xdiff/xprepare: improve O(n*m) performance in xdl_cleanup_records()

In xdl_cleanup_records(), we see O(n*m) performance, where n is the
number of records from xdf->dstart to xdf->dend, and m is the size of a
bucket in xdf->rhash (<= by mlim).

Here, we improve this to O(n) by pre-computing nm (in rcrec->len(1|2))
in xdl_classify_record().

Reported-by: Marat Radchenko <marat@slonopotamus.org>
Signed-off-by: Tay Ray Chuan <rctay89@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/xdiff/xprepare.c b/xdiff/xprepare.c
index 16890852350cb62bb9f9aec5e52eea8ba46f1192..05a8f01f38a8391b74db0511e9ab0226d9448086 100644 (file)
--- a/xdiff/xprepare.c
+++ b/xdiff/xprepare.c
@@ -34,6 +34,7 @@ typedef struct s_xdlclass {
        char const *line;
        long size;
        long idx;
+       long len1, len2;
 } xdlclass_t;
 
 typedef struct s_xdlclassifier {
@@ -41,6 +42,8 @@ typedef struct s_xdlclassifier {
        long hsize;
        xdlclass_t **rchash;
        chastore_t ncha;
+       xdlclass_t **rcrecs;
+       long alloc;
        long count;
        long flags;
 } xdlclassifier_t;
@@ -50,15 +53,15 @@ typedef struct s_xdlclassifier {
 
 static int xdl_init_classifier(xdlclassifier_t *cf, long size, long flags);
 static void xdl_free_classifier(xdlclassifier_t *cf);
-static int xdl_classify_record(xdlclassifier_t *cf, xrecord_t **rhash, unsigned int hbits,
-                              xrecord_t *rec);
-static int xdl_prepare_ctx(mmfile_t *mf, long narec, xpparam_t const *xpp,
+static int xdl_classify_record(unsigned int pass, xdlclassifier_t *cf, xrecord_t **rhash,
+                              unsigned int hbits, xrecord_t *rec);
+static int xdl_prepare_ctx(unsigned int pass, mmfile_t *mf, long narec, xpparam_t const *xpp,
                           xdlclassifier_t *cf, xdfile_t *xdf);
 static void xdl_free_ctx(xdfile_t *xdf);
 static int xdl_clean_mmatch(char const *dis, long i, long s, long e);
-static int xdl_cleanup_records(xdfile_t *xdf1, xdfile_t *xdf2);
+static int xdl_cleanup_records(xdlclassifier_t *cf, xdfile_t *xdf1, xdfile_t *xdf2);
 static int xdl_trim_ends(xdfile_t *xdf1, xdfile_t *xdf2);
-static int xdl_optimize_ctxs(xdfile_t *xdf1, xdfile_t *xdf2);
+static int xdl_optimize_ctxs(xdlclassifier_t *cf, xdfile_t *xdf1, xdfile_t *xdf2);
 
 
 
@@ -83,6 +86,14 @@ static int xdl_init_classifier(xdlclassifier_t *cf, long size, long flags) {
        for (i = 0; i < cf->hsize; i++)
                cf->rchash[i] = NULL;
 
+       cf->alloc = size;
+       if (!(cf->rcrecs = (xdlclass_t **) xdl_malloc(cf->alloc * sizeof(xdlclass_t *)))) {
+
+               xdl_free(cf->rchash);
+               xdl_cha_free(&cf->ncha);
+               return -1;
+       }
+
        cf->count = 0;
 
        return 0;
@@ -91,16 +102,18 @@ static int xdl_init_classifier(xdlclassifier_t *cf, long size, long flags) {
 
 static void xdl_free_classifier(xdlclassifier_t *cf) {
 
+       xdl_free(cf->rcrecs);
        xdl_free(cf->rchash);
        xdl_cha_free(&cf->ncha);
 }
 
 
-static int xdl_classify_record(xdlclassifier_t *cf, xrecord_t **rhash, unsigned int hbits,
-                              xrecord_t *rec) {
+static int xdl_classify_record(unsigned int pass, xdlclassifier_t *cf, xrecord_t **rhash,
+                              unsigned int hbits, xrecord_t *rec) {
        long hi;
        char const *line;
        xdlclass_t *rcrec;
+       xdlclass_t **rcrecs;
 
        line = rec->ptr;
        hi = (long) XDL_HASHLONG(rec->ha, cf->hbits);
@@ -116,13 +129,25 @@ static int xdl_classify_record(xdlclassifier_t *cf, xrecord_t **rhash, unsigned
                        return -1;
                }
                rcrec->idx = cf->count++;
+               if (cf->count > cf->alloc) {
+                       cf->alloc *= 2;
+                       if (!(rcrecs = (xdlclass_t **) xdl_realloc(cf->rcrecs, cf->alloc * sizeof(xdlclass_t *)))) {
+
+                               return -1;
+                       }
+                       cf->rcrecs = rcrecs;
+               }
+               cf->rcrecs[rcrec->idx] = rcrec;
                rcrec->line = line;
                rcrec->size = rec->size;
                rcrec->ha = rec->ha;
+               rcrec->len1 = rcrec->len2 = 0;
                rcrec->next = cf->rchash[hi];
                cf->rchash[hi] = rcrec;
        }
 
+       (pass == 1) ? rcrec->len1++ : rcrec->len2++;
+
        rec->ha = (unsigned long) rcrec->idx;
 
        hi = (long) XDL_HASHLONG(rec->ha, hbits);
@@ -133,7 +158,7 @@ static int xdl_classify_record(xdlclassifier_t *cf, xrecord_t **rhash, unsigned
 }
 
