Subject: Re: [PATCH v4 4/6] xdiff/xdl_cleanup_records: make limits more clear

From: Phillip Wood <[email-masked]>
Date: Tue, 31 Mar 2026 10:44:15 +0100

Hi Ezekiel

On 30/03/2026 18:00, Ezekiel Newren via GitGitGadget wrote:
> From: Ezekiel Newren <[email-masked]>
> 
> Make the handling of per-file limits and the minimal-case clearer.
>    * Use explicit per-file limit variables (mlim1, mlim2) and initialize
>      them.
>    * The additional condition `!need_min` is redudant now, remove it.
> Best viewed with --color-words.
> 
> Signed-off-by: Ezekiel Newren <[email-masked]>
> ---
>   xdiff/xprepare.c | 19 ++++++++++++-------
>   1 file changed, 12 insertions(+), 7 deletions(-)
> 
> diff --git a/xdiff/xprepare.c b/xdiff/xprepare.c
> index 386668a92d..bd8baf214d 100644
> --- a/xdiff/xprepare.c
> +++ b/xdiff/xprepare.c
> @@ -268,7 +268,7 @@ static bool xdl_clean_mmatch(uint8_t const *action, ptrdiff_t i, ptrdiff_t s, pt
>    * might be potentially discarded if they appear in a run of discardable.
>    */
>   static int xdl_cleanup_records(xdlclassifier_t *cf, xdfile_t *xdf1, xdfile_t *xdf2) {
> -	ptrdiff_t i, nm, mlim;
> +	ptrdiff_t i, nm, mlim1, mlim2;
>   	xdlclass_t *rcrec;
>   	uint8_t *action1 = NULL, *action2 = NULL;
>   	bool need_min = !!(cf->flags & XDF_NEED_MINIMAL);
> @@ -287,25 +287,30 @@ static int xdl_cleanup_records(xdlclassifier_t *cf, xdfile_t *xdf1, xdfile_t *xd
>   		goto cleanup;
>   	}
>   
> +	if (need_min) {
> +		/* i.e. infinity */
> +		mlim1 = PTRDIFF_MAX;
> +		mlim2 = PTRDIFF_MAX;

This is a nice improvement as it simplifies the checks below

> +	} else {
> +		mlim1 = XDL_MIN(xdl_bogosqrt(xdf1->nrec), XDL_MAX_EQLIMIT);
> +		mlim2 = XDL_MIN(xdl_bogosqrt(xdf2->nrec), XDL_MAX_EQLIMIT);

As Junio has pointed out we now evaluate xdl_bogosqrt() twice which is 
unfortunate. It would have been nice to mention that in the commit 
message and explain why it does not matter. Personally I find the old 
code that set the limit just before each loop quite readable, the new 
version sets mlim2 a long way before it is used.

Thanks

Phillip

> +	}
> +
>   	/*
>   	 * Initialize temporary arrays with DISCARD, KEEP, or INVESTIGATE.
>   	 */
> -	if ((mlim = (long)xdl_bogosqrt((uint64_t)xdf1->nrec)) > XDL_MAX_EQLIMIT)
> -		mlim = XDL_MAX_EQLIMIT;
>   	for (i = xdf1->dstart; i <= xdf1->dend; i++) {
>   		size_t mph1 = xdf1->recs[i].minimal_perfect_hash;
>   		rcrec = cf->rcrecs[mph1];
>   		nm = rcrec ? rcrec->len2 : 0;
> -		action1[i] = (nm == 0) ? DISCARD: (nm >= mlim && !need_min) ? INVESTIGATE: KEEP;
> +		action1[i] = (nm == 0) ? DISCARD: nm >= mlim1 ? INVESTIGATE: KEEP;
>   	}
>   
> -	if ((mlim = (long)xdl_bogosqrt((uint64_t)xdf2->nrec)) > XDL_MAX_EQLIMIT)
> -		mlim = XDL_MAX_EQLIMIT;
>   	for (i = xdf2->dstart; i <= xdf2->dend; i++) {
>   		size_t mph2 = xdf2->recs[i].minimal_perfect_hash;
>   		rcrec = cf->rcrecs[mph2];
>   		nm = rcrec ? rcrec->len1 : 0;
> -		action2[i] = (nm == 0) ? DISCARD: (nm >= mlim && !need_min) ? INVESTIGATE: KEEP;
> +		action2[i] = (nm == 0) ? DISCARD: nm >= mlim2 ? INVESTIGATE: KEEP;
>   	}
>   
>   	/*