Merge pull request #6195 from libgit2/ethomson/zdiff3

merge: support zdiff3 conflict styles

22 files changed, 635 insertions, 403 deletions

diff --git a/include/git2/checkout.h b/include/git2/checkout.h
index f026d5bc2..9f834111a 100644
--- a/include/git2/checkout.h
+++ b/include/git2/checkout.h
@@ -182,7 +182,10 @@ typedef enum {
 	 * notifications; don't update the working directory or index.
 	 */
 	GIT_CHECKOUT_DRY_RUN = (1u << 24),
-	
+
+	/** Include common ancestor data in zdiff3 format for conflicts */
+	GIT_CHECKOUT_CONFLICT_STYLE_ZDIFF3 = (1u << 25),
+
 	/**
 	 * THE FOLLOWING OPTIONS ARE NOT YET IMPLEMENTED
 	 */
diff --git a/include/git2/merge.h b/include/git2/merge.h
index 3b3132f26..edd090cff 100644
--- a/include/git2/merge.h
+++ b/include/git2/merge.h
@@ -159,7 +159,10 @@ typedef enum {
 	GIT_MERGE_FILE_DIFF_PATIENCE = (1 << 6),
 
 	/** Take extra time to find minimal diff */
-	GIT_MERGE_FILE_DIFF_MINIMAL = (1 << 7)
+	GIT_MERGE_FILE_DIFF_MINIMAL = (1 << 7),
+
+	/** Create zdiff3 ("zealous diff3")-style files */
+	GIT_MERGE_FILE_STYLE_ZDIFF3 = (1 << 8)
 } git_merge_file_flag_t;
 
 #define GIT_MERGE_CONFLICT_MARKER_SIZE	7
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index e1754e5ac..e2da4bc90 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -207,7 +207,17 @@ endif()
 # errors for the xdiff sources until we've sorted them out
 if(MSVC)
 	set_source_files_properties(xdiff/xdiffi.c PROPERTIES COMPILE_FLAGS -WX-)
+	set_source_files_properties(xdiff/xemit.c PROPERTIES COMPILE_FLAGS -WX-)
+	set_source_files_properties(xdiff/xhistogram.c PROPERTIES COMPILE_FLAGS -WX-)
+	set_source_files_properties(xdiff/xmerge.c PROPERTIES COMPILE_FLAGS -WX-)
 	set_source_files_properties(xdiff/xutils.c PROPERTIES COMPILE_FLAGS -WX-)
+	set_source_files_properties(xdiff/xpatience.c PROPERTIES COMPILE_FLAGS -WX-)
+else()
+	set_source_files_properties(xdiff/xdiffi.c PROPERTIES COMPILE_FLAGS "-Wno-sign-compare -Wno-unused-parameter")
+	set_source_files_properties(xdiff/xemit.c PROPERTIES COMPILE_FLAGS "-Wno-sign-compare -Wno-unused-parameter")
+	set_source_files_properties(xdiff/xhistogram.c PROPERTIES COMPILE_FLAGS "-Wno-sign-compare")
+	set_source_files_properties(xdiff/xutils.c PROPERTIES COMPILE_FLAGS "-Wno-sign-compare")
+	set_source_files_properties(xdiff/xpatience.c PROPERTIES COMPILE_FLAGS "-Wno-sign-compare")
 endif()
 
 # Determine architecture of the machine
diff --git a/src/blame_git.c b/src/blame_git.c
index 3d514a1bc..2504b338a 100644
--- a/src/blame_git.c
+++ b/src/blame_git.c
@@ -393,7 +393,7 @@ static void fill_origin_blob(git_blame__origin *o, mmfile_t *file)
 	memset(file, 0, sizeof(*file));
 	if (o->blob) {
 		file->ptr = (char*)git_blob_rawcontent(o->blob);
-		file->size = (size_t)git_blob_rawsize(o->blob);
+		file->size = (long)git_blob_rawsize(o->blob);
 	}
 }
 
diff --git a/src/checkout.c b/src/checkout.c
index bc3048cc8..6a4643196 100644
--- a/src/checkout.c
+++ b/src/checkout.c
@@ -2070,6 +2070,9 @@ static int checkout_write_merge(
 	if (data->opts.checkout_strategy & GIT_CHECKOUT_CONFLICT_STYLE_DIFF3)
 		opts.flags |= GIT_MERGE_FILE_STYLE_DIFF3;
 
