combine-diff: cleanup.

The flag on the surviving lines meant "this parent is not
different" while the parent_map flag on the lost lines meant
"this parent is different", which was confusing.  So swap the
meaning of on-bit in the flag.  Also more heavily comment the
code.

Signed-off-by: Junio C Hamano <junkio@cox.net>

diff --git a/combine-diff.c b/combine-diff.c
index fa7af5e58c61ce1e0b6494b356e93c0d3da413e4..216a77e08805d4cefce20ca0796b49b5fc65c330 100644 (file)
--- a/combine-diff.c
+++ b/combine-diff.c
@@ -81,8 +81,8 @@ struct sline {
        struct lline *lost_head, **lost_tail;
        char *bol;
        int len;
-       /* bit 0 up to (N-1) are on if the parent does _not_
-        * have this line (i.e. we changed it).
+       /* bit 0 up to (N-1) are on if the parent has this line (i.e.
+        * we did not change it).
         * bit N is used for "interesting" lines, including context.
         */
        unsigned long flag;
@@ -219,7 +219,6 @@ static void combine_diff(const unsigned char *parent, const char *ourtmp,
        char line[MAXLINELEN];
        unsigned int lno, ob, on, nb, nn, p_lno;
        unsigned long nmask = (1UL << n);
-       unsigned long pmask = ~nmask;
        struct sline *lost_bucket = NULL;
 
        write_temp_blob(parent_tmp, parent);
@@ -265,7 +264,7 @@ static void combine_diff(const unsigned char *parent, const char *ourtmp,
                        append_lost(lost_bucket, n, line+1);
                        break;
                case '+':
-                       sline[lno-1].flag &= pmask;
+                       sline[lno-1].flag |= nmask;
                        lno++;
                        break;
                }
@@ -291,7 +290,7 @@ static void combine_diff(const unsigned char *parent, const char *ourtmp,
                                p_lno++; /* '-' means parent had it */
                        ll = ll->next;
                }
-               if (sline[lno].flag & nmask)
+               if (!(sline[lno].flag & nmask))
                        p_lno++; /* no '+' means parent had it */
        }
        sline[lno].p_lno[n] = p_lno; /* trailer */
@@ -302,7 +301,10 @@ static char combine_marker = '@';
 
 static int interesting(struct sline *sline, unsigned long all_mask)
 {
-       return ((sline->flag & all_mask) != all_mask || sline->lost_head);
+       /* If some parents lost lines here, or if we have added to
+        * some parent, it is interesting.
+        */
+       return ((sline->flag & all_mask) || sline->lost_head);
 }
 
 static unsigned long adjust_hunk_tail(struct sline *sline,
@@ -310,28 +312,35 @@ static unsigned long adjust_hunk_tail(struct sline *sline,
                                      unsigned long hunk_begin,
                                      unsigned long i)
 {
-       /* i points at the first uninteresting line.
-        * If the last line of the hunk was interesting
-        * only because it has some deletion, then
-        * it is not all that interesting for the
-        * purpose of giving trailing context lines.
+       /* i points at the first uninteresting line.  If the last line
+        * of the hunk was interesting only because it has some
+        * deletion, then it is not all that interesting for the
+        * purpose of giving trailing context lines.  This is because
+        * we output '-' line and then unmodified sline[i-1] itself in
+        * that case which gives us one extra context line.
         */
-       if ((hunk_begin + 1 <= i) &&
-           ((sline[i-1].flag & all_mask) == all_mask))
+       if ((hunk_begin + 1 <= i) && !(sline[i-1].flag & all_mask))
                i--;
        return i;
 }
 
-static unsigned long next_interesting(struct sline *sline,
-                                     unsigned long mark,
-                                     unsigned long i,
-                                     unsigned long cnt,
-                                     int uninteresting)
+static unsigned long find_next(struct sline *sline,
+                              unsigned long mark,
+                              unsigned long i,
+                              unsigned long cnt,
+                              int uninteresting)
 {
+       /* We have examined up to i-1 and are about to look at i.
+        * Find next interesting or uninteresting line.  Here,
+        * "interesting" does not mean interesting(), but marked by
+        * the give_context() function below (i.e. it includes context
+        * lines that are not interesting to interesting() function
+        * that are surrounded by interesting() ones.
+        */
        while (i < cnt)
-               if (uninteresting ?
-                   !(sline[i].flag & mark) :
-                   (sline[i].flag & mark))
+               if (uninteresting
+                   ? !(sline[i].flag & mark)
+                   : (sline[i].flag & mark))
                        return i;
                else
                        i++;
@@ -344,23 +353,37 @@ static int give_context(struct sline *sline, unsigned long cnt, int num_parent)
        unsigned long mark = (1UL<<num_parent);
        unsigned long i;
 