 
-static int xdl_prepare_ctx(mmfile_t *mf, long narec, xpparam_t const *xpp,
+static int xdl_prepare_ctx(unsigned int pass, mmfile_t *mf, long narec, xpparam_t const *xpp,
                           xdlclassifier_t *cf, xdfile_t *xdf) {
        unsigned int hbits;
        long i, nrec, hsize, bsize;
@@ -200,7 +225,7 @@ static int xdl_prepare_ctx(mmfile_t *mf, long narec, xpparam_t const *xpp,
                        crec->ha = hav;
                        recs[nrec++] = crec;
 
-                       if (xdl_classify_record(cf, rhash, hbits, crec) < 0) {
+                       if (xdl_classify_record(pass, cf, rhash, hbits, crec) < 0) {
 
                                xdl_free(rhash);
                                xdl_free(recs);
@@ -276,28 +301,28 @@ int xdl_prepare_env(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
                return -1;
        }
 
-       if (xdl_prepare_ctx(mf1, enl1, xpp, &cf, &xe->xdf1) < 0) {
+       if (xdl_prepare_ctx(1, mf1, enl1, xpp, &cf, &xe->xdf1) < 0) {
 
                xdl_free_classifier(&cf);
                return -1;
        }
-       if (xdl_prepare_ctx(mf2, enl2, xpp, &cf, &xe->xdf2) < 0) {
+       if (xdl_prepare_ctx(2, mf2, enl2, xpp, &cf, &xe->xdf2) < 0) {
 
                xdl_free_ctx(&xe->xdf1);
                xdl_free_classifier(&cf);
                return -1;
        }
 
-       xdl_free_classifier(&cf);
-
        if (!(xpp->flags & XDF_PATIENCE_DIFF) &&
-                       xdl_optimize_ctxs(&xe->xdf1, &xe->xdf2) < 0) {
+                       xdl_optimize_ctxs(&cf, &xe->xdf1, &xe->xdf2) < 0) {
 
                xdl_free_ctx(&xe->xdf2);
                xdl_free_ctx(&xe->xdf1);
                return -1;
        }
 
+       xdl_free_classifier(&cf);
+
        return 0;
 }
 
@@ -372,11 +397,10 @@ static int xdl_clean_mmatch(char const *dis, long i, long s, long e) {
  * matches on the other file. Also, lines that have multiple matches
  * might be potentially discarded if they happear in a run of discardable.
  */
-static int xdl_cleanup_records(xdfile_t *xdf1, xdfile_t *xdf2) {
-       long i, nm, rhi, nreff, mlim;
-       unsigned long hav;
+static int xdl_cleanup_records(xdlclassifier_t *cf, xdfile_t *xdf1, xdfile_t *xdf2) {
+       long i, nm, nreff;
        xrecord_t **recs;
-       xrecord_t *rec;
+       xdlclass_t *rcrec;
        char *dis, *dis1, *dis2;
 
        if (!(dis = (char *) xdl_malloc(xdf1->nrec + xdf2->nrec + 2))) {
@@ -387,26 +411,16 @@ static int xdl_cleanup_records(xdfile_t *xdf1, xdfile_t *xdf2) {
        dis1 = dis;
        dis2 = dis1 + xdf1->nrec + 1;
 
-       if ((mlim = xdl_bogosqrt(xdf1->nrec)) > XDL_MAX_EQLIMIT)
-               mlim = XDL_MAX_EQLIMIT;
        for (i = xdf1->dstart, recs = &xdf1->recs[xdf1->dstart]; i <= xdf1->dend; i++, recs++) {
-               hav = (*recs)->ha;
-               rhi = (long) XDL_HASHLONG(hav, xdf2->hbits);
-               for (nm = 0, rec = xdf2->rhash[rhi]; rec; rec = rec->next)
-                       if (rec->ha == hav && ++nm == mlim)
-                               break;
-               dis1[i] = (nm == 0) ? 0: (nm >= mlim) ? 2: 1;
+               rcrec = cf->rcrecs[(*recs)->ha];
+               nm = rcrec ? rcrec->len2 : 0;
+               dis1[i] = (nm == 0) ? 0: 1;
        }
 
-       if ((mlim = xdl_bogosqrt(xdf2->nrec)) > XDL_MAX_EQLIMIT)
-               mlim = XDL_MAX_EQLIMIT;
        for (i = xdf2->dstart, recs = &xdf2->recs[xdf2->dstart]; i <= xdf2->dend; i++, recs++) {
-               hav = (*recs)->ha;
-               rhi = (long) XDL_HASHLONG(hav, xdf1->hbits);
-               for (nm = 0, rec = xdf1->rhash[rhi]; rec; rec = rec->next)
-                       if (rec->ha == hav && ++nm == mlim)
-                               break;
-               dis2[i] = (nm == 0) ? 0: (nm >= mlim) ? 2: 1;
+               rcrec = cf->rcrecs[(*recs)->ha];
+               nm = rcrec ? rcrec->len1 : 0;
+               dis2[i] = (nm == 0) ? 0: 1;
        }
 
        for (nreff = 0, i = xdf1->dstart, recs = &xdf1->recs[xdf1->dstart];
@@ -468,10 +482,10 @@ static int xdl_trim_ends(xdfile_t *xdf1, xdfile_t *xdf2) {
 }
 
 
-static int xdl_optimize_ctxs(xdfile_t *xdf1, xdfile_t *xdf2) {
+static int xdl_optimize_ctxs(xdlclassifier_t *cf, xdfile_t *xdf1, xdfile_t *xdf2) {
 
        if (xdl_trim_ends(xdf1, xdf2) < 0 ||
-           xdl_cleanup_records(xdf1, xdf2) < 0) {
+           xdl_cleanup_records(cf, xdf1, xdf2) < 0) {
 
                return -1;
        }