From f5b8986681c7c7124a81b1c38ee7673bc863f463 Mon Sep 17 00:00:00 2001
From: NikolajDanger <nikolaj@ingemanngade.net>
Date: Wed, 22 Apr 2026 13:24:55 +0200
Subject: [PATCH] :goat: Compiler fix

---
 centvrion/compiler/runtime/cent_runtime.c | 18 +++++++++++++++---
 tests.py                                  | 13 +++++++++++++
 2 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/centvrion/compiler/runtime/cent_runtime.c b/centvrion/compiler/runtime/cent_runtime.c
index afb9012..936bfe5 100644
--- a/centvrion/compiler/runtime/cent_runtime.c
+++ b/centvrion/compiler/runtime/cent_runtime.c
@@ -380,7 +380,9 @@ static long gcd(long a, long b) {
 static CentValue frac_reduce(long num, long den) {
   if (den < 0) { num = -num; den = -den; }
   long g = gcd(num < 0 ? -num : num, den);
-  return cent_frac(num / g, den / g);
+  num /= g; den /= g;
+  if (den == 1) return cent_int(num);
+  return cent_frac(num, den);
 }
 
 static void to_frac(CentValue v, long *num, long *den) {
@@ -445,11 +447,16 @@ CentValue cent_mul(CentValue a, CentValue b) {
 }
 
 CentValue cent_div(CentValue a, CentValue b) {
+  if (a.type == CENT_NULL) a = cent_int(0);
+  if (b.type == CENT_NULL) b = cent_int(0);
   if (a.type != CENT_INT || b.type != CENT_INT)
     cent_type_error("'/' requires two integers");
   if (b.ival == 0)
     cent_runtime_error("division by zero");
-  return cent_int(a.ival / b.ival);
+  /* floored division (Python // semantics) */
+  long q = a.ival / b.ival;
+  if ((a.ival % b.ival != 0) && ((a.ival < 0) != (b.ival < 0))) q -= 1;
+  return cent_int(q);
 }
 
 CentValue cent_div_frac(CentValue a, CentValue b) {
@@ -460,11 +467,16 @@ CentValue cent_div_frac(CentValue a, CentValue b) {
 }
 
 CentValue cent_mod(CentValue a, CentValue b) {
+  if (a.type == CENT_NULL) a = cent_int(0);
+  if (b.type == CENT_NULL) b = cent_int(0);
   if (a.type != CENT_INT || b.type != CENT_INT)
     cent_type_error("'RELIQVVM' requires two integers");
   if (b.ival == 0)
     cent_runtime_error("modulo by zero");
-  return cent_int(a.ival % b.ival);
+  /* floored modulo (Python % semantics) */
+  long r = a.ival % b.ival;
+  if (r != 0 && ((a.ival < 0) != (b.ival < 0))) r += b.ival;
+  return cent_int(r);
 }
 
 CentValue cent_mod_frac(CentValue a, CentValue b) {
diff --git a/tests.py b/tests.py
index 9e69873..60c1ef3 100644
--- a/tests.py
+++ b/tests.py
@@ -689,6 +689,8 @@ error_tests = [
   ("CVM SVBNVLLA\n[I, II][-I]", CentvrionError),                       # negative index
   ("[I, II][-I]", CentvrionError),                                     # negative value
   ("I / NVLLVS", CentvrionError),                                      # division by zero (NVLLVS coerces to 0)
+  ("V RELIQVVM NVLLVS", CentvrionError),                               # modulo by zero (NVLLVS coerces to 0)
+  ("NVLLVS RELIQVVM NVLLVS", CentvrionError),                          # modulo by zero (both NVLLVS)
   ("I / [I, II]", CentvrionError),                                     # division with array operand
   ("I - \"hello\"", CentvrionError),                                   # subtraction with string
   ("I * \"hello\"", CentvrionError),                                   # multiplication with string
@@ -990,6 +992,17 @@ arithmetic_edge_tests = [
   ("NVLLVS + NVLLVS", Program([], [ExpressionStatement(BinOp(Nullus(), Nullus(), "SYMBOL_PLUS"))]), ValNul()),
   ("NVLLVS - V", Program([], [ExpressionStatement(BinOp(Nullus(), Numeral("V"), "SYMBOL_MINUS"))]), ValInt(-5)),
   ("V - NVLLVS", Program([], [ExpressionStatement(BinOp(Numeral("V"), Nullus(), "SYMBOL_MINUS"))]), ValInt(5)),
+  # NVLLVS coerces to 0 in modulo and division
+  ("NVLLVS RELIQVVM V", Program([], [ExpressionStatement(BinOp(Nullus(), Numeral("V"), "KEYWORD_RELIQVVM"))]), ValInt(0)),
+  ("NVLLVS / V", Program([], [ExpressionStatement(BinOp(Nullus(), Numeral("V"), "SYMBOL_DIVIDE"))]), ValInt(0)),
+  # floored division and modulo with negative operands (Python semantics)
+  ("CVM SVBNVLLA\n- VII RELIQVVM III", Program([ModuleCall("SVBNVLLA")], [ExpressionStatement(BinOp(UnaryMinus(Numeral("VII")), Numeral("III"), "KEYWORD_RELIQVVM"))]), ValInt(2)),
+  ("CVM SVBNVLLA\nVII RELIQVVM - III", Program([ModuleCall("SVBNVLLA")], [ExpressionStatement(BinOp(Numeral("VII"), UnaryMinus(Numeral("III")), "KEYWORD_RELIQVVM"))]), ValInt(-2)),
+  ("CVM SVBNVLLA\n- VII RELIQVVM - III", Program([ModuleCall("SVBNVLLA")], [ExpressionStatement(BinOp(UnaryMinus(Numeral("VII")), UnaryMinus(Numeral("III")), "KEYWORD_RELIQVVM"))]), ValInt(-1)),
+  ("CVM SVBNVLLA\n- VII / III", Program([ModuleCall("SVBNVLLA")], [ExpressionStatement(BinOp(UnaryMinus(Numeral("VII")), Numeral("III"), "SYMBOL_DIVIDE"))]), ValInt(-3)),
+  ("CVM SVBNVLLA\nVII / - III", Program([ModuleCall("SVBNVLLA")], [ExpressionStatement(BinOp(Numeral("VII"), UnaryMinus(Numeral("III")), "SYMBOL_DIVIDE"))]), ValInt(-3)),
+  ("CVM SVBNVLLA\n- VII / - III", Program([ModuleCall("SVBNVLLA")], [ExpressionStatement(BinOp(UnaryMinus(Numeral("VII")), UnaryMinus(Numeral("III")), "SYMBOL_DIVIDE"))]), ValInt(2)),
+  ("CVM SVBNVLLA\n- L RELIQVVM C", Program([ModuleCall("SVBNVLLA")], [ExpressionStatement(BinOp(UnaryMinus(Numeral("L")), Numeral("C"), "KEYWORD_RELIQVVM"))]), ValInt(50)),
 ]
 
 class TestArithmeticEdge(unittest.TestCase):