+	if (data->opts.checkout_strategy & GIT_CHECKOUT_CONFLICT_STYLE_ZDIFF3)
+		opts.flags |= GIT_MERGE_FILE_STYLE_ZDIFF3;
+
 	opts.ancestor_label = data->opts.ancestor_label ?
 		data->opts.ancestor_label : "ancestor";
 	opts.our_label = data->opts.our_label ?
@@ -2493,6 +2496,8 @@ static int checkout_data_init(
 			data->opts.checkout_strategy |= GIT_CHECKOUT_CONFLICT_STYLE_MERGE;
 		else if (strcmp(conflict_style->value, "diff3") == 0)
 			data->opts.checkout_strategy |= GIT_CHECKOUT_CONFLICT_STYLE_DIFF3;
+		else if (strcmp(conflict_style->value, "zdiff3") == 0)
+			data->opts.checkout_strategy |= GIT_CHECKOUT_CONFLICT_STYLE_ZDIFF3;
 		else {
 			git_error_set(GIT_ERROR_CHECKOUT, "unknown style '%s' given for 'merge.conflictstyle'",
 				conflict_style->value);
diff --git a/src/diff_xdiff.c b/src/diff_xdiff.c
index 278e2be36..3f6eccac1 100644
--- a/src/diff_xdiff.c
+++ b/src/diff_xdiff.c
@@ -218,14 +218,9 @@ static int git_xdiff(git_patch_generated_output *output, git_patch_generated *pa
 	 * updates are needed to xo->params.flags
 	 */
 
-	git_patch_generated_old_data(&info.xd_old_data.ptr, &info.xd_old_data.size, patch);
-	git_patch_generated_new_data(&info.xd_new_data.ptr, &info.xd_new_data.size, patch);
-
-	if (info.xd_old_data.size > GIT_XDIFF_MAX_SIZE ||
-		info.xd_new_data.size > GIT_XDIFF_MAX_SIZE) {
-		git_error_set(GIT_ERROR_INVALID, "files too large for diff");
+	if (git_patch_generated_old_data(&info.xd_old_data.ptr, &info.xd_old_data.size, patch) < 0 ||
+	    git_patch_generated_new_data(&info.xd_new_data.ptr, &info.xd_new_data.size, patch) < 0)
 		return -1;
-	}
 
 	xdl_diff(&info.xd_old_data, &info.xd_new_data,
 		&xo->params, &xo->config, &xo->callback);
@@ -261,5 +256,5 @@ void git_xdiff_init(git_xdiff_output *xo, const git_diff_options *opts)
 	if (flags & GIT_DIFF_IGNORE_BLANK_LINES)
 		xo->params.flags |= XDF_IGNORE_BLANK_LINES;
 
-	xo->callback.outf = git_xdiff_cb;
+	xo->callback.out_line = git_xdiff_cb;
 }
diff --git a/src/merge_file.c b/src/merge_file.c
index bfa3ec52e..732a047b1 100644
--- a/src/merge_file.c
+++ b/src/merge_file.c
@@ -86,22 +86,30 @@ static int merge_file__xdiff(
 
 	memset(&xmparam, 0x0, sizeof(xmparam_t));
 
+	if (ours->size > LONG_MAX ||
+	    theirs->size > LONG_MAX ||
+	    (ancestor && ancestor->size > LONG_MAX)) {
+		git_error_set(GIT_ERROR_MERGE, "failed to merge files");
+		error = -1;
+		goto done;
+	}
+
 	if (ancestor) {
 		xmparam.ancestor = (options.ancestor_label) ?
 			options.ancestor_label : ancestor->path;
 		ancestor_mmfile.ptr = (char *)ancestor->ptr;
-		ancestor_mmfile.size = ancestor->size;
+		ancestor_mmfile.size = (long)ancestor->size;
 	}
 
 	xmparam.file1 = (options.our_label) ?
 		options.our_label : ours->path;
 	our_mmfile.ptr = (char *)ours->ptr;
-	our_mmfile.size = ours->size;
+	our_mmfile.size = (long)ours->size;
 
 	xmparam.file2 = (options.their_label) ?
 		options.their_label : theirs->path;
 	their_mmfile.ptr = (char *)theirs->ptr;
-	their_mmfile.size = theirs->size;
+	their_mmfile.size = (long)theirs->size;
 
 	if (options.favor == GIT_MERGE_FILE_FAVOR_OURS)
 		xmparam.favor = XDL_MERGE_FAVOR_OURS;
@@ -115,6 +123,8 @@ static int merge_file__xdiff(
 
