All data items are held in the native byte order of the MSP430 processor. The plain character type is signed by default. The floating-point types float and double are implemented as 32-bit and 64-bit IEEE floating-point.

Data Type	Size in bytes	Alignment in bytes
char, signed char, and unsigned char	1	1
int and unsigned int	2	2
short and unsigned short	2	2
long and unsigned long	4	2
long long and unsigned long long	8	2
float and double (compiled with -msd)	4	2
double and long double	8	2
type * (pointer)	2	2
enum (enumeration)	2	2

When compiling for the MSP430X in the 1MB addressing mode using -m1m, function pointers are still represented in a 16-bit pointer but are ‘thunked’. That is, the compiler uses an indirect call through the 16-bit address to anywhere in the 20-bit address range.

As a C programmer this has no impact on the way that you write your code, but if you are passing function pointers to assembly code or are dealing with function pointers at a low-level, such as porting an RTOS, then you need to be aware that function pointers are not held as 20-bit addresses.