From be48dbf90bcf43831a0716fb300a59fb9f3e84d8 Mon Sep 17 00:00:00 2001
From: Tommy Hofmann <thofma@gmail.com>
Date: Mon, 6 Jan 2025 20:04:35 +0100
Subject: [PATCH 1/2] fix: make invmod more robust for non-prime moduli (#1986)

(before it was giving silently wrong results)
---
 src/HeckeMoreStuff.jl            | 3 ++-
 test/flint/fmpz_mod_poly-test.jl | 6 ++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/HeckeMoreStuff.jl b/src/HeckeMoreStuff.jl
index 994514333b..7abe92c401 100644
--- a/src/HeckeMoreStuff.jl
+++ b/src/HeckeMoreStuff.jl
@@ -400,7 +400,8 @@ end
 function invmod(f::ZZModPolyRingElem, M::ZZModPolyRingElem)
   if !is_unit(f)
     r = parent(f)()
-    i = @ccall libflint.fmpz_mod_poly_invmod(r::Ref{ZZModPolyRingElem}, f::Ref{ZZModPolyRingElem}, M::Ref{ZZModPolyRingElem}, f.parent.base_ring.ninv::Ref{fmpz_mod_ctx_struct})::Int
+    ff = ZZ()
+    i = @ccall libflint.fmpz_mod_poly_invmod_f(ff::Ref{ZZRingElem}, r::Ref{ZZModPolyRingElem}, f::Ref{ZZModPolyRingElem}, M::Ref{ZZModPolyRingElem}, f.parent.base_ring.ninv::Ref{fmpz_mod_ctx_struct})::Int
     if iszero(i)
       error("not yet implemented")
     else
diff --git a/test/flint/fmpz_mod_poly-test.jl b/test/flint/fmpz_mod_poly-test.jl
index b4db6f5776..c6f8b729c2 100644
--- a/test/flint/fmpz_mod_poly-test.jl
+++ b/test/flint/fmpz_mod_poly-test.jl
@@ -343,6 +343,12 @@ end
   @test powermod(f, -10, g) == 78305338116088931412*x+91239060941924718463
 
   @test powermod(f, -ZZRingElem(10), g) == 78305338116088931412*x+91239060941924718463
+
+  R, = residue_ring(ZZ, ZZ(2809))
+  Rx, x = R[:x]
+  f = 32*x^9 + 28*x^8 + 2497*x^7 + 2443*x^6 + 708*x^5 + 996*x^4 + 2557*x^3 + 2104*x^2 + 2517*x + 2752
+  g = x^10 + 2798*x^8 + 2806*x^7 + 37*x^6 + 14*x^5 + 2761*x^4 + 2787*x^3 + 20*x^2 + 12*x + 1
+  @test_throws ErrorException invmod(f, g)
 end
 
 @testset "ZZModPolyRingElem.euclidean_division" begin

From fc77b13721c353d8d8b6682e749f65381e1458f2 Mon Sep 17 00:00:00 2001
From: Tommy Hofmann <thofma@gmail.com>
Date: Tue, 7 Jan 2025 18:31:51 +0100
Subject: [PATCH 2/2] fix: aliasing bug in mul! (#1987)

---
 src/flint/gfp_fmpz_elem.jl  | 11 +++++++----
 test/flint/gfp_fmpz-test.jl |  7 +++++++
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/src/flint/gfp_fmpz_elem.jl b/src/flint/gfp_fmpz_elem.jl
index d4fa418d72..7a89b1117f 100644
--- a/src/flint/gfp_fmpz_elem.jl
+++ b/src/flint/gfp_fmpz_elem.jl
@@ -364,10 +364,13 @@ end
 
 function mul!(z::FpFieldElem, x::FpFieldElem, y::ZZRingElem)
   R = parent(x)
-  @ccall libflint.fmpz_mod(z.data::Ref{ZZRingElem}, y::Ref{ZZRingElem}, R.n::Ref{ZZRingElem})::Nothing
-
-  @ccall libflint.fmpz_mod_mul(z.data::Ref{ZZRingElem}, x.data::Ref{ZZRingElem}, z.data::Ref{ZZRingElem}, R.ninv::Ref{fmpz_mod_ctx_struct})::Nothing
-  return z
+  if z !== x
+    @ccall libflint.fmpz_mod(z.data::Ref{ZZRingElem}, y::Ref{ZZRingElem}, R.n::Ref{ZZRingElem})::Nothing
+    @ccall libflint.fmpz_mod_mul(z.data::Ref{ZZRingElem}, x.data::Ref{ZZRingElem}, z.data::Ref{ZZRingElem}, R.ninv::Ref{fmpz_mod_ctx_struct})::Nothing
+    return z
+  else
+    return mul!(z, x, R(y))
+  end
 end
 
 function add!(z::FpFieldElem, x::FpFieldElem, y::FpFieldElem)
diff --git a/test/flint/gfp_fmpz-test.jl b/test/flint/gfp_fmpz-test.jl
index 1216be268e..29c1b418f8 100644
--- a/test/flint/gfp_fmpz-test.jl
+++ b/test/flint/gfp_fmpz-test.jl
@@ -532,3 +532,10 @@ end
   R = Native.GF(ZZ(19))
   @test R([5]) == R(5)
 end
+
+@testset "gfp_fmpz.bug" begin
+  R = Native.GF(ZZRingElem(123456789012345678949))
+  z = R(1)
+  mul!(z, z, ZZ(10))
+  @test z == 10
+end