Re: [PATCH v4 4/6] xdiff/xdl_cleanup_records: make limits more clear
- From
- Phillip Wood <phillip.wood123@gmail.com>
- Date
- Mar 31, 2026, 09:44 UTC
- Message-ID
- <32c34d0d-9358-43e3-9d58-5999b3ffd6c2@gmail.com>
- In-Reply-To
- <75fe3ea1250ab7dfa4e029f49f2ad353185afded.1774890003.git.gitgitgadget@gmail.com>
Hi Ezekiel
On 30/03/2026 18:00, Ezekiel Newren via GitGitGadget wrote:
Show 34 quoted lines
> From: Ezekiel Newren <ezekielnewren@gmail.com>
>
> 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 <ezekielnewren@gmail.com>
> ---
> 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
Show 26 quoted lines
> + }
> +
> /*
> * 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;
> }
>
> /*