From 14c1be8704a70e3618ae2d11443b5eb4da3aedac Mon Sep 17 00:00:00 2001
From: Tommy Hofmann <thofma@gmail.com>
Date: Sun, 24 Nov 2024 19:42:47 +0100
Subject: [PATCH] fix: nmod_mpoly with modulus 1

---
 src/nmod_mpoly/gen.c        | 6 ++++++
 src/nmod_mpoly/is_gen.c     | 3 +++
 src/nmod_mpoly/test/t-gen.c | 2 +-
 3 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/nmod_mpoly/gen.c b/src/nmod_mpoly/gen.c
index b7c3d209ef..9d65a84559 100644
--- a/src/nmod_mpoly/gen.c
+++ b/src/nmod_mpoly/gen.c
@@ -16,6 +16,12 @@ void nmod_mpoly_gen(nmod_mpoly_t A, slong var, const nmod_mpoly_ctx_t ctx)
 {
     flint_bitcnt_t bits;
 
+    if (ctx->mod.n == UWORD(1))
+    {
+        nmod_mpoly_zero(A, ctx);
+        return;
+    }
+
     bits = mpoly_gen_bits_required(var, ctx->minfo);
     bits = mpoly_fix_bits(bits, ctx->minfo);
     nmod_mpoly_fit_length_reset_bits(A, 1, bits, ctx);
diff --git a/src/nmod_mpoly/is_gen.c b/src/nmod_mpoly/is_gen.c
index daab1cbf43..f5fae4e260 100644
--- a/src/nmod_mpoly/is_gen.c
+++ b/src/nmod_mpoly/is_gen.c
@@ -15,6 +15,9 @@
 int nmod_mpoly_is_gen(const nmod_mpoly_t A,
                                          slong var, const nmod_mpoly_ctx_t ctx)
 {
+    if (ctx->mod.n == UWORD(1))
+        return 1;
+
     if (A->length != WORD(1))
         return 0;
 
diff --git a/src/nmod_mpoly/test/t-gen.c b/src/nmod_mpoly/test/t-gen.c
index e74d86de6c..1f29ac5f09 100644
--- a/src/nmod_mpoly/test/t-gen.c
+++ b/src/nmod_mpoly/test/t-gen.c
@@ -23,7 +23,7 @@ TEST_FUNCTION_START(nmod_mpoly_gen, state)
         slong len, exp_bits, k1, k2;
         ulong modulus;
 
-        modulus = UWORD(2) + n_randint(state, -UWORD(2));
+        modulus = UWORD(1) + n_randint(state, -UWORD(2));
         nmod_mpoly_ctx_init_rand(ctx, state, 20, modulus);
         if (ctx->minfo->nvars < 1)
         {