Subject: Re: [PATCH 07/10] xdiff: replace xdfile_t.dstart with xdfenv_t.delta_start

From: Phillip Wood <[email-masked]>
Date: Tue, 20 Jan 2026 16:32:54 +0000

On 02/01/2026 18:52, Ezekiel Newren via GitGitGadget wrote:
> From: Ezekiel Newren <[email-masked]>
> 
> Placing delta_start in xdfenv_t instead of xdfile_t provides a more
> appropriate context since this variable only makes sense with a pair
> of files. View with --color-words.

So as dstart and dend must be the same for both files we now store the 
values once in xdfenv_t. That explains why we start passing xdfenv_t 
around rather than xdfile_t in patch 5.

Thanks

Phillip

> Signed-off-by: Ezekiel Newren <[email-masked]>
> ---
>   xdiff/xhistogram.c |  4 ++--
>   xdiff/xpatience.c  |  4 ++--
>   xdiff/xprepare.c   | 17 +++++++++--------
>   xdiff/xtypes.h     |  3 ++-
>   4 files changed, 15 insertions(+), 13 deletions(-)
> 
> diff --git a/xdiff/xhistogram.c b/xdiff/xhistogram.c
> index 5ae1282c27..eb6a52d9ba 100644
> --- a/xdiff/xhistogram.c
> +++ b/xdiff/xhistogram.c
> @@ -365,6 +365,6 @@ out:
>   int xdl_do_histogram_diff(xpparam_t const *xpp, xdfenv_t *env)
>   {
>   	return histogram_diff(xpp, env,
> -		env->xdf1.dstart + 1, env->xdf1.dend - env->xdf1.dstart + 1,
> -		env->xdf2.dstart + 1, env->xdf2.dend - env->xdf2.dstart + 1);
> +		env->delta_start + 1, env->xdf1.dend - env->delta_start + 1,
> +		env->delta_start + 1, env->xdf2.dend - env->delta_start + 1);
>   }
> diff --git a/xdiff/xpatience.c b/xdiff/xpatience.c
> index 2bce07cf48..bd0ffbb417 100644
> --- a/xdiff/xpatience.c
> +++ b/xdiff/xpatience.c
> @@ -374,6 +374,6 @@ static int patience_diff(xpparam_t const *xpp, xdfenv_t *env,
>   int xdl_do_patience_diff(xpparam_t const *xpp, xdfenv_t *env)
>   {
>   	return patience_diff(xpp, env,
> -		env->xdf1.dstart + 1, env->xdf1.dend - env->xdf1.dstart + 1,
> -		env->xdf2.dstart + 1, env->xdf2.dend - env->xdf2.dstart + 1);
> +		env->delta_start + 1, env->xdf1.dend - env->delta_start + 1,
> +		env->delta_start + 1, env->xdf2.dend - env->delta_start + 1);
>   }
> diff --git a/xdiff/xprepare.c b/xdiff/xprepare.c
> index 06b6a6f804..e88468e74c 100644
> --- a/xdiff/xprepare.c
> +++ b/xdiff/xprepare.c
> @@ -173,7 +173,6 @@ static int xdl_prepare_ctx(mmfile_t *mf, xdfile_t *xdf, uint64_t flags) {
>   
>   	xdf->changed += 1;
>   	xdf->nreff = 0;
> -	xdf->dstart = 0;
>   	xdf->dend = xdf->nrec - 1;
>   
>   	return 0;
> @@ -287,7 +286,7 @@ static int xdl_cleanup_records(xdlclassifier_t *cf, xdfenv_t *xe) {
>   	 */
>   	if ((mlim = xdl_bogosqrt((long)xe->xdf1.nrec)) > XDL_MAX_EQLIMIT)
>   		mlim = XDL_MAX_EQLIMIT;
> -	for (i = xe->xdf1.dstart, recs = &xe->xdf1.recs[xe->xdf1.dstart]; i <= xe->xdf1.dend; i++, recs++) {
> +	for (i = xe->delta_start, recs = &xe->xdf1.recs[xe->delta_start]; i <= xe->xdf1.dend; i++, recs++) {
>   		rcrec = cf->rcrecs[recs->minimal_perfect_hash];
>   		nm = rcrec ? rcrec->len2 : 0;
>   		action1[i] = (nm == 0) ? DISCARD: (nm >= mlim && !need_min) ? INVESTIGATE: KEEP;
