}
-static int is_blank_line(xrecord_t **recs, long ix, long flags)
+static int is_blank_line(xrecord_t *rec, long flags)
{
- return xdl_blankline(recs[ix]->ptr, recs[ix]->size, flags);
+ return xdl_blankline(rec->ptr, rec->size, flags);
}
-static int recs_match(xrecord_t **recs, long ixs, long ix, long flags)
+static int recs_match(xrecord_t *rec1, xrecord_t *rec2, long flags)
{
- return (recs[ixs]->ha == recs[ix]->ha &&
- xdl_recmatch(recs[ixs]->ptr, recs[ixs]->size,
- recs[ix]->ptr, recs[ix]->size,
+ return (rec1->ha == rec2->ha &&
+ xdl_recmatch(rec1->ptr, rec1->size,
+ rec2->ptr, rec2->size,
flags));
}
-int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo, long flags) {
- long ix, ixo, ixs, ixref, grpsiz, nrec = xdf->nrec;
- char *rchg = xdf->rchg, *rchgo = xdfo->rchg;
- unsigned int blank_lines;
- xrecord_t **recs = xdf->recs;
+/*
+ * If a line is indented more than this, get_indent() just returns this value.
+ * This avoids having to do absurd amounts of work for data that are not
+ * human-readable text, and also ensures that the output of get_indent fits within
+ * an int.
+ */
+#define MAX_INDENT 200
+/*
+ * Return the amount of indentation of the specified line, treating TAB as 8
+ * columns. Return -1 if line is empty or contains only whitespace. Clamp the
+ * output value at MAX_INDENT.
+ */
+static int get_indent(xrecord_t *rec)
+{
+ long i;
+ int ret = 0;
+
+ for (i = 0; i < rec->size; i++) {
+ char c = rec->ptr[i];
+
+ if (!XDL_ISSPACE(c))
+ return ret;
+ else if (c == ' ')
+ ret += 1;
+ else if (c == '\t')
+ ret += 8 - ret % 8;
+ /* ignore other whitespace characters */
+
+ if (ret >= MAX_INDENT)
+ return MAX_INDENT;
+ }
+
+ /* The line contains only whitespace. */
+ return -1;
+}
+
+/*
+ * If more than this number of consecutive blank rows are found, just return this
+ * value. This avoids requiring O(N^2) work for pathological cases, and also
+ * ensures that the output of score_split fits in an int.
+ */
+#define MAX_BLANKS 20
+
+/* Characteristics measured about a hypothetical split position. */
+struct split_measurement {
/*
- * This is the same of what GNU diff does. Move back and forward
- * change groups for a consistent and pretty diff output. This also
- * helps in finding joinable change groups and reduce the diff size.
+ * Is the split at the end of the file (aside from any blank lines)?
*/
- for (ix = ixo = 0;;) {
- /*
- * Find the first changed line in the to-be-compacted file.
- * We need to keep track of both indexes, so if we find a
- * changed lines group on the other file, while scanning the
- * to-be-compacted file, we need to skip it properly. Note
- * that loops that are testing for changed lines on rchg* do
- * not need index bounding since the array is prepared with
- * a zero at position -1 and N.
- */
- for (; ix < nrec && !rchg[ix]; ix++)
- while (rchgo[ixo++]);
- if (ix == nrec)
+ int end_of_file;
+
+ /*
+ * How much is the line immediately following the split indented (or -1 if
+ * the line is blank):
+ */
+ int indent;
+
+ /*
+ * How many consecutive lines above the split are blank?
+ */
+ int pre_blank;
+
+ /*
+ * How much is the nearest non-blank line above the split indented (or -1
+ * if there is no such line)?
+ */
+ int pre_indent;
+
+ /*
+ * How many lines after the line following the split are blank?
+ */
+ int post_blank;
+
+ /*
+ * How much is the nearest non-blank line after the line following the
+ * split indented (or -1 if there is no such line)?
+ */
+ int post_indent;
+};
+
+struct split_score {
+ /* The effective indent of this split (smaller is preferred). */
+ int effective_indent;
+
+ /* Penalty for this split (smaller is preferred). */
+ int penalty;
+};
+
+/*
+ * Fill m with information about a hypothetical split of xdf above line split.
