From: Phillip Wood Date: Wed, 28 Jan 2026 10:51:49 GMT Subject: Re: [PATCH 07/10] xdiff: replace xdfile_t.dstart with xdfenv_t.delta_start Message-ID: <79ea1b9c-47cd-4702-bcb2-05417adf9eae@gmail.com> In-Reply-To: On 20/01/2026 16:32, Phillip Wood wrote: > On 02/01/2026 18:52, Ezekiel Newren via GitGitGadget wrote: >> From: Ezekiel Newren >> >> 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. Except it's only dstart that's the same, dend is different because it convinently stores an index, not an offset from the end. Having realized that, moving them to xdfenv_t makes less sense as having to calculate the dend index from an offset from the end of the array each time is a pain and sooner or later we'll make a mistake. Thanks Phillip > That explains why we start passing xdfenv_t > around rather than xdfile_t in patch 5. > > Thanks > > Phillip > >> Signed-off-by: Ezekiel Newren >> --- >>   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; > >