Add (unsigned) remainder (modulus) arithmetic operator bvurem.

Along with tests of its conversion and the function application factory integrity.

Author: NlightNFotis

src/solvers/smt2_incremental/convert_expr_to_smt.cpp

@@ -401,9 +401,22 @@ static smt_termt convert_expr_to_smt(const ieee_float_op_exprt &float_operation)
 
 static smt_termt convert_expr_to_smt(const mod_exprt &truncation_modulo)
 {
-  UNIMPLEMENTED_FEATURE(
-    "Generation of SMT formula for truncation modulo expression: " +
-    truncation_modulo.pretty());
+  const bool both_operands_bitvector =
+    can_cast_type<integer_bitvector_typet>(truncation_modulo.lhs().type()) &&
+    can_cast_type<integer_bitvector_typet>(truncation_modulo.rhs().type());
+
+  if(both_operands_bitvector)
+  {
+    return smt_bit_vector_theoryt::unsigned_remainder(
+      convert_expr_to_smt(truncation_modulo.lhs()),
+      convert_expr_to_smt(truncation_modulo.rhs()));
+  }
+  else
+  {
+    UNIMPLEMENTED_FEATURE(
+      "Generation of SMT formula for remainder (modulus) expression: " +
+      truncation_modulo.pretty());
+  }
 }
 
 static smt_termt

src/solvers/smt2_incremental/smt_bit_vector_theory.cpp

@@ -319,3 +319,26 @@ void smt_bit_vector_theoryt::signed_dividet::validate(
 const smt_function_application_termt::factoryt<
   smt_bit_vector_theoryt::signed_dividet>
   smt_bit_vector_theoryt::signed_divide{};
+
+const char *smt_bit_vector_theoryt::unsigned_remaindert::identifier()
+{
+  return "bvurem";
+}
+
+smt_sortt smt_bit_vector_theoryt::unsigned_remaindert::return_sort(
+  const smt_termt &lhs,
+  const smt_termt &rhs)
+{
+  return lhs.get_sort();
+}
+
+void smt_bit_vector_theoryt::unsigned_remaindert::validate(
+  const smt_termt &lhs,
+  const smt_termt &rhs)
+{
+  validate_bit_vector_predicate_arguments(lhs, rhs);
+}
+
+const smt_function_application_termt::factoryt<
+  smt_bit_vector_theoryt::unsigned_remaindert>
+  smt_bit_vector_theoryt::unsigned_remainder{};

src/solvers/smt2_incremental/smt_bit_vector_theory.h

@@ -126,6 +126,15 @@ class smt_bit_vector_theoryt
   };
   static const smt_function_application_termt::factoryt<signed_dividet>
     signed_divide;
+
+  struct unsigned_remaindert final
+  {
+    static const char *identifier();
+    static smt_sortt return_sort(const smt_termt &lhs, const smt_termt &rhs);
+    static void validate(const smt_termt &lhs, const smt_termt &rhs);
+  };
+  static const smt_function_application_termt::factoryt<unsigned_remaindert>
+    unsigned_remainder;
 };
 
 #endif // CPROVER_SOLVERS_SMT2_INCREMENTAL_SMT_BIT_VECTOR_THEORY_H

unit/solvers/smt2_incremental/convert_expr_to_smt.cpp

@@ -372,4 +372,23 @@ TEST_CASE(
     const cbmc_invariants_should_throwt invariants_throw;
     REQUIRE_THROWS(convert_expr_to_smt(div_exprt{one_bvint, false_exprt{}}));
   }
+
+  SECTION(
+    "Unsigned remainder (modulus) from truncating division of two constant "
+    "size bit-vectors")
+  {
+    const auto constructed_term =
+      convert_expr_to_smt(mod_exprt{one_bvint_unsigned, two_bvint_unsigned});
+    const auto expected_term =
+      smt_bit_vector_theoryt::unsigned_remainder(smt_term_one, smt_term_two);
+    CHECK(constructed_term == expected_term);
+  }
+
+  SECTION(
+    "Ensure that remainder (truncated modulo) node conversion fails if the "
+    "operands are not bit-vector based")
+  {
+    const cbmc_invariants_should_throwt invariants_throw;
+    REQUIRE_THROWS(convert_expr_to_smt(mod_exprt{one_bvint, false_exprt{}}));
+  }
 }

unit/solvers/smt2_incremental/smt_bit_vector_theory.cpp

@@ -269,4 +269,23 @@ TEST_CASE(
     // A division of a bool and a bitvector should hit an invariant violation.
     REQUIRE_THROWS(smt_bit_vector_theoryt::signed_divide(true_val, three));
   }
+
+  SECTION("Unsigned Remainder")
+  {
+    const auto function_application =
+      smt_bit_vector_theoryt::unsigned_remainder(two, three);
+    REQUIRE(
+      function_application.function_identifier() ==
+      smt_identifier_termt("bvurem", smt_bit_vector_sortt{8}));
+    REQUIRE(function_application.get_sort() == smt_bit_vector_sortt{8});
+    REQUIRE(function_application.arguments().size() == 2);
+    REQUIRE(function_application.arguments()[0].get() == two);
+    REQUIRE(function_application.arguments()[1].get() == three);
+
+    cbmc_invariants_should_throwt invariants_throw;
+    // Bit-vectors of mismatched sorts are going to hit an invariant violation.
+    REQUIRE_THROWS(smt_bit_vector_theoryt::unsigned_remainder(three, four));
+    // A remainder of a bool and a bitvector should hit an invariant violation.
+    REQUIRE_THROWS(smt_bit_vector_theoryt::unsigned_remainder(true_val, three));
+  }
 }