 	if (options.flags & GIT_MERGE_FILE_STYLE_DIFF3)
 		xmparam.style = XDL_MERGE_DIFF3;
+	if (options.flags & GIT_MERGE_FILE_STYLE_ZDIFF3)
+		xmparam.style = XDL_MERGE_ZEALOUS_DIFF3;
 
 	if (options.flags & GIT_MERGE_FILE_IGNORE_WHITESPACE)
 		xmparam.xpp.flags |= XDF_IGNORE_WHITESPACE;
diff --git a/src/patch_generate.c b/src/patch_generate.c
index 6d115affe..bc598fea8 100644
--- a/src/patch_generate.c
+++ b/src/patch_generate.c
@@ -750,18 +750,34 @@ git_diff_driver *git_patch_generated_driver(git_patch_generated *patch)
 	return patch->ofile.driver;
 }
 
-void git_patch_generated_old_data(
-	char **ptr, size_t *len, git_patch_generated *patch)
+int git_patch_generated_old_data(
+	char **ptr, long *len, git_patch_generated *patch)
 {
+	if (patch->ofile.map.len > LONG_MAX ||
+	    patch->ofile.map.len > GIT_XDIFF_MAX_SIZE) {
+		git_error_set(GIT_ERROR_INVALID, "files too large for diff");
+		return -1;
+	}
+
 	*ptr = patch->ofile.map.data;
-	*len = patch->ofile.map.len;
+	*len = (long)patch->ofile.map.len;
+
+	return 0;
 }
 
-void git_patch_generated_new_data(
-	char **ptr, size_t *len, git_patch_generated *patch)
+int git_patch_generated_new_data(
+	char **ptr, long *len, git_patch_generated *patch)
 {
+	if (patch->ofile.map.len > LONG_MAX ||
+	    patch->ofile.map.len > GIT_XDIFF_MAX_SIZE) {
+		git_error_set(GIT_ERROR_INVALID, "files too large for diff");
+		return -1;
+	}
+
 	*ptr = patch->nfile.map.data;
-	*len = patch->nfile.map.len;
+	*len = (long)patch->nfile.map.len;
+
+	return 0;
 }
 
 static int patch_generated_file_cb(
diff --git a/src/patch_generate.h b/src/patch_generate.h
index 0e09d27ca..56e3e9df4 100644
--- a/src/patch_generate.h
+++ b/src/patch_generate.h
@@ -39,10 +39,10 @@ typedef struct git_patch_generated git_patch_generated;
 
 extern git_diff_driver *git_patch_generated_driver(git_patch_generated *);
 
-extern void git_patch_generated_old_data(
-	char **, size_t *, git_patch_generated *);
-extern void git_patch_generated_new_data(
-	char **, size_t *, git_patch_generated *);
+extern int git_patch_generated_old_data(
+	char **, long *, git_patch_generated *);
+extern int git_patch_generated_new_data(
+	char **, long *, git_patch_generated *);
 extern int git_patch_generated_from_diff(
 	git_patch **, git_diff *, size_t);
 
diff --git a/src/xdiff/git-xdiff.h b/src/xdiff/git-xdiff.h
new file mode 100644
index 000000000..0b4f0bc04
--- /dev/null
+++ b/src/xdiff/git-xdiff.h
@@ -0,0 +1,42 @@
+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+
+/*
+ * This file provides the necessary indirection between xdiff and
+ * libgit2.  libgit2-specific functionality should live here, so
+ * that git and libgit2 can share a common xdiff implementation.
+ */
+
+#ifndef INCLUDE_git_xdiff_h__
+#define INCLUDE_git_xdiff_h__
+
+#include "regexp.h"
+
+#define xdl_malloc(x) git__malloc(x)
+#define xdl_free(ptr) git__free(ptr)
+#define xdl_realloc(ptr, x) git__realloc(ptr, x)
+
+#define XDL_BUG(msg) GIT_ASSERT(msg)
+
+#define xdl_regex_t git_regexp
+#define xdl_regmatch_t git_regmatch
+
+GIT_INLINE(int) xdl_regexec_buf(
+	const xdl_regex_t *preg, const char *buf, size_t size,
+	size_t nmatch, xdl_regmatch_t pmatch[], int eflags)
+{
+	GIT_UNUSED(preg);
+	GIT_UNUSED(buf);
+	GIT_UNUSED(size);
+	GIT_UNUSED(nmatch);
+	GIT_UNUSED(pmatch);
+	GIT_UNUSED(eflags);
+	GIT_ASSERT("not implemented");
+	return -1;
+}
+
+#endif
diff --git a/src/xdiff/xdiff.h b/src/xdiff/xdiff.h
index 5b13e77a0..a7bf17cd6 100644
--- a/src/xdiff/xdiff.h
+++ b/src/xdiff/xdiff.h
@@ -23,6 +23,8 @@
 #if !defined(XDIFF_H)
 #define XDIFF_H
 