-       i = next_interesting(sline, mark, 0, cnt, 0);
+       /* Two groups of interesting lines may have a short gap of
+        * unintersting lines.  Connect such groups to give them a
+        * bit of context.
+        *
+        * We first start from what the interesting() function says,
+        * and mark them with "mark", and paint context lines with the
+        * mark.  So interesting() would still say false for such context
+        * lines but they are treated as "interesting" in the end.
+        */
+       i = find_next(sline, mark, 0, cnt, 0);
        if (cnt <= i)
                return 0;
 
        while (i < cnt) {
                unsigned long j = (context < i) ? (i - context) : 0;
                unsigned long k;
+
+               /* Paint a few lines before the first interesting line. */
                while (j < i)
                        sline[j++].flag |= mark;
 
        again:
-               j = next_interesting(sline, mark, i, cnt, 1);
+               /* we know up to i is to be included.  where does the
+                * next uninteresting one start?
+                */
+               j = find_next(sline, mark, i, cnt, 1);
                if (cnt <= j)
                        break; /* the rest are all interesting */
 
                /* lookahead context lines */
-               k = next_interesting(sline, mark, j, cnt, 0);
+               k = find_next(sline, mark, j, cnt, 0);
                j = adjust_hunk_tail(sline, all_mask, i, j);
 
                if (k < j + context) {
@@ -374,7 +397,8 @@ static int give_context(struct sline *sline, unsigned long cnt, int num_parent)
                }
 
                /* j is the first uninteresting line and there is
-                * no overlap beyond it within context lines.
+                * no overlap beyond it within context lines.  Paint
+                * the trailing edge a bit.
                 */
                i = k;
                k = (j + context < cnt) ? j + context : cnt;
@@ -461,7 +485,7 @@ static int make_hunks(struct sline *sline, unsigned long cnt,
                same_diff = 0;
                has_interesting = 0;
                for (j = i; j < hunk_end && !has_interesting; j++) {
-                       unsigned long this_diff = ~sline[j].flag & all_mask;
+                       unsigned long this_diff = sline[j].flag & all_mask;
                        struct lline *ll = sline[j].lost_head;
                        if (this_diff) {
                                /* This has some changes.  Is it the
@@ -532,6 +556,7 @@ static void dump_sline(struct sline *sline, unsigned long cnt, int num_parent)
                while (lno < hunk_end) {
                        struct lline *ll;
                        int j;
+                       unsigned long p_mask;
                        sl = &sline[lno++];
                        ll = sl->lost_head;
                        while (ll) {
@@ -544,11 +569,13 @@ static void dump_sline(struct sline *sline, unsigned long cnt, int num_parent)
                                puts(ll->line);
                                ll = ll->next;
                        }
+                       p_mask = 1;
                        for (j = 0; j < num_parent; j++) {
-                               if ((1UL<<j) & sl->flag)
-                                       putchar(' ');
-                               else
+                               if (p_mask & sl->flag)
                                        putchar('+');
+                               else
+                                       putchar(' ');
+                               p_mask <<= 1;
                        }
                        printf("%.*s\n", sl->len, sl->bol);
                }
@@ -574,8 +601,8 @@ static void reuse_combine_diff(struct sline *sline, unsigned long cnt,
                                ll->parent_map |= imask;
                        ll = ll->next;
                }
-               if (!(sline->flag & jmask))
-                       sline->flag &= ~imask;
+               if (sline->flag & jmask)
+                       sline->flag |= imask;
                sline++;
        }
 }
@@ -641,7 +668,7 @@ int show_combined_diff(struct combine_diff_path *elem, int num_parent,
                if (*cp == '\n') {
                        sline[lno].lost_tail = &sline[lno].lost_head;
                        sline[lno].len = cp - sline[lno].bol;
-                       sline[lno].flag = (1UL<<num_parent) - 1;
+                       sline[lno].flag = 0;
                        lno++;
                        if (lno < cnt)
                                sline[lno].bol = cp + 1;
@@ -650,7 +677,7 @@ int show_combined_diff(struct combine_diff_path *elem, int num_parent,
        if (result[size-1] != '\n') {
                sline[cnt-1].lost_tail = &sline[cnt-1].lost_head;
                sline[cnt-1].len = size - (sline[cnt-1].bol - result);
-               sline[cnt-1].flag = (1UL<<num_parent) - 1;
+               sline[cnt-1].flag = 0;
        }
 
        sline[0].p_lno = xcalloc((cnt+1) * num_parent, sizeof(unsigned long));
@@ -673,11 +700,11 @@ int show_combined_diff(struct combine_diff_path *elem, int num_parent,
 
        show_hunks = make_hunks(sline, cnt, num_parent, dense);
 
-       if (header && (show_hunks || show_empty)) {
-               shown_header++;
-               puts(header);
-       }
        if (show_hunks) {
+               if (header) {
+                       shown_header++;
+                       puts(header);
+               }
                printf("diff --%s ", dense ? "cc" : "combined");
                if (quote_c_style(elem->path, NULL, NULL, 0))
                        quote_c_style(elem->path, NULL, stdout, 0);
@@ -709,6 +736,7 @@ int show_combined_diff(struct combine_diff_path *elem, int num_parent,
                        }
                }
        }
+       free(sline[0].p_lno);
        free(sline);
        return shown_header;
 }