Hi Jordi,
There is some ARM function you can use.
__REV: Reverses the byte order in unsigned integer value. For example, 0x12345678 becomes 0x78563412.
For example: A=__REV(B); //A,B is 32bit variable
__REVSH: Reverses the byte order in a 16-bit value and returns the signed 16-bit result. For example, 0x0080 becomes 0x8000.
For example: C=__REVSH(D); //C,D is 16bit variable
Regards,
Jing