/*
> To: Jim Gettys <jg@pa.dec.com>
> Cc: gnome-list@gnome.org
> Subject: Re: Milestones document
> -----
> On Wed, 8 Dec 1999, Jim Gettys wrote:
> 
> > For example, the next time you break library binary compatibility, you
> > go through all data structures and sort the structure elements small to
> > large, (often with subunits of information that ought to be local in a
> > cache line)
> 
> Small to large or large to small? (Or does it make a diff as long as it is
> sorted?)

Small to large: all C compilers in the world lay out memory in the order
of declaration, and they keep data naturally aligned.  This is universally
true.  While vital on a RISC, CISC's like an x86, while not causing a trap,
will take a significant performance hit on unaligned data, so compilers
have kept data naturally aligned by default for a long time (even a VAX
took a significant performance hit if the data wasn't aligned, and it has
gotten amazingrly worse as processors have gotten faster (and more RISC
like internally on CISC machines).

Example program length.c:
*/

#include <stdio.h>

typedef struct _foo {
  char character4;
  char *pointer;
  short integer;
  char *pointer2;
  char character2;
} foostruct;

typedef struct _foo2 {
  char character;
  char character2;
  short integer;
  char *pointer;
  char *pointer2;
} foostruct2;

main()
{
  printf("size = %d, %d\n", sizeof(foostruct), sizeof(foostruct2));
  exit();
}


/*
[jg@jg jg]$ ./length
size = 20, 12
*/