+ */
+static void measure_split(const xdfile_t *xdf, long split,
+ struct split_measurement *m)
+{
+ long i;
+
+ if (split >= xdf->nrec) {
+ m->end_of_file = 1;
+ m->indent = -1;
+ } else {
+ m->end_of_file = 0;
+ m->indent = get_indent(xdf->recs[split]);
+ }
+
+ m->pre_blank = 0;
+ m->pre_indent = -1;
+ for (i = split - 1; i >= 0; i--) {
+ m->pre_indent = get_indent(xdf->recs[i]);
+ if (m->pre_indent != -1)
+ break;
+ m->pre_blank += 1;
+ if (m->pre_blank == MAX_BLANKS) {
+ m->pre_indent = 0;
+ break;
+ }
+ }
+
+ m->post_blank = 0;
+ m->post_indent = -1;
+ for (i = split + 1; i < xdf->nrec; i++) {
+ m->post_indent = get_indent(xdf->recs[i]);
+ if (m->post_indent != -1)
break;
+ m->post_blank += 1;
+ if (m->post_blank == MAX_BLANKS) {
+ m->post_indent = 0;
+ break;
+ }
+ }
+}
+
+/*
+ * The empirically-determined weight factors used by score_split() below.
+ * Larger values means that the position is a less favorable place to split.
+ *
+ * Note that scores are only ever compared against each other, so multiplying
+ * all of these weight/penalty values by the same factor wouldn't change the
+ * heuristic's behavior. Still, we need to set that arbitrary scale *somehow*.
+ * In practice, these numbers are chosen to be large enough that they can be
+ * adjusted relative to each other with sufficient precision despite using
+ * integer math.
+ */
+
+/* Penalty if there are no non-blank lines before the split */
+#define START_OF_FILE_PENALTY 1
+
+/* Penalty if there are no non-blank lines after the split */
+#define END_OF_FILE_PENALTY 21
+/* Multiplier for the number of blank lines around the split */
+#define TOTAL_BLANK_WEIGHT (-30)
+
+/* Multiplier for the number of blank lines after the split */
+#define POST_BLANK_WEIGHT 6
+
+/*
+ * Penalties applied if the line is indented more than its predecessor
+ */
+#define RELATIVE_INDENT_PENALTY (-4)
+#define RELATIVE_INDENT_WITH_BLANK_PENALTY 10
+
+/*
+ * Penalties applied if the line is indented less than both its predecessor and
+ * its successor
+ */
+#define RELATIVE_OUTDENT_PENALTY 24
+#define RELATIVE_OUTDENT_WITH_BLANK_PENALTY 17
+
+/*
+ * Penalties applied if the line is indented less than its predecessor but not
+ * less than its successor
+ */
+#define RELATIVE_DEDENT_PENALTY 23
+#define RELATIVE_DEDENT_WITH_BLANK_PENALTY 17
+
+/*
+ * We only consider whether the sum of the effective indents for splits are
+ * less than (-1), equal to (0), or greater than (+1) each other. The resulting
+ * value is multiplied by the following weight and combined with the penalty to
+ * determine the better of two scores.
+ */
+#define INDENT_WEIGHT 60
+
+/*
+ * Compute a badness score for the hypothetical split whose measurements are
+ * stored in m. The weight factors were determined empirically using the tools and
+ * corpus described in
+ *
+ * https://github.com/mhagger/diff-slider-tools
+ *
+ * Also see that project if you want to improve the weights based on, for example,
+ * a larger or more diverse corpus.
+ */
+static void score_add_split(const struct split_measurement *m, struct split_score *s)
+{
+ /*
+ * A place to accumulate penalty factors (positive makes this index more
+ * favored):
+ */
+ int post_blank, total_blank, indent, any_blanks;
+
+ if (m->pre_indent == -1 && m->pre_blank == 0)
+ s->penalty += START_OF_FILE_PENALTY;
+
+ if (m->end_of_file)
+ s->penalty += END_OF_FILE_PENALTY;
+
+ /*
+ * Set post_blank to the number of blank lines following the split,
+ * including the line immediately after the split:
+ */
+ post_blank = (m->indent == -1) ? 1 + m->post_blank : 0;
+ total_blank = m->pre_blank + post_blank;
+
+ /* Penalties based on nearby blank lines: */
+ s->penalty += TOTAL_BLANK_WEIGHT * total_blank;
+ s->penalty += POST_BLANK_WEIGHT * post_blank;
+
+ if (m->indent != -1)
+ indent = m->indent;
+ else
+ indent = m->post_indent;
+
+ any_blanks = (total_blank != 0);
+
+ /* Note that the effective indent is -1 at the end of the file: */
+ s->effective_indent += indent;
+
+ if (indent == -1) {
+ /* No additional adjustments needed. */
+ } else if (m->pre_indent == -1) {
+ /* No additional adjustments needed. */
+ } else if (indent > m->pre_indent) {
+ /*
+ * The line is indented more than its predecessor.