> @@ -295,7 +294,7 @@ static int xdl_cleanup_records(xdlclassifier_t *cf, xdfenv_t *xe) {
>   
>   	if ((mlim = xdl_bogosqrt((long)xe->xdf2.nrec)) > XDL_MAX_EQLIMIT)
>   		mlim = XDL_MAX_EQLIMIT;
> -	for (i = xe->xdf2.dstart, recs = &xe->xdf2.recs[xe->xdf2.dstart]; i <= xe->xdf2.dend; i++, recs++) {
> +	for (i = xe->delta_start, recs = &xe->xdf2.recs[xe->delta_start]; i <= xe->xdf2.dend; i++, recs++) {
>   		rcrec = cf->rcrecs[recs->minimal_perfect_hash];
>   		nm = rcrec ? rcrec->len1 : 0;
>   		action2[i] = (nm == 0) ? DISCARD: (nm >= mlim && !need_min) ? INVESTIGATE: KEEP;
> @@ -306,10 +305,10 @@ static int xdl_cleanup_records(xdlclassifier_t *cf, xdfenv_t *xe) {
>   	 * false, or become true.
>   	 */
>   	xe->xdf1.nreff = 0;
> -	for (i = xe->xdf1.dstart, recs = &xe->xdf1.recs[xe->xdf1.dstart];
> +	for (i = xe->delta_start, recs = &xe->xdf1.recs[xe->delta_start];
>   	     i <= xe->xdf1.dend; i++, recs++) {
>   		if (action1[i] == KEEP ||
> -		    (action1[i] == INVESTIGATE && !xdl_clean_mmatch(action1, i, xe->xdf1.dstart, xe->xdf1.dend))) {
> +		    (action1[i] == INVESTIGATE && !xdl_clean_mmatch(action1, i, xe->delta_start, xe->xdf1.dend))) {
>   			xe->xdf1.reference_index[xe->xdf1.nreff++] = i;
>   			/* changed[i] remains false, i.e. keep */
>   		} else
> @@ -318,10 +317,10 @@ static int xdl_cleanup_records(xdlclassifier_t *cf, xdfenv_t *xe) {
>   	}
>   
>   	xe->xdf2.nreff = 0;
> -	for (i = xe->xdf2.dstart, recs = &xe->xdf2.recs[xe->xdf2.dstart];
> +	for (i = xe->delta_start, recs = &xe->xdf2.recs[xe->delta_start];
>   	     i <= xe->xdf2.dend; i++, recs++) {
>   		if (action2[i] == KEEP ||
> -		    (action2[i] == INVESTIGATE && !xdl_clean_mmatch(action2, i, xe->xdf2.dstart, xe->xdf2.dend))) {
> +		    (action2[i] == INVESTIGATE && !xdl_clean_mmatch(action2, i, xe->delta_start, xe->xdf2.dend))) {
>   			xe->xdf2.reference_index[xe->xdf2.nreff++] = i;
>   			/* changed[i] remains false, i.e. keep */
>   		} else
> @@ -348,7 +347,7 @@ static void xdl_trim_ends(xdfenv_t *xe)
>   		size_t mph1 = xe->xdf1.recs[i].minimal_perfect_hash;
>   		size_t mph2 = xe->xdf2.recs[i].minimal_perfect_hash;
>   		if (mph1 != mph2) {
> -			xe->xdf1.dstart = xe->xdf2.dstart = (ssize_t)i;
> +			xe->delta_start = (ssize_t)i;
>   			lim -= i;
>   			break;
>   		}
> @@ -370,6 +369,8 @@ int xdl_prepare_env(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
>   		    xdfenv_t *xe) {
>   	xdlclassifier_t cf;
>   
> +	xe->delta_start = 0;
> +
>   	if (xdl_prepare_ctx(mf1, &xe->xdf1, xpp->flags) < 0) {
>   
>   		return -1;
> diff --git a/xdiff/xtypes.h b/xdiff/xtypes.h
> index 979586f20a..bda1f85eb0 100644
> --- a/xdiff/xtypes.h
> +++ b/xdiff/xtypes.h
> @@ -48,7 +48,7 @@ typedef struct s_xrecord {
>   typedef struct s_xdfile {
>   	xrecord_t *recs;
>   	size_t nrec;
> -	ptrdiff_t dstart, dend;
> +	ptrdiff_t dend;
>   	bool *changed;
>   	size_t *reference_index;
>   	size_t nreff;
> @@ -56,6 +56,7 @@ typedef struct s_xdfile {
>   
>   typedef struct s_xdfenv {
>   	xdfile_t xdf1, xdf2;
> +	size_t delta_start;
>   } xdfenv_t;
>   
>