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Re: [PATCH] Reduce memory required by build_string


On Mon, Jun 26, 2006 at 01:58:30PM +0200, Richard Guenther wrote:
> 2006-06-26  Richard Guenther  <rguenther@suse.de>
> 
> 	* tree.c (build_string): Do not waste tail padding in
> 	struct tree_string.
> 
> Index: tree.c
> ===================================================================
> *** tree.c	(revision 115006)
> --- tree.c	(working copy)
> *************** build_string (int len, const char *str)
> *** 1120,1127 ****
>   {
>     tree s;
>     size_t length;
> !   
> !   length = len + sizeof (struct tree_string);
>   
>   #ifdef GATHER_STATISTICS
>     tree_node_counts[(int) c_kind]++;
> --- 1120,1130 ----
>   {
>     tree s;
>     size_t length;
> ! 
> !   /* Do not waste bytes provided by padding of struct tree_string.  */
> !   length = ((len + sizeof (struct tree_string))
> ! 	    & ~(sizeof (struct tree_string)
> ! 		- offsetof (struct tree_string, str) - 1));

How do you know that sizeof (struct tree_string) - offsetof (struct tree_string, str)
is a power of two?

I think
  length = len + offsetof (struct tree_string, str);
would be much better.

	Jakub


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