+#include "git-xdiff.h"
+
 #ifdef __cplusplus
 extern "C" {
 #endif /* #ifdef __cplusplus */
@@ -50,16 +52,9 @@ extern "C" {
 
 /* xdemitconf_t.flags */
 #define XDL_EMIT_FUNCNAMES (1 << 0)
+#define XDL_EMIT_NO_HUNK_HDR (1 << 1)
 #define XDL_EMIT_FUNCCONTEXT (1 << 2)
 
-#define XDL_MMB_READONLY (1 << 0)
-
-#define XDL_MMF_ATOMIC (1 << 0)
-
-#define XDL_BDOP_INS 1
-#define XDL_BDOP_CPY 2
-#define XDL_BDOP_INSB 3
-
 /* merge simplification levels */
 #define XDL_MERGE_MINIMAL 0
 #define XDL_MERGE_EAGER 1
@@ -73,20 +68,25 @@ extern "C" {
 
 /* merge output styles */
 #define XDL_MERGE_DIFF3 1
+#define XDL_MERGE_ZEALOUS_DIFF3 2
 
 typedef struct s_mmfile {
 	char *ptr;
-	size_t size;
+	long size;
 } mmfile_t;
 
 typedef struct s_mmbuffer {
 	char *ptr;
-	size_t size;
+	long size;
 } mmbuffer_t;
 
 typedef struct s_xpparam {
 	unsigned long flags;
 
+	/* -I<regex> */
+	xdl_regex_t **ignore_regex;
+	size_t ignore_regex_nr;
+
 	/* See Documentation/diff-options.txt. */
 	char **anchors;
 	size_t anchors_nr;
@@ -94,7 +94,11 @@ typedef struct s_xpparam {
 
 typedef struct s_xdemitcb {
 	void *priv;
-	int (*outf)(void *, mmbuffer_t *, int);
+	int (*out_hunk)(void *,
+			long old_begin, long old_nr,
+			long new_begin, long new_nr,
+			const char *func, long funclen);
+	int (*out_line)(void *, mmbuffer_t *, int);
 } xdemitcb_t;
 
 typedef long (*find_func_t)(const char *line, long line_len, char *buffer, long buffer_size, void *priv);
@@ -117,10 +121,6 @@ typedef struct s_bdiffparam {
 } bdiffparam_t;
 
 
-#define xdl_malloc(x) git__malloc(x)
-#define xdl_free(ptr) git__free(ptr)
-#define xdl_realloc(ptr,x) git__realloc(ptr,x)
-
 void *xdl_mmfile_first(mmfile_t *mmf, long *size);
 long xdl_mmfile_size(mmfile_t *mmf);
 
diff --git a/src/xdiff/xdiffi.c b/src/xdiff/xdiffi.c
index 916295b44..af31b7f4b 100644
--- a/src/xdiff/xdiffi.c
+++ b/src/xdiff/xdiffi.c
@@ -21,8 +21,6 @@
  */
 
 #include "xinclude.h"
-#include "integer.h"
-
 
 #define XDL_MAX_COST_MIN 256
 #define XDL_HEUR_MIN_COST 256
@@ -30,41 +28,19 @@
 #define XDL_SNAKE_CNT 20
 #define XDL_K_HEUR 4
 
-/** Declare a function as always inlined. */
-#if defined(_MSC_VER)
-# define XDL_INLINE(type) static __inline type
-#elif defined(__GNUC__)
-# define XDL_INLINE(type) static __inline__ type
-#else
-# define XDL_INLINE(type) static type
-#endif
-
 typedef struct s_xdpsplit {
 	long i1, i2;
 	int min_lo, min_hi;
 } xdpsplit_t;
 
