1 files changed, 440 insertions, 64 deletions

diff --git a/tree-diff.c b/tree-diff.c
index 278acc807..e7b378c8b 100644
--- a/tree-diff.c
+++ b/tree-diff.c
@@ -6,7 +6,19 @@
 #include "diffcore.h"
 #include "tree.h"
 
+/*
+ * internal mode marker, saying a tree entry != entry of tp[imin]
+ * (see ll_diff_tree_paths for what it means there)
+ *
+ * we will update/use/emit entry for diff only with it unset.
+ */
+#define S_IFXMIN_NEQ	S_DIFFTREE_IFXMIN_NEQ
+
 
+static struct combine_diff_path *ll_diff_tree_paths(
+	struct combine_diff_path *p, const unsigned char *sha1,
+	const unsigned char **parents_sha1, int nparent,
+	struct strbuf *base, struct diff_options *opt);
 static int ll_diff_tree_sha1(const unsigned char *old, const unsigned char *new,
 			     struct strbuf *base, struct diff_options *opt);
 
@@ -42,71 +54,151 @@ static int tree_entry_pathcmp(struct tree_desc *t1, struct tree_desc *t2)
 }
 
 
-/* convert path, t1/t2 -> opt->diff_*() callbacks */
-static void emit_diff(struct diff_options *opt, struct strbuf *path,
-		      struct tree_desc *t1, struct tree_desc *t2)
+/*
+ * convert path -> opt->diff_*() callbacks
+ *
+ * emits diff to first parent only, and tells diff tree-walker that we are done
+ * with p and it can be freed.
+ */
+static int emit_diff_first_parent_only(struct diff_options *opt, struct combine_diff_path *p)
 {
-	unsigned int mode1 = t1 ? t1->entry.mode : 0;
-	unsigned int mode2 = t2 ? t2->entry.mode : 0;
-
-	if (mode1 && mode2) {
-		opt->change(opt, mode1, mode2, t1->entry.sha1, t2->entry.sha1,
-			1, 1, path->buf, 0, 0);
+	struct combine_diff_parent *p0 = &p->parent[0];
+	if (p->mode && p0->mode) {
+		opt->change(opt, p0->mode, p->mode, p0->sha1, p->sha1,
+			1, 1, p->path, 0, 0);
 	}
 	else {
 		const unsigned char *sha1;
 		unsigned int mode;
 		int addremove;
 
-		if (mode2) {
+		if (p->mode) {
 			addremove = '+';
-			sha1 = t2->entry.sha1;
-			mode = mode2;
+			sha1 = p->sha1;
+			mode = p->mode;
 		} else {
 			addremove = '-';
-			sha1 = t1->entry.sha1;
-			mode = mode1;
+			sha1 = p0->sha1;
+			mode = p0->mode;
 		}
 
-		opt->add_remove(opt, addremove, mode, sha1, 1, path->buf, 0);
+		opt->add_remove(opt, addremove, mode, sha1, 1, p->path, 0);
 	}
+
+	return 0;	/* we are done with p */
 }
 