+ */
+ s->penalty += any_blanks ?
+ RELATIVE_INDENT_WITH_BLANK_PENALTY :
+ RELATIVE_INDENT_PENALTY;
+ } else if (indent == m->pre_indent) {
+ /*
+ * The line has the same indentation level as its predecessor.
+ * No additional adjustments needed.
+ */
+ } else {
/*
- * Record the start of a changed-group in the to-be-compacted file
- * and find the end of it, on both to-be-compacted and other file
- * indexes (ix and ixo).
+ * The line is indented less than its predecessor. It could be
+ * the block terminator of the previous block, but it could
+ * also be the start of a new block (e.g., an "else" block, or
+ * maybe the previous block didn't have a block terminator).
+ * Try to distinguish those cases based on what comes next:
*/
- ixs = ix;
- for (ix++; rchg[ix]; ix++);
- for (; rchgo[ixo]; ixo++);
+ if (m->post_indent != -1 && m->post_indent > indent) {
+ /*
+ * The following line is indented more. So it is likely
+ * that this line is the start of a block.
+ */
+ s->penalty += any_blanks ?
+ RELATIVE_OUTDENT_WITH_BLANK_PENALTY :
+ RELATIVE_OUTDENT_PENALTY;
+ } else {
+ /*
+ * That was probably the end of a block.
+ */
+ s->penalty += any_blanks ?
+ RELATIVE_DEDENT_WITH_BLANK_PENALTY :
+ RELATIVE_DEDENT_PENALTY;
+ }
+ }
+}
+
+static int score_cmp(struct split_score *s1, struct split_score *s2)
+{
+ /* -1 if s1.effective_indent < s2->effective_indent, etc. */
+ int cmp_indents = ((s1->effective_indent > s2->effective_indent) -
+ (s1->effective_indent < s2->effective_indent));
+
+ return INDENT_WEIGHT * cmp_indents + (s1->penalty - s2->penalty);
+}
+
+/*
+ * Represent a group of changed lines in an xdfile_t (i.e., a contiguous group
+ * of lines that was inserted or deleted from the corresponding version of the
+ * file). We consider there to be such a group at the beginning of the file, at
+ * the end of the file, and between any two unchanged lines, though most such
+ * groups will usually be empty.
+ *
+ * If the first line in a group is equal to the line following the group, then
+ * the group can be slid down. Similarly, if the last line in a group is equal
+ * to the line preceding the group, then the group can be slid up. See
+ * group_slide_down() and group_slide_up().
+ *
+ * Note that loops that are testing for changed lines in xdf->rchg do not need
+ * index bounding since the array is prepared with a zero at position -1 and N.
+ */
+struct xdlgroup {
+ /*
+ * The index of the first changed line in the group, or the index of
+ * the unchanged line above which the (empty) group is located.
+ */
+ long start;
+
+ /*
+ * The index of the first unchanged line after the group. For an empty
+ * group, end is equal to start.
+ */
+ long end;
+};
+
+/*
+ * Initialize g to point at the first group in xdf.
+ */
+static void group_init(xdfile_t *xdf, struct xdlgroup *g)
+{
+ g->start = g->end = 0;
+ while (xdf->rchg[g->end])
+ g->end++;
+}
+
+/*
+ * Move g to describe the next (possibly empty) group in xdf and return 0. If g
+ * is already at the end of the file, do nothing and return -1.
+ */
+static inline int group_next(xdfile_t *xdf, struct xdlgroup *g)
+{
+ if (g->end == xdf->nrec)
+ return -1;
+ g->start = g->end + 1;
+ for (g->end = g->start; xdf->rchg[g->end]; g->end++)
+ ;
+
+ return 0;
+}
+
+/*
+ * Move g to describe the previous (possibly empty) group in xdf and return 0.
+ * If g is already at the beginning of the file, do nothing and return -1.
+ */
+static inline int group_previous(xdfile_t *xdf, struct xdlgroup *g)
+{
+ if (g->start == 0)
+ return -1;
+
+ g->end = g->start - 1;
+ for (g->start = g->end; xdf->rchg[g->start - 1]; g->start--)
+ ;
+
+ return 0;
+}
+
+/*
+ * If g can be slid toward the end of the file, do so, and if it bumps into a
+ * following group, expand this group to include it. Return 0 on success or -1
+ * if g cannot be slid down.
