From: Phillip Wood <phillip.wood123@gmail.com>
Date: Sun, 21 Sep 2025 13:07:02 GMT
Subject: Re: [PATCH v3 09/10] xdiff: delete rchg aliasing
Message-ID: <daad78da-752b-40f4-9c69-d6f6597ca258@gmail.com>
In-Reply-To: <fd541355609b715ebe94f9e025450165bd91d170.1758294992.git.gitgitgadget@gmail.com>

Hi Ezekiel

What is the purpose of this change. On the face of it it makes the code 
more verbose and introduces an extra pointer dereference into the loop 
condition. The compiler may lift the deference out of the loop but it 
would be helpful to know why this change is useful.

Thanks

Phillip

On 19/09/2025 16:16, Ezekiel Newren via GitGitGadget wrote:
> From: Ezekiel Newren <ezekielnewren@gmail.com>
> 
> Best-viewed-with: --color-words
> Signed-off-by: Ezekiel Newren <ezekielnewren@gmail.com>
> ---
>   xdiff/xdiffi.c | 7 +++----
>   1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/xdiff/xdiffi.c b/xdiff/xdiffi.c
> index a66125d44a..83c4cff6f7 100644
> --- a/xdiff/xdiffi.c
> +++ b/xdiff/xdiffi.c
> @@ -932,16 +932,15 @@ int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo, long flags) {
>   
>   int xdl_build_script(xdfenv_t *xe, xdchange_t **xscr) {
>   	xdchange_t *cscr = NULL, *xch;
> -	char *rchg1 = xe->xdf1.rchg, *rchg2 = xe->xdf2.rchg;
>   	long i1, i2, l1, l2;
>   
>   	/*
>   	 * Trivial. Collects "groups" of changes and creates an edit script.
>   	 */
>   	for (i1 = xe->xdf1.nrec, i2 = xe->xdf2.nrec; i1 >= 0 || i2 >= 0; i1--, i2--)
> -		if (rchg1[i1 - 1] || rchg2[i2 - 1]) {
> -			for (l1 = i1; rchg1[i1 - 1]; i1--);
> -			for (l2 = i2; rchg2[i2 - 1]; i2--);
> +		if (xe->xdf1.rchg[i1 - 1] || xe->xdf2.rchg[i2 - 1]) {
> +			for (l1 = i1; xe->xdf1.rchg[i1 - 1]; i1--);
> +			for (l2 = i2; xe->xdf2.rchg[i2 - 1]; i2--);
>   
>   			if (!(xch = xdl_add_change(cscr, i1, i2, l1 - i1, l2 - i2))) {
>   				xdl_free_script(cscr);