 
-/* new path should be added to diff
+/*
+ * Make a new combine_diff_path from path/mode/sha1
+ * and append it to paths list tail.
+ *
+ * Memory for created elements could be reused:
+ *
+ *	- if last->next == NULL, the memory is allocated;
+ *
+ *	- if last->next != NULL, it is assumed that p=last->next was returned
+ *	  earlier by this function, and p->next was *not* modified.
+ *	  The memory is then reused from p.
+ *
+ * so for clients,
+ *
+ * - if you do need to keep the element
+ *
+ *	p = path_appendnew(p, ...);
+ *	process(p);
+ *	p->next = NULL;
+ *
+ * - if you don't need to keep the element after processing
+ *
+ *	pprev = p;
+ *	p = path_appendnew(p, ...);
+ *	process(p);
+ *	p = pprev;
+ *	; don't forget to free tail->next in the end
+ *
+ * p->parent[] remains uninitialized.
+ */
+static struct combine_diff_path *path_appendnew(struct combine_diff_path *last,
+	int nparent, const struct strbuf *base, const char *path, int pathlen,
+	unsigned mode, const unsigned char *sha1)
+{
+	struct combine_diff_path *p;
+	int len = base->len + pathlen;
+	int alloclen = combine_diff_path_size(nparent, len);
+
+	/* if last->next is !NULL - it is a pre-allocated memory, we can reuse */
+	p = last->next;
+	if (p && (alloclen > (intptr_t)p->next)) {
+		free(p);
+		p = NULL;
+	}
+
+	if (!p) {
+		p = xmalloc(alloclen);
+
+		/*
+		 * until we go to it next round, .next holds how many bytes we
+		 * allocated (for faster realloc - we don't need copying old data).
+		 */
+		p->next = (struct combine_diff_path *)(intptr_t)alloclen;
+	}
+
+	last->next = p;
+
+	p->path = (char *)&(p->parent[nparent]);
+	memcpy(p->path, base->buf, base->len);
+	memcpy(p->path + base->len, path, pathlen);
+	p->path[len] = 0;
+	p->mode = mode;
+	hashcpy(p->sha1, sha1 ? sha1 : null_sha1);
+
+	return p;
+}
+
+/*
+ * new path should be added to combine diff
  *
  * 3 cases on how/when it should be called and behaves:
  *
- *	!t1,  t2	-> path added, parent lacks it
- *	 t1, !t2	-> path removed from parent
- *	 t1,  t2	-> path modified
+ *	 t, !tp		-> path added, all parents lack it
+ *	!t,  tp		-> path removed from all parents
+ *	 t,  tp		-> path modified/added
+ *			   (M for tp[i]=tp[imin], A otherwise)
  */
-static void show_path(struct strbuf *base, struct diff_options *opt,
-		      struct tree_desc *t1, struct tree_desc *t2)
+static struct combine_diff_path *emit_path(struct combine_diff_path *p,
+	struct strbuf *base, struct diff_options *opt, int nparent,
+	struct tree_desc *t, struct tree_desc *tp,
+	int imin)
 {
 	unsigned mode;
 	const char *path;
+	const unsigned char *sha1;
 	int pathlen;
 	int old_baselen = base->len;
-	int isdir, recurse = 0, emitthis = 1;
+	int i, isdir, recurse = 0, emitthis = 1;
 
 	/* at least something has to be valid */
-	assert(t1 || t2);
+	assert(t || tp);
 
-	if (t2) {
+	if (t) {
 		/* path present in resulting tree */
-		tree_entry_extract(t2, &path, &mode);
-		pathlen = tree_entry_len(&t2->entry);
+		sha1 = tree_entry_extract(t, &path, &mode);
+		pathlen = tree_entry_len(&t->entry);
 		isdir = S_ISDIR(mode);
 	} else {
 		/*
-		 * a path was removed - take path from parent. Also take
-		 * mode from parent, to decide on recursion.
+		 * a path was removed - take path from imin parent. Also take
+		 * mode from that parent, to decide on recursion(1).
+		 *
+		 * 1) all modes for tp[i]=tp[imin] should be the same wrt
+		 *    S_ISDIR, thanks to base_name_compare().
 		 */
-		tree_entry_extract(t1, &path, &mode);
-		pathlen = tree_entry_len(&t1->entry);
+		tree_entry_extract(&tp[imin], &path, &mode);
+		pathlen = tree_entry_len(&tp[imin].entry);
 
 		isdir = S_ISDIR(mode);
+		sha1 = NULL;
 		mode = 0;
 	}
 
@@ -115,18 +207,81 @@ static void show_path(struct strbuf *base, struct diff_options *opt,
 		emitthis = DIFF_OPT_TST(opt, TREE_IN_RECURSIVE);
 	}
 
-	strbuf_add(base, path, pathlen);
+	if (emitthis) {
+		int keep;
+		struct combine_diff_path *pprev = p;
+		p = path_appendnew(p, nparent, base, path, pathlen, mode, sha1);
+
+		for (i = 0; i < nparent; ++i) {
+			/*
+			 * tp[i] is valid, if present and if tp[i]==tp[imin] -
+			 * otherwise, we should ignore it.
+			 */
+			int tpi_valid = tp && !(tp[i].entry.mode & S_IFXMIN_NEQ);
+
+			const unsigned char *sha1_i;
+			unsigned mode_i;
+
+			p->parent[i].status =
+				!t ? DIFF_STATUS_DELETED :
+					tpi_valid ?
+						DIFF_STATUS_MODIFIED :
+						DIFF_STATUS_ADDED;
+
+			if (tpi_valid) {
+				sha1_i = tp[i].entry.sha1;
+				mode_i = tp[i].entry.mode;
+			}
+			else {
+				sha1_i = NULL;
+				mode_i = 0;
+			}
+
+			p->parent[i].mode = mode_i;
+			hashcpy(p->parent[i].sha1, sha1_i ? sha1_i : null_sha1);
+		}
 
