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      1 /*
      2  * Copyright 2019-2023 The OpenSSL Project Authors. All Rights Reserved.
      3  *
      4  * Licensed under the Apache License 2.0 (the "License").  You may not use
      5  * this file except in compliance with the License.  You can obtain a copy
      6  * in the file LICENSE in the source distribution or at
      7  * https://www.openssl.org/source/license.html
      8  */
      9 
     10 #ifndef OSSL_INTERNAL_ENDIAN_H
     11 #define OSSL_INTERNAL_ENDIAN_H
     12 #pragma once
     13 
     14 /*
     15  * IS_LITTLE_ENDIAN and IS_BIG_ENDIAN can be used to detect the endianness
     16  * at compile time. To use it, DECLARE_IS_ENDIAN must be used to declare
     17  * a variable.
     18  *
     19  * L_ENDIAN and B_ENDIAN can be used at preprocessor time. They can be set
     20  * in the configarion using the lib_cppflags variable. If neither is
     21  * set, it will fall back to code works with either endianness.
     22  */
     23 
     24 #if defined(__BYTE_ORDER__) && defined(__ORDER_LITTLE_ENDIAN__)
     25 #define DECLARE_IS_ENDIAN const int ossl_is_little_endian = __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
     26 #define IS_LITTLE_ENDIAN (ossl_is_little_endian)
     27 #define IS_BIG_ENDIAN (!ossl_is_little_endian)
     28 #if defined(L_ENDIAN) && (__BYTE_ORDER__ != __ORDER_LITTLE_ENDIAN__)
     29 #error "L_ENDIAN defined on a big endian machine"
     30 #endif
     31 #if defined(B_ENDIAN) && (__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__)
     32 #error "B_ENDIAN defined on a little endian machine"
     33 #endif
     34 #if !defined(L_ENDIAN) && (__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__)
     35 #define L_ENDIAN
     36 #endif
     37 #if !defined(B_ENDIAN) && (__BYTE_ORDER__ != __ORDER_LITTLE_ENDIAN__)
     38 #define B_ENDIAN
     39 #endif
     40 #else
     41 #define DECLARE_IS_ENDIAN \
     42     const union {         \
     43         long one;         \
     44         char little;      \
     45     } ossl_is_endian = { 1 }
     46 
     47 #define IS_LITTLE_ENDIAN (ossl_is_endian.little != 0)
     48 #define IS_BIG_ENDIAN (ossl_is_endian.little == 0)
     49 #endif
     50 
     51 #endif
     52