-
-
-
-static long xdl_split(unsigned long const *ha1, long off1, long lim1,
-		      unsigned long const *ha2, long off2, long lim2,
-		      long *kvdf, long *kvdb, int need_min, xdpsplit_t *spl,
-		      xdalgoenv_t *xenv);
-static xdchange_t *xdl_add_change(xdchange_t *xscr, long i1, long i2, long chg1, long chg2);
-
-
-
-
-
 /*
  * See "An O(ND) Difference Algorithm and its Variations", by Eugene Myers.
  * Basically considers a "box" (off1, off2, lim1, lim2) and scan from both
  * the forward diagonal starting from (off1, off2) and the backward diagonal
  * starting from (lim1, lim2). If the K values on the same diagonal crosses
- * returns the furthest point of reach. We might end up having to expensive
- * cases using this algorithm is full, so a little bit of heuristic is needed
- * to cut the search and to return a suboptimal point.
+ * returns the furthest point of reach. We might encounter expensive edge cases
+ * using this algorithm, so a little bit of heuristic is needed to cut the
+ * search and to return a suboptimal point.
  */
 static long xdl_split(unsigned long const *ha1, long off1, long lim1,
 		      unsigned long const *ha2, long off2, long lim2,
@@ -87,11 +63,13 @@ static long xdl_split(unsigned long const *ha1, long off1, long lim1,
 		int got_snake = 0;
 
 		/*
-		 * We need to extent the diagonal "domain" by one. If the next
+		 * We need to extend the diagonal "domain" by one. If the next
 		 * values exits the box boundaries we need to change it in the
-		 * opposite direction because (max - min) must be a power of two.
+		 * opposite direction because (max - min) must be a power of
+		 * two.
+		 *
 		 * Also we initialize the external K value to -1 so that we can
-		 * avoid extra conditions check inside the core loop.
+		 * avoid extra conditions in the check inside the core loop.
 		 */
 		if (fmin > dmin)
 			kvdf[--fmin - 1] = -1;
@@ -122,11 +100,13 @@ static long xdl_split(unsigned long const *ha1, long off1, long lim1,
 		}
 
 		/*
-		 * We need to extent the diagonal "domain" by one. If the next
+		 * We need to extend the diagonal "domain" by one. If the next
 		 * values exits the box boundaries we need to change it in the
-		 * opposite direction because (max - min) must be a power of two.
+		 * opposite direction because (max - min) must be a power of
+		 * two.
+		 *
 		 * Also we initialize the external K value to -1 so that we can
-		 * avoid extra conditions check inside the core loop.
+		 * avoid extra conditions in the check inside the core loop.
 		 */
 		if (bmin > dmin)
 			kvdb[--bmin - 1] = XDL_LINE_MAX;
@@ -162,7 +142,7 @@ static long xdl_split(unsigned long const *ha1, long off1, long lim1,
 		/*
 		 * If the edit cost is above the heuristic trigger and if
 		 * we got a good snake, we sample current diagonals to see
-		 * if some of the, have reached an "interesting" path. Our
+		 * if some of them have reached an "interesting" path. Our
 		 * measure is a function of the distance from the diagonal
 		 * corner (i1 + i2) penalized with the distance from the
 		 * mid diagonal itself. If this value is above the current
@@ -220,8 +200,9 @@ static long xdl_split(unsigned long const *ha1, long off1, long lim1,
 		}
 
 		/*
-		 * Enough is enough. We spent too much time here and now we collect
-		 * the furthest reaching path using the (i1 + i2) measure.
+		 * Enough is enough. We spent too much time here and now we
+		 * collect the furthest reaching path using the (i1 + i2)
+		 * measure.
 		 */
 		if (ec >= xenv->mxcost) {
 			long fbest, fbest1, bbest, bbest1;
@@ -268,9 +249,9 @@ static long xdl_split(unsigned long const *ha1, long off1, long lim1,
 
 
 /*
- * Rule: "Divide et Impera". Recursively split the box in sub-boxes by calling
- * the box splitting function. Note that the real job (marking changed lines)
- * is done in the two boundary reaching checks.
+ * Rule: "Divide et Impera" (divide & conquer). Recursively split the box in
+ * sub-boxes by calling the box splitting function. Note that the real job
+ * (marking changed lines) is done in the two boundary reaching checks.
  */
 int xdl_recs_cmp(diffdata_t *dd1, long off1, long lim1,
 		 diffdata_t *dd2, long off2, long lim2,
@@ -330,7 +311,7 @@ int xdl_recs_cmp(diffdata_t *dd1, long off1, long lim1,
 
 int xdl_do_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
 		xdfenv_t *xe) {
-	size_t ndiags, allocsize;
+	long ndiags;
 	long *kvd, *kvdf, *kvdb;
 	xdalgoenv_t xenv;
 	diffdata_t dd1, dd2;
@@ -347,15 +328,14 @@ int xdl_do_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
 	}
 