+ */
+static int group_slide_down(xdfile_t *xdf, struct xdlgroup *g, long flags)
+{
+ if (g->end < xdf->nrec &&
+ recs_match(xdf->recs[g->start], xdf->recs[g->end], flags)) {
+ xdf->rchg[g->start++] = 0;
+ xdf->rchg[g->end++] = 1;
+
+ while (xdf->rchg[g->end])
+ g->end++;
+
+ return 0;
+ } else {
+ return -1;
+ }
+}
+
+/*
+ * If g can be slid toward the beginning of the file, do so, and if it bumps
+ * into a previous group, expand this group to include it. Return 0 on success
+ * or -1 if g cannot be slid up.
+ */
+static int group_slide_up(xdfile_t *xdf, struct xdlgroup *g, long flags)
+{
+ if (g->start > 0 &&
+ recs_match(xdf->recs[g->start - 1], xdf->recs[g->end - 1], flags)) {
+ xdf->rchg[--g->start] = 1;
+ xdf->rchg[--g->end] = 0;
+
+ while (xdf->rchg[g->start - 1])
+ g->start--;
+
+ return 0;
+ } else {
+ return -1;
+ }
+}
+
+static void xdl_bug(const char *msg)
+{
+ fprintf(stderr, "BUG: %s\n", msg);
+ exit(1);
+}
+
+/*
+ * Move back and forward change groups for a consistent and pretty diff output.
+ * This also helps in finding joinable change groups and reducing the diff
+ * size.
+ */
+int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo, long flags) {
+ struct xdlgroup g, go;
+ long earliest_end, end_matching_other;
+ long groupsize;
+ unsigned int blank_lines;
+
+ group_init(xdf, &g);
+ group_init(xdfo, &go);
+
+ while (1) {
+ /* If the group is empty in the to-be-compacted file, skip it: */
+ if (g.end == g.start)
+ goto next;
+
+ /*
+ * Now shift the change up and then down as far as possible in
+ * each direction. If it bumps into any other changes, merge them.
+ */
do {
- grpsiz = ix - ixs;
- blank_lines = 0;
+ groupsize = g.end - g.start;
/*
- * If the line before the current change group, is equal to
- * the last line of the current change group, shift backward
- * the group.
+ * Keep track of the last "end" index that causes this
+ * group to align with a group of changed lines in the
+ * other file. -1 indicates that we haven't found such
+ * a match yet:
*/
- while (ixs > 0 && recs_match(recs, ixs - 1, ix - 1, flags)) {
- rchg[--ixs] = 1;
- rchg[--ix] = 0;
-
- /*
- * This change might have joined two change groups,
- * so we try to take this scenario in account by moving
- * the start index accordingly (and so the other-file
- * end-of-group index).
- */
- for (; rchg[ixs - 1]; ixs--);
- while (rchgo[--ixo]);
- }
+ end_matching_other = -1;
/*
- * Record the end-of-group position in case we are matched
- * with a group of changes in the other file (that is, the
- * change record before the end-of-group index in the other
- * file is set).
+ * Boolean value that records whether there are any blank
+ * lines that could be made to be the last line of this
+ * group.
*/
- ixref = rchgo[ixo - 1] ? ix: nrec;
+ blank_lines = 0;
+
+ /* Shift the group backward as much as possible: */
+ while (!group_slide_up(xdf, &g, flags))
+ if (group_previous(xdfo, &go))
+ xdl_bug("group sync broken sliding up");
/*
- * If the first line of the current change group, is equal to
- * the line next of the current change group, shift forward
- * the group.
+ * This is this highest that this group can be shifted.
+ * Record its end index:
*/
- while (ix < nrec && recs_match(recs, ixs, ix, flags)) {
- blank_lines += is_blank_line(recs, ix, flags);
-
- rchg[ixs++] = 0;
- rchg[ix++] = 1;
-
- /*
- * This change might have joined two change groups,
- * so we try to take this scenario in account by moving
- * the start index accordingly (and so the other-file
- * end-of-group index). Keep tracking the reference
- * index in case we are shifting together with a
- * corresponding group of changes in the other file.
- */
- for (; rchg[ix]; ix++);
- while (rchgo[++ixo])
- ixref = ix;
- }
- } while (grpsiz != ix - ixs);
+ earliest_end = g.end;
- /*
- * Try to move back the possibly merged group of changes, to match
- * the recorded position in the other file.
