Implementation Differences

Implementation Differences

This section lists differences between the 32-bit and the 64-bit C implementations. Because all of the implementations adhere to the ANSI standard, and because C is a rigorously defined language designed to be portable, only a few differences exist between the 32-bit, n32, and 64-bit compiler implementations. The areas where differences can occur are in data types (by definition) and in areas where ANSI does not define the precise behavior of the language. In this area the n32 ABI is like the current 32-bit ABI. Thus, it is easier to port to the n32 ABI than to the 64-bit ABI.

Table 2-3 summarizes the differences in data types under the 32-bit and 64-bit data type models.

Differences in Data Type Sizes
C type 32-bit and N32 64-bit
char 8 8
short int 16 16
int 32 32
long int 32 64
long long int 64 64
pointer 32 64
float 32 32
double 64 64
long double[1] 64 (128 in n32) 128

Differences in Data Type Sizes
C type	32-bit and N32	64-bit
char	8	8
short int	16	16
int	32	32
long int	32	64
long long int	64	64
pointer	32	64
float	32	32
double	64	64
long double[1]	64 (128 in n32)	128

As you can see in Table 2-3, long ints, pointers, and long doubles are different under the two models.

[1] On ucode 32-bit compiles the long double data type generates a warning message indicating that the long qualifier is not supported. It is supported under n32.