Use macro guard for function declaration

Signed-off-by: Gabor Mezei <[email protected]>

library/ecp_invasive.h

@@ -169,6 +169,17 @@ int  mbedtls_ecp_mod_p384_raw(mbedtls_mpi_uint *X, size_t X_limbs);
 
 #endif /* MBEDTLS_ECP_DP_SECP384R1_ENABLED */
 
+#if defined(MBEDTLS_ECP_DP_SECP192K1_ENABLED)
+
+/*
+ * Fast quasi-reduction modulo p192k1 = 2^192 - R,
+ * with R = 2^32 + 2^12 + 2^8 + 2^7 + 2^6 + 2^3 + 1 = 0x0100001119
+ */
+MBEDTLS_STATIC_TESTABLE
+int mbedtls_ecp_mod_p192k1(mbedtls_mpi *N);
+
+#endif /* MBEDTLS_ECP_DP_SECP192K1_ENABLED */
+
 /** Initialise a modulus with hard-coded const curve data.
  *
  * \note            The caller is responsible for the \p N modulus' memory.
@@ -191,9 +202,6 @@ int mbedtls_ecp_modulus_setup(mbedtls_mpi_mod_modulus *N,
                               const mbedtls_ecp_group_id id,
                               const mbedtls_ecp_curve_type ctype);
 
-MBEDTLS_STATIC_TESTABLE
-int mbedtls_ecp_mod_p192k1(mbedtls_mpi *N);
-
 #endif /* MBEDTLS_TEST_HOOKS && MBEDTLS_ECP_C */
 
 #endif /* MBEDTLS_ECP_INVASIVE_H */