5.6 Data Types

Table 5-1 lists the size, representation, and range of each scalar data type for the MSP430 compiler. Many of the range values are available as standard macros in the header file limits.h.

The storage and alignment of data types is described in Section 6.2.

Table 5-1 MSP430 C/C++ Data Types

				Range
Type	Size	Alignment	Representation	Minimum	Maximum
signed char	8 bits	8	Binary	-128	127
char	8 bits	8	ASCII	0 or -128 ⁽¹⁾	255 or 127 ⁽¹⁾
unsigned char	8 bits	8	Binary	0	255
bool (C99)	8 bits	8	Binary	0 (false)	1 (true)
_Bool (C99)	8 bits	8	Binary	0 (false)	1 (true)
bool (C++)	8 bits	8	Binary	0 (false)	1 (true)
short, signed short	16 bits	16	Binary	-32 768	32 767
unsigned short	16 bits	16	Binary	0	65 535
int, signed int	16 bits	16	Binary	-32 768	32 767
unsigned int	16 bits	16	Binary	0	65 535
long, signed long	32 bits	16	Binary	-2 147 483 648	2 147 483 647
unsigned long	32 bits	16	Binary	0	4 294 967 295
long long, signed long long	64 bits	16	Binary	-9 223 372 036 854 775 808	9 223 372 036 854 775 807
unsigned long long	64 bits	16	Binary	0	18 446 744 073 709 551 615
enum	varies ⁽²⁾	16	Binary	varies	varies
float	32 bits	16	IEEE 32-bit	1.175 494e-38⁽³⁾	3.40 282 346e+38
double	64 bits	16	IEEE 64-bit	2.22 507 385e-308⁽³⁾	1.79 769 313e+308
long double	64 bits	16	IEEE 64-bit	2.22 507 385e-308⁽³⁾	1.79 769 313e+308
function and data pointers	varies (see Table 5-2)	16

(1) "Plain" char has the same representation as either signed char or unsigned char. The --plain_char option specifies whether "plain" char is signed or unsigned. The default is unsigned.

(2) For details about the size of an enum type, see Section 5.6.1.

(3) Figures are minimum precision.

The char type is unsigned by default. This is in contrast to the "signed char" and "unsigned char" types, which specify their sign behavior. You can change the default for the "char" type using the --plain_char=signed compiler option.

Negative values for signed types are represented using two's complement.

The additional types from C, C99 and C++ are defined as synonyms for standard types:

    typedef unsigned int     wchar_t;
    typedef unsigned int     wint_t;

MSP devices support multiple data and code memory models. The code and data model affects the size, alignment, and storage space used for function pointers, data pointers, the size_t type, and the ptrdiff_t type. Pointers with sizes that are not a power of 2 are always stored in a container with a size of a power of 2 bits. That is, 20-bit types are stored in 32 bits.

Table 5-2 Data Sizes for MSP430 Pointers

Code or Data Model	Type	Size	Storage	Alignment
small code model	function pointer	16	16	16
large code model	function pointer	20	32	16

small data model	data pointer	16	16	16
small data model	size_t	16	16	16
small data model	ptrdiff_t	16	16	16

restricted data model	data pointer	20	32	16
restricted data model	size_t	16	16	16
restricted data model	ptrdiff_t	16	16	16

large data model ⁽¹⁾	data pointer	20	32	16
large data model	size_t	32	32	16
large data model	ptrdiff_t	32	32	16

(1) MSP430X large-data model is specified by --silicon_version=mspx --data_model=large