneprime(8191)
-@test_throws ArgumentError ismersenneprime(3)
 @test_throws ArgumentError ismersenneprime(9)
 @test_throws ismersenneprime(9, check=true)
 # test the following does not throw