121 lines
3.7 KiB
C++
121 lines
3.7 KiB
C++
#ifndef FSFW_SERIALIZE_ENDIANCONVERTER_H_
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#define FSFW_SERIALIZE_ENDIANCONVERTER_H_
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#include <cstdint>
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#include <cstring>
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#include "fsfw/osal/Endiness.h"
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/**
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* Helper class to convert variables or bitstreams between machine
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* endian and either big or little endian.
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* Machine endian is the endianness used by the machine running the
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* program and is one of big or little endian. As this is portable
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* code, it is not known at coding time which it is. At compile time
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* it is however, which is why this is implemented using compiler
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* macros and translates to a copy operation at runtime.
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*
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* This changes the layout of multi-byte variables in the machine's
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* memory. In most cases, you should not need to use this class.
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* Probably what you are looking for is the SerializeAdapter.
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* If you still decide you need this class, please read and understand
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* the code first.
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*
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* The order of the individual bytes of the multi-byte variable is
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* reversed, the byte at the highest address is moved to the lowest
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* address and vice versa, same for the bytes in between.
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*
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* Note that the conversion is also its inversion, that is converting
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* from machine to a specified endianness is the same operation as
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* converting from specified to machine (I looked it up, mathematicians
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* would call it an involution):
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*
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* X == convertBigEndian(convertBigEndian(X))
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*
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* Thus, there is only one function supplied to do the conversion.
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*/
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class EndianConverter {
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private:
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EndianConverter() = default;
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public:
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/**
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* Convert a typed variable between big endian and machine endian.
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* Intended for plain old datatypes.
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*/
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template <typename T>
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static T convertBigEndian(T in) {
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#ifndef BYTE_ORDER_SYSTEM
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#error BYTE_ORDER_SYSTEM not defined
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#elif BYTE_ORDER_SYSTEM == LITTLE_ENDIAN
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T tmp;
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auto *pointerOut = reinterpret_cast<uint8_t *>(&tmp);
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auto *pointerIn = reinterpret_cast<uint8_t *>(&in);
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for (size_t count = 0; count < sizeof(T); count++) {
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pointerOut[sizeof(T) - count - 1] = pointerIn[count];
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}
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return tmp;
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#elif BYTE_ORDER_SYSTEM == BIG_ENDIAN
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return in;
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#else
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#error Unknown Byte Order
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#endif
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}
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/**
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* convert a bytestream representing a single variable between big endian
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* and machine endian.
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*/
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static void convertBigEndian(uint8_t *out, const uint8_t *in, size_t size) {
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#ifndef BYTE_ORDER_SYSTEM
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#error BYTE_ORDER_SYSTEM not defined
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#elif BYTE_ORDER_SYSTEM == LITTLE_ENDIAN
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for (size_t count = 0; count < size; count++) {
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out[size - count - 1] = in[count];
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}
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#elif BYTE_ORDER_SYSTEM == BIG_ENDIAN
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memcpy(out, in, size);
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#endif
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}
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/**
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* Convert a typed variable between little endian and machine endian.
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* Intended for plain old datatypes.
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*/
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template <typename T>
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static T convertLittleEndian(T in) {
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#ifndef BYTE_ORDER_SYSTEM
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#error BYTE_ORDER_SYSTEM not defined
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#elif BYTE_ORDER_SYSTEM == BIG_ENDIAN
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T tmp;
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auto *pointerOut = reinterpret_cast<uint8_t *>(&tmp);
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auto *pointerIn = reinterpret_cast<uint8_t *>(&in);
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for (size_t count = 0; count < sizeof(T); count++) {
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pointerOut[sizeof(T) - count - 1] = pointerIn[count];
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}
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return tmp;
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#elif BYTE_ORDER_SYSTEM == LITTLE_ENDIAN
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return in;
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#else
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#error Unknown Byte Order
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#endif
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}
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/**
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* convert a bytestream representing a single variable between little endian
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* and machine endian.
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*/
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static void convertLittleEndian(uint8_t *out, const uint8_t *in, size_t size) {
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#ifndef BYTE_ORDER_SYSTEM
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#error BYTE_ORDER_SYSTEM not defined
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#elif BYTE_ORDER_SYSTEM == BIG_ENDIAN
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for (size_t count = 0; count < size; count++) {
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out[size - count - 1] = in[count];
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}
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#elif BYTE_ORDER_SYSTEM == LITTLE_ENDIAN
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memcpy(out, in, size);
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#endif
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}
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};
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#endif /* FSFW_SERIALIZE_ENDIANCONVERTER_H_ */
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