diff --git a/sys/include/unaligned.h b/sys/include/unaligned.h new file mode 100644 index 0000000000000000000000000000000000000000..9dba9ae2fdff94f2252908adc6a1ce5d89e68afc --- /dev/null +++ b/sys/include/unaligned.h @@ -0,0 +1,69 @@ +/* + * Copyright (C) 2019 Kaspar Schleiser <kaspar@schleiser.de> + * + * This file is subject to the terms and conditions of the GNU Lesser + * General Public License v2.1. See the file LICENSE in the top level + * directory for more details. + */ + +/** + * @defgroup sys_unaligned unaligned memory access methods + * @ingroup sys + * @brief Provides functions for safe unaligned memory accesses + * + * This header provides functions to read values from pointers that are not + * necessarily aligned to the type's alignment requirements. + * + * E.g., + * + * uint16_t *foo = 0x123; + * printf("%u\n", *foo); + * + * ... might cause an unaligned access, if `uint16_t` is usually aligned at + * 2-byte-boundaries, as foo has an odd address. + * + * The current implementation casts a pointer to a packed struct, which forces + * the compiler to deal with possibly unalignedness. Idea taken from linux + * kernel sources. + * + * @{ + * + * @file + * @brief Unaligned but safe memory access functions + * + * @author Kaspar Schleiser <kaspar@schleiser.de> + */ + +#ifndef UNALIGNED_H +#define UNALIGNED_H + +#include <stdint.h> + +#ifdef __cplusplus +extern "C" { +#endif + +/** @brief Unaligned access helper struct (uint16_t version) */ +typedef struct __attribute__((packed)) { + uint16_t val; /**< value */ +} uint16_una_t; + +/** + * @brief Get uint16_t from possibly unaligned pointer + * + * @param[in] ptr pointer to read from + * + * @returns value read from @p ptr + */ +static inline uint16_t unaligned_get_u16(const void *ptr) +{ + const uint16_una_t *tmp = ptr; + return tmp->val; +} + +#ifdef __cplusplus +} +#endif + +/** @} */ +#endif /* UNALIGNED_H */