Add internal MD size getter

Modules / tests that only need to get the size of a hash from its type,
without actually computing a hash, need not depend on MD_C.

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>

library/md_internal.h

@@ -0,0 +1,69 @@
+/**
+ *  Internal MD/hash functions - no crypto, just data.
+ *  This is used to avoid depending on MD_C just to query a length.
+ *
+ *  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_MD_INTERNAL_H
+#define MBEDTLS_MD_INTERNAL_H
+
+#include "common.h"
+
+#include "mbedtls/md.h"
+
+/** Get the output length of the given hash type
+ *
+ * \param md_type   The hash type.
+ *
+ * \return          The output length in bytes, or 0 if not known
+ */
+static inline unsigned char mbedtls_md_internal_get_size( mbedtls_md_type_t md_type )
+{
+    switch( md_type )
+    {
+#if defined(MBEDTLS_MD5_C) || defined(PSA_WANT_ALG_MD5)
+        case MBEDTLS_MD_MD5:
+            return( 16 );
+#endif
+#if defined(MBEDTLS_RIPEMD160_C) || defined(PSA_WANT_ALG_RIPEMD160) || \
+    defined(MBEDTLS_SHA1_C) || defined(PSA_WANT_ALG_SHA_1)
+        case MBEDTLS_MD_RIPEMD160:
+        case MBEDTLS_MD_SHA1:
+            return( 20 );
+#endif
+#if defined(MBEDTLS_SHA224_C) || defined(PSA_WANT_ALG_SHA_224)
+        case MBEDTLS_MD_SHA224:
+            return( 28 );
+#endif
+#if defined(MBEDTLS_SHA256_C) || defined(PSA_WANT_ALG_SHA_256)
+        case MBEDTLS_MD_SHA256:
+            return( 32 );
+#endif
+#if defined(MBEDTLS_SHA384_C) || defined(PSA_WANT_ALG_SHA_384)
+        case MBEDTLS_MD_SHA384:
+            return( 48 );
+#endif
+#if defined(MBEDTLS_SHA512_C) || defined(PSA_WANT_ALG_SHA_512)
+        case MBEDTLS_MD_SHA512:
+            return( 64 );
+#endif
+        default:
+            return( 0 );
+    }
+}
+
+#endif /* MBEDTLS_MD_INTERNAL_H */