- */
- while (ixref < ix) {
- rchg[--ixs] = 1;
- rchg[--ix] = 0;
- while (rchgo[--ixo]);
- }
+ if (go.end > go.start)
+ end_matching_other = g.end;
+
+ /* Now shift the group forward as far as possible: */
+ while (1) {
+ if (!blank_lines)
+ blank_lines = is_blank_line(
+ xdf->recs[g.end - 1],
+ flags);
+
+ if (group_slide_down(xdf, &g, flags))
+ break;
+ if (group_next(xdfo, &go))
+ xdl_bug("group sync broken sliding down");
+
+ if (go.end > go.start)
+ end_matching_other = g.end;
+ }
+ } while (groupsize != g.end - g.start);
/*
- * If a group can be moved back and forth, see if there is a
- * blank line in the moving space. If there is a blank line,
- * make sure the last blank line is the end of the group.
+ * If the group can be shifted, then we can possibly use this
+ * freedom to produce a more intuitive diff.
*
- * As we already shifted the group forward as far as possible
- * in the earlier loop, we need to shift it back only if at all.
+ * The group is currently shifted as far down as possible, so the
+ * heuristics below only have to handle upwards shifts.
*/
- if ((flags & XDF_COMPACTION_HEURISTIC) && blank_lines) {
- while (ixs > 0 &&
- !is_blank_line(recs, ix - 1, flags) &&
- recs_match(recs, ixs - 1, ix - 1, flags)) {
- rchg[--ixs] = 1;
- rchg[--ix] = 0;
+
+ if (g.end == earliest_end) {
+ /* no shifting was possible */
+ } else if (end_matching_other != -1) {
+ /*
+ * Move the possibly merged group of changes back to line
+ * up with the last group of changes from the other file
+ * that it can align with.
+ */
+ while (go.end == go.start) {
+ if (group_slide_up(xdf, &g, flags))
+ xdl_bug("match disappeared");
+ if (group_previous(xdfo, &go))
+ xdl_bug("group sync broken sliding to match");
+ }
+ } else if ((flags & XDF_COMPACTION_HEURISTIC) && blank_lines) {
+ /*
+ * Compaction heuristic: if it is possible to shift the
+ * group to make its bottom line a blank line, do so.
+ *
+ * As we already shifted the group forward as far as
+ * possible in the earlier loop, we only need to handle
+ * backward shifts, not forward ones.
+ */
+ while (!is_blank_line(xdf->recs[g.end - 1], flags)) {
+ if (group_slide_up(xdf, &g, flags))
+ xdl_bug("blank line disappeared");
+ if (group_previous(xdfo, &go))
+ xdl_bug("group sync broken sliding to blank line");
+ }
+ } else if (flags & XDF_INDENT_HEURISTIC) {
+ /*
+ * Indent heuristic: a group of pure add/delete lines
+ * implies two splits, one between the end of the "before"
+ * context and the start of the group, and another between
+ * the end of the group and the beginning of the "after"
+ * context. Some splits are aesthetically better and some
+ * are worse. We compute a badness "score" for each split,
+ * and add the scores for the two splits to define a
+ * "score" for each position that the group can be shifted
+ * to. Then we pick the shift with the lowest score.
+ */
+ long shift, best_shift = -1;
+ struct split_score best_score;
+
+ for (shift = earliest_end; shift <= g.end; shift++) {
+ struct split_measurement m;
+ struct split_score score = {0, 0};
+
+ measure_split(xdf, shift, &m);
+ score_add_split(&m, &score);
+ measure_split(xdf, shift - groupsize, &m);
+ score_add_split(&m, &score);
+ if (best_shift == -1 ||
+ score_cmp(&score, &best_score) <= 0) {
+ best_score.effective_indent = score.effective_indent;
+ best_score.penalty = score.penalty;
+ best_shift = shift;
+ }
+ }
+
+ while (g.end > best_shift) {
+ if (group_slide_up(xdf, &g, flags))
+ xdl_bug("best shift unreached");
+ if (group_previous(xdfo, &go))
+ xdl_bug("group sync broken sliding to blank line");
}
}
+
+ next:
+ /* Move past the just-processed group: */
+ if (group_next(xdf, &g))
+ break;
+ if (group_next(xdfo, &go))
+ xdl_bug("group sync broken moving to next group");
}
+ if (!group_next(xdfo, &go))
+ xdl_bug("group sync broken at end of file");
+
return 0;
}