 	/*
-	 * Allocate and setup K vectors to be used by the differential algorithm.
+	 * Allocate and setup K vectors to be used by the differential
+	 * algorithm.
+	 *
 	 * One is to store the forward path and one to store the backward path.
 	 */
-	GIT_ERROR_CHECK_ALLOC_ADD3(&ndiags, xe->xdf1.nreff, xe->xdf2.nreff, 3);
-	GIT_ERROR_CHECK_ALLOC_MULTIPLY(&allocsize, ndiags, 2);
-	GIT_ERROR_CHECK_ALLOC_ADD(&allocsize, allocsize, 2);
-	GIT_ERROR_CHECK_ALLOC_MULTIPLY(&allocsize, allocsize, sizeof(long));
+	ndiags = xe->xdf1.nreff + xe->xdf2.nreff + 3;
+	if (!(kvd = (long *) xdl_malloc((2 * ndiags + 2) * sizeof(long)))) {
 
-	if (!(kvd = (long *) xdl_malloc(allocsize))) {
 		xdl_free_env(xe);
 		return -1;
 	}
@@ -410,19 +390,16 @@ static xdchange_t *xdl_add_change(xdchange_t *xscr, long i1, long i2, long chg1,
 }
 
 
-static int recs_match(xrecord_t *rec1, xrecord_t *rec2, long flags)
+static int recs_match(xrecord_t *rec1, xrecord_t *rec2)
 {
-	return (rec1->ha == rec2->ha &&
-		xdl_recmatch(rec1->ptr, rec1->size,
-			     rec2->ptr, rec2->size,
-			     flags));
+	return (rec1->ha == rec2->ha);
 }
 
 /*
  * 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.
+ * human-readable text, and also ensures that the output of get_indent fits
+ * within an int.
  */
 #define MAX_INDENT 200
 
@@ -456,9 +433,9 @@ static int get_indent(xrecord_t *rec)
 }
 
 /*
- * 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.
+ * 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
 
@@ -470,8 +447,8 @@ struct split_measurement {
 	int end_of_file;
 
 	/*
-	 * How much is the line immediately following the split indented (or -1 if
-	 * the line is blank):
+	 * How much is the line immediately following the split indented (or -1
+	 * if the line is blank):
 	 */
 	int indent;
 
@@ -481,8 +458,8 @@ struct split_measurement {
 	int pre_blank;
 
 	/*
-	 * How much is the nearest non-blank line above the split indented (or -1
-	 * if there is no such line)?
+	 * How much is the nearest non-blank line above the split indented (or
+	 * -1 if there is no such line)?
 	 */
 	int pre_indent;
 
@@ -602,14 +579,19 @@ static void measure_split(const xdfile_t *xdf, long split,
 #define INDENT_WEIGHT 60
 
 /*
+ * How far do we slide a hunk at most?
+ */
+#define INDENT_HEURISTIC_MAX_SLIDING 100
+
+/*
  * 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
+ * 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.
+ * 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)
 {
@@ -741,7 +723,7 @@ static void group_init(xdfile_t *xdf, struct xdlgroup *g)
  * 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.
  */
-XDL_INLINE(int) group_next(xdfile_t *xdf, struct xdlgroup *g)
+static inline int group_next(xdfile_t *xdf, struct xdlgroup *g)
 {
 	if (g->end == xdf->nrec)
 		return -1;
@@ -757,7 +739,7 @@ XDL_INLINE(int) group_next(xdfile_t *xdf, struct xdlgroup *g)
  * 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.
  */
-XDL_INLINE(int) group_previous(xdfile_t *xdf, struct xdlgroup *g)
+static inline int group_previous(xdfile_t *xdf, struct xdlgroup *g)
 {
 	if (g->start == 0)
 		return -1;
@@ -774,10 +756,10 @@ XDL_INLINE(int) group_previous(xdfile_t *xdf, struct xdlgroup *g)
  * 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)
+static int group_slide_down(xdfile_t *xdf, struct xdlgroup *g)
 {
 	if (g->end < xdf->nrec &&
-	    recs_match(xdf->recs[g->start], xdf->recs[g->end], flags)) {
+	    recs_match(xdf->recs[g->start], xdf->recs[g->end])) {
 		xdf->rchg[g->start++] = 0;
 		xdf->rchg[g->end++] = 1;
 
@@ -795,10 +777,10 @@ static int group_slide_down(xdfile_t *xdf, struct xdlgroup *g, long flags)
  * 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)
+static int group_slide_up(xdfile_t *xdf, struct xdlgroup *g)
 {
 	if (g->start > 0 &&
-	    recs_match(xdf->recs[g->start - 1], xdf->recs[g->end - 1], flags)) {
+	    recs_match(xdf->recs[g->start - 1], xdf->recs[g->end - 1])) {
 		xdf->rchg[--g->start] = 1;
 		xdf->rchg[--g->end] = 0;
 
