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Next: Porting Considerations Up: Note 227: 64-Bit Compiler Considerations Previous: Contents

Subsections

Introduction

Motivation

To take advantage of large memory machines available at the NCSA we need to move beyond 32-bit pointers because they limit the amount of memory to 1 Gb. Additionally, with a 64bit Linux and the IA64 Intel processor series on the horizon, it behooves us to be fully "64-bit" clean sooner rather than later. AIPS++ already has working 64-bit builds on the Dec Alpha and SGI Origin series using architecture-specific #ifdef macros (e.g. __alpha or _sgi*) to handle the critical 64-bit differences. All 64-bit differences have not been addressed throughout the library, however, and we need to define coding rules and conventions for this purpose. They may be implemented incrementally however.

Background

Here's a table lifted from the "SGI MIPSpro 64-bit Porting and Transition Guide". It shows how long each of the types are in bits. Note that longs and pointers have different sizes depending on compiling using 64- or 32-bit modes.

C type 32-bit 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 64 128

Next: Porting Considerations Up: Note 227: 64-Bit Compiler Considerations Previous: Contents Contents

C type	32-bit	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	64	128