From 2fc39bc868b351fb29d39c2e05edeef6ac09ac12 Mon Sep 17 00:00:00 2001
From: Tommy Hofmann <thofma@gmail.com>
Date: Wed, 8 Jan 2025 21:29:52 +0100
Subject: [PATCH] fix: irreducibility of constant polynomials over finite
 fields

---
 src/flint/fmpz_mod_poly.jl         | 1 +
 src/flint/fq_default_poly.jl       | 1 +
 src/flint/fq_nmod_poly.jl          | 1 +
 src/flint/fq_poly.jl               | 1 +
 src/flint/gfp_fmpz_poly.jl         | 1 +
 src/flint/gfp_poly.jl              | 1 +
 src/flint/nmod_poly.jl             | 1 +
 test/flint/fmpz_mod_poly-test.jl   | 3 +++
 test/flint/fq_default_poly-test.jl | 3 +++
 test/flint/fq_nmod_poly-test.jl    | 3 +++
 test/flint/fq_poly-test.jl         | 3 +++
 test/flint/gfp_fmpz_poly-test.jl   | 3 +++
 test/flint/gfp_poly-test.jl        | 3 +++
 test/flint/nmod_poly-test.jl       | 3 +++
 14 files changed, 28 insertions(+)

diff --git a/src/flint/fmpz_mod_poly.jl b/src/flint/fmpz_mod_poly.jl
index 0658b758ad..58123e64d7 100644
--- a/src/flint/fmpz_mod_poly.jl
+++ b/src/flint/fmpz_mod_poly.jl
@@ -645,6 +645,7 @@ end
 
 function is_irreducible(x::ZZModPolyRingElem)
   !is_probable_prime(modulus(x)) && error("Modulus not prime in is_irreducible")
+  is_constant(x) && return false
   return Bool(@ccall libflint.fmpz_mod_poly_is_irreducible(x::Ref{ZZModPolyRingElem}, x.parent.base_ring.ninv::Ref{fmpz_mod_ctx_struct})::Cint)
 end
 
diff --git a/src/flint/fq_default_poly.jl b/src/flint/fq_default_poly.jl
index 5e6670f245..8e8abc0fad 100644
--- a/src/flint/fq_default_poly.jl
+++ b/src/flint/fq_default_poly.jl
@@ -513,6 +513,7 @@ end
 ################################################################################
 
 function is_irreducible(x::FqPolyRingElem)
+  is_constant(x) && return false
   return Bool(@ccall libflint.fq_default_poly_is_irreducible(x::Ref{FqPolyRingElem}, base_ring(parent(x))::Ref{FqField})::Int32)
 end
 
diff --git a/src/flint/fq_nmod_poly.jl b/src/flint/fq_nmod_poly.jl
index 69c1da09b6..c6e60dddeb 100644
--- a/src/flint/fq_nmod_poly.jl
+++ b/src/flint/fq_nmod_poly.jl
@@ -519,6 +519,7 @@ end
 ################################################################################
 
 function is_irreducible(x::fqPolyRepPolyRingElem)
+  is_constant(x) && return false
   return Bool(@ccall libflint.fq_nmod_poly_is_irreducible(x::Ref{fqPolyRepPolyRingElem}, base_ring(parent(x))::Ref{fqPolyRepField})::Int32)
 end
 
diff --git a/src/flint/fq_poly.jl b/src/flint/fq_poly.jl
index ab033b5dcc..e574060928 100644
--- a/src/flint/fq_poly.jl
+++ b/src/flint/fq_poly.jl
@@ -519,6 +519,7 @@ end
 ################################################################################
 
 function is_irreducible(x::FqPolyRepPolyRingElem)
+  is_constant(x) && return false
   return Bool(@ccall libflint.fq_poly_is_irreducible(x::Ref{FqPolyRepPolyRingElem}, base_ring(parent(x))::Ref{FqPolyRepField})::Int32)
 end
 
diff --git a/src/flint/gfp_fmpz_poly.jl b/src/flint/gfp_fmpz_poly.jl
index 991a7ca2da..456564c1f5 100644
--- a/src/flint/gfp_fmpz_poly.jl
+++ b/src/flint/gfp_fmpz_poly.jl
@@ -242,6 +242,7 @@ end
 ################################################################################
 
 function is_irreducible(x::FpPolyRingElem)
+  is_constant(x) && return false
   return Bool(@ccall libflint.fmpz_mod_poly_is_irreducible(x::Ref{FpPolyRingElem}, x.parent.base_ring.ninv::Ref{fmpz_mod_ctx_struct})::Cint)
 end
 
diff --git a/src/flint/gfp_poly.jl b/src/flint/gfp_poly.jl
index 36d68ce521..0945a49e64 100644
--- a/src/flint/gfp_poly.jl
+++ b/src/flint/gfp_poly.jl
@@ -302,6 +302,7 @@ end
 ################################################################################
 