-	if (emitthis)
-		emit_diff(opt, base, t1, t2);
+		keep = 1;
+		if (opt->pathchange)
+			keep = opt->pathchange(opt, p);
+
+		/*
+		 * If a path was filtered or consumed - we don't need to add it
+		 * to the list and can reuse its memory, leaving it as
+		 * pre-allocated element on the tail.
+		 *
+		 * On the other hand, if path needs to be kept, we need to
+		 * correct its .next to NULL, as it was pre-initialized to how
+		 * much memory was allocated.
+		 *
+		 * see path_appendnew() for details.
+		 */
+		if (!keep)
+			p = pprev;
+		else
+			p->next = NULL;
+	}
 
 	if (recurse) {
+		const unsigned char **parents_sha1;
+
+		parents_sha1 = xalloca(nparent * sizeof(parents_sha1[0]));
+		for (i = 0; i < nparent; ++i) {
+			/* same rule as in emitthis */
+			int tpi_valid = tp && !(tp[i].entry.mode & S_IFXMIN_NEQ);
+
+			parents_sha1[i] = tpi_valid ? tp[i].entry.sha1
+						    : NULL;
+		}
+
+		strbuf_add(base, path, pathlen);
 		strbuf_addch(base, '/');
-		ll_diff_tree_sha1(t1 ? t1->entry.sha1 : NULL,
-				  t2 ? t2->entry.sha1 : NULL, base, opt);
+		p = ll_diff_tree_paths(p, sha1, parents_sha1, nparent, base, opt);
+		xalloca_free(parents_sha1);
 	}
 
 	strbuf_setlen(base, old_baselen);
+	return p;
 }
 
 static void skip_uninteresting(struct tree_desc *t, struct strbuf *base,
@@ -145,59 +300,260 @@ static void skip_uninteresting(struct tree_desc *t, struct strbuf *base,
 	}
 }
 
-static int ll_diff_tree_sha1(const unsigned char *old, const unsigned char *new,
-			     struct strbuf *base, struct diff_options *opt)
+
+/*
+ * generate paths for combined diff D(sha1,parents_sha1[])
+ *
+ * Resulting paths are appended to combine_diff_path linked list, and also, are
+ * emitted on the go via opt->pathchange() callback, so it is possible to
+ * process the result as batch or incrementally.
+ *
+ * The paths are generated scanning new tree and all parents trees
+ * simultaneously, similarly to what diff_tree() was doing for 2 trees.
+ * The theory behind such scan is as follows:
+ *
+ *
+ * D(T,P1...Pn) calculation scheme
+ * -------------------------------
+ *
+ * D(T,P1...Pn) = D(T,P1) ^ ... ^ D(T,Pn)	(regarding resulting paths set)
+ *
+ *	D(T,Pj)		- diff between T..Pj
+ *	D(T,P1...Pn)	- combined diff from T to parents P1,...,Pn
+ *
+ *
+ * We start from all trees, which are sorted, and compare their entries in
+ * lock-step:
+ *
+ *	 T     P1       Pn
+ *	 -     -        -
+ *	|t|   |p1|     |pn|
+ *	|-|   |--| ... |--|      imin = argmin(p1...pn)
+ *	| |   |  |     |  |
+ *	|-|   |--|     |--|
+ *	|.|   |. |     |. |
+ *	 .     .        .
+ *	 .     .        .
+ *
+ * at any time there could be 3 cases:
+ *
+ *	1)  t < p[imin];
+ *	2)  t > p[imin];
+ *	3)  t = p[imin].
+ *
+ * Schematic deduction of what every case means, and what to do, follows:
+ *
+ * 1)  t < p[imin]  ->  ∀j t ∉ Pj  ->  "+t" ∈ D(T,Pj)  ->  D += "+t";  t↓
+ *
+ * 2)  t > p[imin]
+ *
+ *     2.1) ∃j: pj > p[imin]  ->  "-p[imin]" ∉ D(T,Pj)  ->  D += ø;  ∀ pi=p[imin]  pi↓
+ *     2.2) ∀i  pi = p[imin]  ->  pi ∉ T  ->  "-pi" ∈ D(T,Pi)  ->  D += "-p[imin]";  ∀i pi↓
+ *
+ * 3)  t = p[imin]
+ *
+ *     3.1) ∃j: pj > p[imin]  ->  "+t" ∈ D(T,Pj)  ->  only pi=p[imin] remains to investigate
+ *     3.2) pi = p[imin]  ->  investigate δ(t,pi)
+ *      |
+ *      |
+ *      v
+ *
+ *     3.1+3.2) looking at δ(t,pi) ∀i: pi=p[imin] - if all != ø  ->
+ *
+ *                       ⎧δ(t,pi)  - if pi=p[imin]
+ *              ->  D += ⎨
+ *                       ⎩"+t"     - if pi>p[imin]
+ *
+ *
+ *     in any case t↓  ∀ pi=p[imin]  pi↓
+ *
+ *
+ * ~~~~~~~~
+ *
+ * NOTE
+ *
+ *	Usual diff D(A,B) is by definition the same as combined diff D(A,[B]),
+ *	so this diff paths generator can, and is used, for plain diffs
+ *	generation too.
+ *
+ *	Please keep attention to the common D(A,[B]) case when working on the
+ *	code, in order not to slow it down.
+ *
+ * NOTE
+ *	nparent must be > 0.
+ */
+
+
+/* ∀ pi=p[imin]  pi↓ */
+static inline void update_tp_entries(struct tree_desc *tp, int nparent)
 {
-	struct tree_desc t1, t2;
-	void *t1tree, *t2tree;
+	int i;
+	for (i = 0; i < nparent; ++i)
+		if (!(tp[i].entry.mode & S_IFXMIN_NEQ))
+			update_tree_entry(&tp[i]);
+}
 
