Add quasi-reduction function for ecp
Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>
diff --git a/library/ecp.c b/library/ecp.c
index d9d5425..835bfa3 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -79,6 +79,8 @@
#include "bn_mul.h"
#include "ecp_invasive.h"
+#include "ecp_internal.h"
+#include "bignum_core.h"
#include <string.h>
@@ -1029,6 +1031,20 @@
return ret;
}
+int mbedtls_ecp_quasi_reduction(mbedtls_mpi_uint *X,
+ const mbedtls_mpi_mod_modulus *N)
+{
+ if (N->limbs == 0) {
+ return MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
+ }
+
+ mbedtls_mpi_uint c = mbedtls_mpi_core_sub(X, X, N->p, N->limbs);
+
+ (void) mbedtls_mpi_core_add_if(X, N->p, N->limbs, (unsigned) c);
+
+ return 0;
+}
+
/*
* Fast mod-p functions expect their argument to be in the 0..p^2 range.
*
diff --git a/library/ecp_internal.h b/library/ecp_internal.h
new file mode 100644
index 0000000..07bf386
--- /dev/null
+++ b/library/ecp_internal.h
@@ -0,0 +1,34 @@
+/**
+ * \file ecp_internal.h
+ *
+ * \brief Function declarations for internal functions of elliptic curve
+ * point arithmetic.
+ */
+/**
+ * Copyright The Mbed TLS Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef MBEDTLS_ECP_INTERNAL_H
+#define MBEDTLS_ECP_INTERNAL_H
+
+#include "common.h"
+#include "mbedtls/bignum.h"
+#include "bignum_mod.h"
+
+int mbedtls_ecp_quasi_reduction(mbedtls_mpi_uint *X,
+ const mbedtls_mpi_mod_modulus *N);
+
+#endif /* MBEDTLS_ECP_INTERNAL_H */