Add is_prime(char) check to GF(char, k) (#1598)

Nemocas · Dec 18, 2023 · 7761cc1 · 7761cc1
1 parent 209d6b4
commit 7761cc1
Show file tree

Hide file tree

Showing 3 changed files with 19 additions and 3 deletions.
diff --git a/src/flint/FlintTypes.jl b/src/flint/FlintTypes.jl
@@ -2237,7 +2237,9 @@ See [`FqPolyRepField`](@ref) for $p$ being a [`ZZRingElem`](@ref). See [`fqPolyR
    overfields :: Dict{Int, Vector{FinFieldMorphism}}
    subfields :: Dict{Int, Vector{FinFieldMorphism}}
 
-   function fqPolyRepField(c::ZZRingElem, deg::Int, s::Symbol, cached::Bool = true)
+   function fqPolyRepField(c::ZZRingElem, deg::Int, s::Symbol, cached::Bool = true; check::Bool = true)
+      check && !is_prime(c) &&
+         throw(DomainError(c, "the characteristic must be a prime"))
       return get_cached!(FqNmodFiniteFieldID, (c, deg, s), cached) do
          d = new()
          ccall((:fq_nmod_ctx_init, libflint), Nothing,
@@ -2646,7 +2648,9 @@ if NEW_FLINT
      overfields :: Dict{Int, Vector{FinFieldMorphism}}
      subfields :: Dict{Int, Vector{FinFieldMorphism}}
 
-     function FqPolyRepField(char::ZZRingElem, deg::Int, s::Symbol, cached::Bool = true)
+     function FqPolyRepField(char::ZZRingElem, deg::Int, s::Symbol, cached::Bool = true; check::Bool = true)
+        check && !is_probable_prime(char) &&
+          throw(DomainError(char, "the characteristic must be a prime"))
         return get_cached!(FqFiniteFieldID, (char, deg, s), cached) do
            d = new()
            finalizer(_FqFiniteField_clear_fn, d)
@@ -2717,7 +2721,9 @@ else
      overfields :: Dict{Int, Vector{FinFieldMorphism}}
      subfields :: Dict{Int, Vector{FinFieldMorphism}}
 
-     function FqPolyRepField(char::ZZRingElem, deg::Int, s::Symbol, cached::Bool = true)
+     function FqPolyRepField(char::ZZRingElem, deg::Int, s::Symbol, cached::Bool = true; check::Bool = true)
+        check && !is_probable_prime(char) &&
+          throw(DomainError(char, "the characteristic must be a prime"))
         return get_cached!(FqFiniteFieldID, (char, deg, s), cached) do
            d = new()
            finalizer(_FqFiniteField_clear_fn, d)

diff --git a/test/flint/fq-test.jl b/test/flint/fq-test.jl
@@ -258,3 +258,8 @@ end
    R, x = finite_field(ZZ(19), 3, "x")
    @test R([1, 0, 1]) == x^2 + 1
 end
+
+@testset "Nemo.jl#1493" begin
+   @test_throws DomainError GF(ZZ(4), 2)
+   @test_throws DomainError finite_field(ZZ(6), 2, "x")
+end
diff --git a/test/flint/fq_nmod-test.jl b/test/flint/fq_nmod-test.jl
@@ -270,3 +270,8 @@ end
    R, x = finite_field(19, 3, "x")
    @test R([1, 0, 1]) == x^2 + 1
 end
+
+@testset "Nemo.jl#1493" begin
+   @test_throws DomainError GF(4, 2)
+   @test_throws DomainError finite_field(6, 2, "x")
+end