-	t1tree = fill_tree_descriptor(&t1, old);
-	t2tree = fill_tree_descriptor(&t2, new);
+static struct combine_diff_path *ll_diff_tree_paths(
+	struct combine_diff_path *p, const unsigned char *sha1,
+	const unsigned char **parents_sha1, int nparent,
+	struct strbuf *base, struct diff_options *opt)
+{
+	struct tree_desc t, *tp;
+	void *ttree, **tptree;
+	int i;
+
+	tp     = xalloca(nparent * sizeof(tp[0]));
+	tptree = xalloca(nparent * sizeof(tptree[0]));
+
+	/*
+	 * load parents first, as they are probably already cached.
+	 *
+	 * ( log_tree_diff() parses commit->parent before calling here via
+	 *   diff_tree_sha1(parent, commit) )
+	 */
+	for (i = 0; i < nparent; ++i)
+		tptree[i] = fill_tree_descriptor(&tp[i], parents_sha1[i]);
+	ttree = fill_tree_descriptor(&t, sha1);
 
 	/* Enable recursion indefinitely */
 	opt->pathspec.recursive = DIFF_OPT_TST(opt, RECURSIVE);
 
 	for (;;) {
-		int cmp;
+		int imin, cmp;
 
 		if (diff_can_quit_early(opt))
 			break;
+
 		if (opt->pathspec.nr) {
-			skip_uninteresting(&t1, base, opt);
-			skip_uninteresting(&t2, base, opt);
+			skip_uninteresting(&t, base, opt);
+			for (i = 0; i < nparent; i++)
+				skip_uninteresting(&tp[i], base, opt);
+		}
+
+		/* comparing is finished when all trees are done */
+		if (!t.size) {
+			int done = 1;
+			for (i = 0; i < nparent; ++i)
+				if (tp[i].size) {
+					done = 0;
+					break;
+				}
+			if (done)
+				break;
+		}
+
+		/*
+		 * lookup imin = argmin(p1...pn),
+		 * mark entries whether they =p[imin] along the way
+		 */
+		imin = 0;
+		tp[0].entry.mode &= ~S_IFXMIN_NEQ;
+
+		for (i = 1; i < nparent; ++i) {
+			cmp = tree_entry_pathcmp(&tp[i], &tp[imin]);
+			if (cmp < 0) {
+				imin = i;
+				tp[i].entry.mode &= ~S_IFXMIN_NEQ;
+			}
+			else if (cmp == 0) {
+				tp[i].entry.mode &= ~S_IFXMIN_NEQ;
+			}
+			else {
+				tp[i].entry.mode |= S_IFXMIN_NEQ;
+			}
 		}
-		if (!t1.size && !t2.size)
-			break;
 
-		cmp = tree_entry_pathcmp(&t1, &t2);
+		/* fixup markings for entries before imin */
+		for (i = 0; i < imin; ++i)
+			tp[i].entry.mode |= S_IFXMIN_NEQ;	/* pi > p[imin] */
 
-		/* t1 = t2 */
-		if (cmp == 0) {
-			if (DIFF_OPT_TST(opt, FIND_COPIES_HARDER) ||
-			    hashcmp(t1.entry.sha1, t2.entry.sha1) ||
-			    (t1.entry.mode != t2.entry.mode))
-				show_path(base, opt, &t1, &t2);
 