@@ -811,12 +793,6 @@ static int group_slide_up(xdfile_t *xdf, struct xdlgroup *g, long flags)
 	}
 }
 
-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
@@ -831,13 +807,16 @@ int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo, long flags) {
 	group_init(xdfo, &go);
 
 	while (1) {
-		/* If the group is empty in the to-be-compacted file, skip it: */
+		/*
+		 * 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.
+		 * each direction. If it bumps into any other changes, merge
+		 * them.
 		 */
 		do {
 			groupsize = g.end - g.start;
@@ -851,9 +830,9 @@ int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo, long flags) {
 			end_matching_other = -1;
 
 			/* Shift the group backward as much as possible: */
-			while (!group_slide_up(xdf, &g, flags))
+			while (!group_slide_up(xdf, &g))
 				if (group_previous(xdfo, &go))
-					xdl_bug("group sync broken sliding up");
+					XDL_BUG("group sync broken sliding up");
 
 			/*
 			 * This is this highest that this group can be shifted.
@@ -866,10 +845,10 @@ int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo, long flags) {
 
 			/* Now shift the group forward as far as possible: */
 			while (1) {
-				if (group_slide_down(xdf, &g, flags))
+				if (group_slide_down(xdf, &g))
 					break;
 				if (group_next(xdfo, &go))
-					xdl_bug("group sync broken sliding down");
+					XDL_BUG("group sync broken sliding down");
 
 				if (go.end > go.start)
 					end_matching_other = g.end;
@@ -880,40 +859,46 @@ int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo, long flags) {
 		 * If the group can be shifted, then we can possibly use this
 		 * freedom to produce a more intuitive diff.
 		 *
-		 * The group is currently shifted as far down as possible, so the
-		 * heuristics below only have to handle upwards shifts.
+		 * The group is currently shifted as far down as possible, so
+		 * the heuristics below only have to handle upwards shifts.
 		 */
 
 		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.
+			 * 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_slide_up(xdf, &g))
+					XDL_BUG("match disappeared");
 				if (group_previous(xdfo, &go))
-					xdl_bug("group sync broken sliding to match");
+					XDL_BUG("group sync broken sliding to match");
 			}
 		} 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.
+			 * 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++) {
+			shift = earliest_end;
+			if (g.end - groupsize - 1 > shift)
+				shift = g.end - groupsize - 1;
+			if (g.end - INDENT_HEURISTIC_MAX_SLIDING > shift)
+				shift = g.end - INDENT_HEURISTIC_MAX_SLIDING;
+			for (; shift <= g.end; shift++) {
 				struct split_measurement m;
 				struct split_score score = {0, 0};
 
@@ -930,10 +915,10 @@ int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo, long flags) {
 			}
 
 			while (g.end > best_shift) {
-				if (group_slide_up(xdf, &g, flags))
-					xdl_bug("best shift unreached");
+				if (group_slide_up(xdf, &g))
+					XDL_BUG("best shift unreached");
 				if (group_previous(xdfo, &go))
-					xdl_bug("group sync broken sliding to blank line");
+					XDL_BUG("group sync broken sliding to blank line");
 			}
 		}
 
@@ -942,11 +927,11 @@ int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo, long flags) {
 		if (group_next(xdf, &g))
 			break;
 		if (group_next(xdfo, &go))
-			xdl_bug("group sync broken moving to next group");
+			XDL_BUG("group sync broken moving to next group");
 	}
 
 	if (!group_next(xdfo, &go))
-		xdl_bug("group sync broken at end of file");
+		XDL_BUG("group sync broken at end of file");
 
 	return 0;
 }
@@ -992,8 +977,6 @@ static int xdl_call_hunk_func(xdfenv_t *xe, xdchange_t *xscr, xdemitcb_t *ecb,
 {
 	xdchange_t *xch, *xche;
 
-	(void)xe;
-
 	for (xch = xscr; xch; xch = xche->next) {
 		xche = xdl_get_hunk(&xch, xecfg);
 		if (!xch)
@@ -1006,7 +989,7 @@ static int xdl_call_hunk_func(xdfenv_t *xe, xdchange_t *xscr, xdemitcb_t *ecb,
 	return 0;
 }
 
-static void xdl_mark_ignorable(xdchange_t *xscr, xdfenv_t *xe, long flags)
+static void xdl_mark_ignorable_lines(xdchange_t *xscr, xdfenv_t *xe, long flags)
 {
 	xdchange_t *xch;
 
