fsfw/serialize/EndianConverter.h

125 lines
3.6 KiB
C++

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