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/*
This file is part of tgl-library
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
Copyright Ben Wiederhake 2015
*/
#ifndef CRYPTO_META_H_
#define CRYPTO_META_H_
#include <assert.h>
/* All this wrapping/unwrapping solves a fundamental problem:
* - The libtgl implementation wants access to the TGLC_* types.
* - The libtgl implementation should not see any other definitions from any
* external crypto library (to make sure no symbol slips "through" during the
* OpenSSL-to-gcrypt transition).
* - Most TGLC_* types (3 out of 4 types) are exclusively used as pointers
* throughout the libtgl source, in a way to allow for incomplete types.
* - The CORE type (e.g. BIGNUM from <openssl/bn.h>) may be incomplete,
* even for tglc.
* This means the standard approaches don't work:
* - TGLC_NAME can't be a typedef to CORE, since CORE shouldn't even be visible
* from libtgl.
* - TGLC_NAME can't be a pointer to CORE, same reason. Also, it would require
* a significant amount of rewriting (error-prone work).
* - TGLC_NAME can't be a void pointer. Retain type checking!
* - So TGLC_NAME *must* be an incomplete custom struct.
* However, this ensues the following ugliness.
*
* The standard doesn't explicitly allow it, but there's a pretty good argument
* that casting ptr-to-some-struct to ptr-to-other-struct is *probably* okay for
* most compilers: https://stackoverflow.com/a/8702750/3070326
*/
#define TGLC_WRAPPER_ASSOC(NAME,CORE) \
static TGLC_ ## NAME *wrap_ ## NAME (const CORE *p) \
__attribute__ ((unused)); \
static CORE *unwrap_ ## NAME (const TGLC_ ## NAME *p) \
__attribute__ ((unused)); \
static CORE *unwrap_ ## NAME (const TGLC_ ## NAME *p) { \
return (CORE *)p; \
} \
static TGLC_ ## NAME *wrap_ ## NAME (const CORE *p) { \
return (TGLC_ ## NAME *)p; \
}
#endif /* CRYPTO_META_H_ */
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