Move bignum flag for negative zero into test_info

Add accessors ready for protection with test_info mutex.

Signed-off-by: Paul Elliott <paul.elliott@arm.com>

tests/include/test/bignum_helpers.h

@@ -77,30 +77,22 @@ void mbedtls_test_mpi_mod_modulus_free_with_limbs(mbedtls_mpi_mod_modulus *N);
  *
  * - This function guarantees that if \p s begins with '-' then the sign
  *   bit of the result will be negative, even if the value is 0.
- *   When this function encounters such a "negative 0", it
+ *   When this function encounters such a "negative 0", it calls
- *   increments #mbedtls_test_case_uses_negative_0.
+ *   mbedtls_test_increment_case_uses_negative_0().
- * - The size of the result is exactly the minimum number of limbs needed
+ * - The size of the result is exactly the minimum number of limbs needed to fit
- *   to fit the digits in the input. In particular, this function constructs
+ *   the digits in the input. In particular, this function constructs a bignum
- *   a bignum with 0 limbs for an empty string, and a bignum with leading 0
+ *   with 0 limbs for an empty string, and a bignum with leading 0 limbs if the
- *   limbs if the string has sufficiently many leading 0 digits.
+ *   string has sufficiently many leading 0 digits. This is important so that
- *   This is important so that the "0 (null)" and "0 (1 limb)" and
+ *   the "0 (null)" and "0 (1 limb)" and "leading zeros" test cases do what they
- *   "leading zeros" test cases do what they claim.
+ *   claim.
  *
- * \param[out] X        The MPI object to populate. It must be initialized.
+ * \param[out] X The MPI object to populate. It must be initialized.
- * \param[in] s         The null-terminated hexadecimal string to read from.
+ * \param[in] s The null-terminated hexadecimal string to read from.
  *
  * \return \c 0 on success, an \c MBEDTLS_ERR_MPI_xxx error code otherwise.
  */
 int mbedtls_test_read_mpi(mbedtls_mpi *X, const char *s);
 
-/** Nonzero if the current test case had an input parsed with
- * mbedtls_test_read_mpi() that is a negative 0 (`"-"`, `"-0"`, `"-00"`, etc.,
- * constructing a result with the sign bit set to -1 and the value being
- * all-limbs-0, which is not a valid representation in #mbedtls_mpi but is
- * tested for robustness).
- */
-extern unsigned mbedtls_test_case_uses_negative_0;
-
 #endif /* MBEDTLS_BIGNUM_C */
 
 #endif /* TEST_BIGNUM_HELPERS_H */

tests/include/test/helpers.h

@@ -74,6 +74,9 @@ typedef struct {
 #if defined(MBEDTLS_TEST_MUTEX_USAGE)
     const char *mutex_usage_error;
 #endif
+#if defined(MBEDTLS_BIGNUM_C)
+    unsigned case_uses_negative_0;
+#endif
 }
 mbedtls_test_info_t;
 
@@ -151,6 +154,28 @@ const char *mbedtls_test_get_mutex_usage_error(void);
 void mbedtls_test_set_mutex_usage_error(const char *msg);
 #endif
 
+#if defined(MBEDTLS_BIGNUM_C)
+
+/**
+ * \brief           Get whether the current test is a bignum test that uses
+ *                  negative zero.
+ *
+ * \return          non zero if the current test uses bignum negative zero.
+ */
+unsigned mbedtls_test_get_case_uses_negative_0(void);
+
+/**
+ * \brief           Indicate that the current test uses bignum negative zero.
+ *
+ * \note            This function is called if the current test case had an
+ *                  input parsed with mbedtls_test_read_mpi() that is a negative
+ *                  0 (`"-"`, `"-0"`, `"-00"`, etc., constructing a result with
+ *                  the sign bit set to -1 and the value being all-limbs-0,
+ *                  which is not a valid representation in #mbedtls_mpi but is
+ *                  tested for robustness). *
+ */
+void  mbedtls_test_increment_case_uses_negative_0(void);
+#endif
 
 int mbedtls_test_platform_setup(void);
 void mbedtls_test_platform_teardown(void);

tests/src/bignum_helpers.c

@@ -135,7 +135,7 @@ int mbedtls_test_read_mpi(mbedtls_mpi *X, const char *s)
     }
     if (negative) {
         if (mbedtls_mpi_cmp_int(X, 0) == 0) {
-            ++mbedtls_test_case_uses_negative_0;
+            mbedtls_test_increment_case_uses_negative_0();
         }
         X->s = -1;
     }

tests/src/helpers.c

@@ -109,6 +109,25 @@ void mbedtls_test_set_mutex_usage_error(const char *msg)
 }
 #endif // #if defined(MBEDTLS_TEST_MUTEX_USAGE)
 
+#if defined(MBEDTLS_BIGNUM_C)
+
+unsigned mbedtls_test_get_case_uses_negative_0(void)
+{
+    return mbedtls_test_info.case_uses_negative_0;
+}
+
+void mbedtls_test_set_case_uses_negative_0(unsigned uses)
+{
+    mbedtls_test_info.case_uses_negative_0 = uses;
+}
+
+void mbedtls_test_increment_case_uses_negative_0(void)
+{
+    ++mbedtls_test_info.case_uses_negative_0;
+}
+
+#endif
+
 /*----------------------------------------------------------------------------*/
 /* Helper Functions */
 
@@ -171,10 +190,6 @@ void mbedtls_test_skip(const char *test, int line_no, const char *filename)
     mbedtls_test_set_result(MBEDTLS_TEST_RESULT_SKIPPED, test, line_no, filename);
 }
 
-#if defined(MBEDTLS_BIGNUM_C)
-unsigned mbedtls_test_case_uses_negative_0 = 0;
-#endif
-
 void mbedtls_test_info_reset(void)
 {
     mbedtls_test_set_result(MBEDTLS_TEST_RESULT_SUCCESS, 0, 0, 0);
@@ -183,7 +198,7 @@ void mbedtls_test_info_reset(void)
     mbedtls_test_set_line2(NULL);
 
 #if defined(MBEDTLS_BIGNUM_C)
-    mbedtls_test_case_uses_negative_0 = 0;
+    mbedtls_test_set_case_uses_negative_0(0);
 #endif
 }
 

tests/suites/test_suite_bignum.function

@@ -24,7 +24,7 @@ static int sign_is_valid(const mbedtls_mpi *X)
      * we sometimes test the robustness of library functions when given
      * a negative zero input. If a test case has a negative zero as input,
      * we don't mind if the function has a negative zero output. */
-    if (!mbedtls_test_case_uses_negative_0 &&
+    if (!mbedtls_test_get_case_uses_negative_0() &&
         mbedtls_mpi_bitlen(X) == 0 && X->s != 1) {
         return 0;
     }