Subject: Re: [RFT] fib_trie: macro cleanup

From: Andrew Morton <[email-masked]>
Date: Thu, 26 Jul 2007 03:54:33 -0700

On Thu, 26 Jul 2007 11:43:34 +0100 Stephen Hemminger <[email-masked]> wrote:

> This patch converts the messy macro for MASK_PFX to inline function
> and expands TKEY_GET_MASK in the one place it is used.
> 
> 
> --- a/net/ipv4/fib_trie.c	2007-07-26 09:26:19.000000000 +0100
> +++ b/net/ipv4/fib_trie.c	2007-07-26 10:17:21.000000000 +0100
> @@ -85,8 +85,6 @@
>  #define MAX_STAT_DEPTH 32
>  
>  #define KEYLENGTH (8*sizeof(t_key))
> -#define MASK_PFX(k, l) (((l)==0)?0:(k >> (KEYLENGTH-l)) << (KEYLENGTH-l))
> -#define TKEY_GET_MASK(offset, bits) (((bits)==0)?0:((t_key)(-1) << (KEYLENGTH - bits) >> offset))
>  
>  typedef unsigned int t_key;
>  
> @@ -192,6 +190,11 @@ static inline int tnode_child_length(con
>  	return 1 << tn->bits;
>  }
>  
> +static inline t_key mask_pfx(t_key k, unsigned short l)
> +{
> +	return (l == 0) ? 0 : k >> (KEYLENGTH-l) << (KEYLENGTH-l);
> +}

that's a funy way of doing the masking, isn't it?  I suppose gcc will turn
it into the single and-immediate.

>  static inline t_key tkey_extract_bits(t_key a, int offset, int bits)
>  {
>  	if (offset < KEYLENGTH)
> @@ -676,7 +679,7 @@ static struct tnode *inflate(struct trie
>  		    inode->pos == oldtnode->pos + oldtnode->bits &&
>  		    inode->bits > 1) {
>  			struct tnode *left, *right;
> -			t_key m = TKEY_GET_MASK(inode->pos, 1);
> +			t_key m = ~0U << (KEYLENGTH - 1) >> inode->pos;

hm, so we "know" that t_key is an unsigned int.  It makes the typedef a bit
pointless.

<wonders what an inode is doing in there>

<oh>