-			update_tree_entry(&t1);
-			update_tree_entry(&t2);
+
+		/* compare t vs p[imin] */
+		cmp = tree_entry_pathcmp(&t, &tp[imin]);
+
+		/* t = p[imin] */
+		if (cmp == 0) {
+			/* are either pi > p[imin] or diff(t,pi) != ø ? */
+			if (!DIFF_OPT_TST(opt, FIND_COPIES_HARDER)) {
+				for (i = 0; i < nparent; ++i) {
+					/* p[i] > p[imin] */
+					if (tp[i].entry.mode & S_IFXMIN_NEQ)
+						continue;
+
+					/* diff(t,pi) != ø */
+					if (hashcmp(t.entry.sha1, tp[i].entry.sha1) ||
+					    (t.entry.mode != tp[i].entry.mode))
+						continue;
+
+					goto skip_emit_t_tp;
+				}
+			}
+
+			/* D += {δ(t,pi) if pi=p[imin];  "+a" if pi > p[imin]} */
+			p = emit_path(p, base, opt, nparent,
+					&t, tp, imin);
+
+		skip_emit_t_tp:
+			/* t↓,  ∀ pi=p[imin]  pi↓ */
+			update_tree_entry(&t);
+			update_tp_entries(tp, nparent);
 		}
 
-		/* t1 < t2 */
+		/* t < p[imin] */
 		else if (cmp < 0) {
-			show_path(base, opt, &t1, /*t2=*/NULL);
-			update_tree_entry(&t1);
+			/* D += "+t" */
+			p = emit_path(p, base, opt, nparent,
+					&t, /*tp=*/NULL, -1);
+
+			/* t↓ */
+			update_tree_entry(&t);
 		}
 
-		/* t1 > t2 */
+		/* t > p[imin] */
 		else {
-			show_path(base, opt, /*t1=*/NULL, &t2);
-			update_tree_entry(&t2);
+			/* ∀i pi=p[imin] -> D += "-p[imin]" */
+			if (!DIFF_OPT_TST(opt, FIND_COPIES_HARDER)) {
+				for (i = 0; i < nparent; ++i)
+					if (tp[i].entry.mode & S_IFXMIN_NEQ)
+						goto skip_emit_tp;
+			}
+
+			p = emit_path(p, base, opt, nparent,
+					/*t=*/NULL, tp, imin);
+
+		skip_emit_tp:
+			/* ∀ pi=p[imin]  pi↓ */
+			update_tp_entries(tp, nparent);
 		}
 	}
 
-	free(t2tree);
-	free(t1tree);
-	return 0;
+	free(ttree);
+	for (i = nparent-1; i >= 0; i--)
+		free(tptree[i]);
+	xalloca_free(tptree);
+	xalloca_free(tp);
+
+	return p;
+}
+
+struct combine_diff_path *diff_tree_paths(
+	struct combine_diff_path *p, const unsigned char *sha1,
+	const unsigned char **parents_sha1, int nparent,
+	struct strbuf *base, struct diff_options *opt)
+{
+	p = ll_diff_tree_paths(p, sha1, parents_sha1, nparent, base, opt);
+
+	/*
+	 * free pre-allocated last element, if any
+	 * (see path_appendnew() for details about why)
+	 */
+	if (p->next) {
+		free(p->next);
+		p->next = NULL;
+	}
+
+	return p;
 }
 
 /*
@@ -308,6 +664,26 @@ static void try_to_follow_renames(const unsigned char *old, const unsigned char
 	q->nr = 1;
 }
 
+static int ll_diff_tree_sha1(const unsigned char *old, const unsigned char *new,
+			     struct strbuf *base, struct diff_options *opt)
+{
+	struct combine_diff_path phead, *p;
+	pathchange_fn_t pathchange_old = opt->pathchange;
+
+	phead.next = NULL;
+	opt->pathchange = emit_diff_first_parent_only;
+	diff_tree_paths(&phead, new, &old, 1, base, opt);
+
+	for (p = phead.next; p;) {
+		struct combine_diff_path *pprev = p;
+		p = p->next;
+		free(pprev);
+	}
+
+	opt->pathchange = pathchange_old;
+	return 0;
+}
+
 int diff_tree_sha1(const unsigned char *old, const unsigned char *new, const char *base_str, struct diff_options *opt)
 {
 	struct strbuf base;