 function is_irreducible(x::fpPolyRingElem)
+  is_constant(x) && return false
   return Bool(@ccall libflint.nmod_poly_is_irreducible(x::Ref{fpPolyRingElem})::Int32)
 end
 
diff --git a/src/flint/nmod_poly.jl b/src/flint/nmod_poly.jl
index bd4bab902d..677f23571d 100644
--- a/src/flint/nmod_poly.jl
+++ b/src/flint/nmod_poly.jl
@@ -641,6 +641,7 @@ end
 
 function is_irreducible(x::zzModPolyRingElem)
   !is_prime(modulus(x)) && error("Modulus not prime in is_irreducible")
+  is_constant(x) && return false
   return Bool(@ccall libflint.nmod_poly_is_irreducible(x::Ref{zzModPolyRingElem})::Int32)
 end
 
diff --git a/test/flint/fmpz_mod_poly-test.jl b/test/flint/fmpz_mod_poly-test.jl
index c6f8b729c2..6a877662f2 100644
--- a/test/flint/fmpz_mod_poly-test.jl
+++ b/test/flint/fmpz_mod_poly-test.jl
@@ -498,6 +498,9 @@ end
   f = x^2 + 2x + 1
 
   @test is_irreducible(f) == false
+
+  @test !is_irreducible(x^0)
+  @test !is_irreducible(0*x^0)
 end
 
 @testset "ZZModPolyRingElem.is_squarefree" begin
diff --git a/test/flint/fq_default_poly-test.jl b/test/flint/fq_default_poly-test.jl
index 448f6cda2a..720d86a945 100644
--- a/test/flint/fq_default_poly-test.jl
+++ b/test/flint/fq_default_poly-test.jl
@@ -490,6 +490,9 @@ end
   @test is_irreducible(x)
 
   @test is_irreducible(x^16+2*x^9+x^8+x^2+x+1)
+
+  @test !is_irreducible(x^0)
+  @test !is_irreducible(0*x^0)
 end
 
 @testset "FqPolyRingElem.is_squarefree" begin
diff --git a/test/flint/fq_nmod_poly-test.jl b/test/flint/fq_nmod_poly-test.jl
index 4dae83da00..104e35c6cd 100644
--- a/test/flint/fq_nmod_poly-test.jl
+++ b/test/flint/fq_nmod_poly-test.jl
@@ -501,6 +501,9 @@ end
   @test is_irreducible(x)
 
   @test is_irreducible(x^16+2*x^9+x^8+x^2+x+1)
+
+  @test !is_irreducible(x^0)
+  @test !is_irreducible(0*x^0)
 end
 
 @testset "fqPolyRepPolyRingElem.is_squarefree" begin
diff --git a/test/flint/fq_poly-test.jl b/test/flint/fq_poly-test.jl
index 2cd14ee5d5..14e0274eab 100644
--- a/test/flint/fq_poly-test.jl
+++ b/test/flint/fq_poly-test.jl
@@ -502,6 +502,9 @@ end
   @test is_irreducible(x)
 
   @test is_irreducible(x^16+2*x^9+x^8+x^2+x+1)
+
+  @test !is_irreducible(x^0)
+  @test !is_irreducible(0*x^0)
 end
 
 @testset "FqPolyRepPolyRingElem.is_squarefree" begin
diff --git a/test/flint/gfp_fmpz_poly-test.jl b/test/flint/gfp_fmpz_poly-test.jl
index fbbdf4c4e1..bf895af3d0 100644
--- a/test/flint/gfp_fmpz_poly-test.jl
+++ b/test/flint/gfp_fmpz_poly-test.jl
@@ -497,6 +497,9 @@ end
   f = x^2 + 2x + 1
 
   @test is_irreducible(f) == false
+
+  @test !is_irreducible(x^0)
+  @test !is_irreducible(0*x^0)
 end
 
 @testset "FpPolyRingElem.is_squarefree" begin
diff --git a/test/flint/gfp_poly-test.jl b/test/flint/gfp_poly-test.jl
index de0bb91b92..480e4ae839 100644
--- a/test/flint/gfp_poly-test.jl
+++ b/test/flint/gfp_poly-test.jl
@@ -564,6 +564,9 @@ end
   @test is_irreducible(x)
 
   @test is_irreducible(x^16+2*x^9+x^8+x^2+x+1)
+
+  @test !is_irreducible(x^0)
+  @test !is_irreducible(0*x^0)
 end
 
 @testset "fpPolyRingElem.is_squarefree" begin
diff --git a/test/flint/nmod_poly-test.jl b/test/flint/nmod_poly-test.jl
index aa200ea024..e78a6d8b65 100644
--- a/test/flint/nmod_poly-test.jl
+++ b/test/flint/nmod_poly-test.jl
@@ -587,6 +587,9 @@ end
   @test is_irreducible(x)
 
   @test is_irreducible(x^16+2*x^9+x^8+x^2+x+1)
+
+  @test !is_irreducible(x^0)
+  @test !is_irreducible(0*x^0)
 end
 
 @testset "zzModPolyRingElem.is_squarefree" begin