@@ -1027,6 +1010,46 @@ static void xdl_mark_ignorable(xdchange_t *xscr, xdfenv_t *xe, long flags)
 	}
 }
 
+static int record_matches_regex(xrecord_t *rec, xpparam_t const *xpp) {
+	xdl_regmatch_t regmatch;
+	int i;
+
+	for (i = 0; i < xpp->ignore_regex_nr; i++)
+		if (!xdl_regexec_buf(xpp->ignore_regex[i], rec->ptr, rec->size, 1,
+				 &regmatch, 0))
+			return 1;
+
+	return 0;
+}
+
+static void xdl_mark_ignorable_regex(xdchange_t *xscr, const xdfenv_t *xe,
+				     xpparam_t const *xpp)
+{
+	xdchange_t *xch;
+
+	for (xch = xscr; xch; xch = xch->next) {
+		xrecord_t **rec;
+		int ignore = 1;
+		long i;
+
+		/*
+		 * Do not override --ignore-blank-lines.
+		 */
+		if (xch->ignore)
+			continue;
+
+		rec = &xe->xdf1.recs[xch->i1];
+		for (i = 0; i < xch->chg1 && ignore; i++)
+			ignore = record_matches_regex(rec[i], xpp);
+
+		rec = &xe->xdf2.recs[xch->i2];
+		for (i = 0; i < xch->chg2 && ignore; i++)
+			ignore = record_matches_regex(rec[i], xpp);
+
+		xch->ignore = ignore;
+	}
+}
+
 int xdl_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
 	     xdemitconf_t const *xecfg, xdemitcb_t *ecb) {
 	xdchange_t *xscr;
@@ -1046,7 +1069,10 @@ int xdl_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
 	}
 	if (xscr) {
 		if (xpp->flags & XDF_IGNORE_BLANK_LINES)
-			xdl_mark_ignorable(xscr, &xe, xpp->flags);
+			xdl_mark_ignorable_lines(xscr, &xe, xpp->flags);
+
+		if (xpp->ignore_regex)
+			xdl_mark_ignorable_regex(xscr, &xe, xpp);
 
 		if (ef(&xe, xscr, ecb, xecfg) < 0) {
 
diff --git a/src/xdiff/xemit.c b/src/xdiff/xemit.c
index 0ffa6553a..1cbf2b982 100644
--- a/src/xdiff/xemit.c
+++ b/src/xdiff/xemit.c
@@ -31,7 +31,7 @@ static long xdl_get_rec(xdfile_t *xdf, long ri, char const **rec) {
 
 
 static int xdl_emit_record(xdfile_t *xdf, long ri, char const *pre, xdemitcb_t *ecb) {
-	long size, psize = (long)strlen(pre);
+	long size, psize = strlen(pre);
 	char const *rec;
 
 	size = xdl_get_rec(xdf, ri, &rec);
@@ -81,7 +81,7 @@ xdchange_t *xdl_get_hunk(xdchange_t **xscr, xdemitconf_t const *xecfg)
 		} else if (distance < max_ignorable && xch->ignore) {
 			ignored += xch->chg2;
 		} else if (lxch != xchp &&
-			   xch->i1 + ignored - (lxch->i1 + lxch->chg1) > (unsigned long)max_common) {
+			   xch->i1 + ignored - (lxch->i1 + lxch->chg1) > max_common) {
 			break;
 		} else if (!xch->ignore) {
 			lxch = xch;
@@ -97,8 +97,6 @@ xdchange_t *xdl_get_hunk(xdchange_t **xscr, xdemitconf_t const *xecfg)
 
 static long def_ff(const char *rec, long len, char *buf, long sz, void *priv)
 {
-	(void)priv;
-
 	if (len > 0 &&
 			(isalpha((unsigned char)*rec) || /* identifier? */
 			 *rec == '_' || /* also identifier? */
@@ -174,10 +172,12 @@ int xdl_emit_diff(xdfenv_t *xe, xdchange_t *xscr, xdemitcb_t *ecb,
 	struct func_line func_line = { 0 };
 
 	for (xch = xscr; xch; xch = xche->next) {
+		xdchange_t *xchp = xch;
 		xche = xdl_get_hunk(&xch, xecfg);
 		if (!xch)
 			break;
 
+pre_context_calculation:
 		s1 = XDL_MAX(xch->i1 - xecfg->ctxlen, 0);
 		s2 = XDL_MAX(xch->i2 - xecfg->ctxlen, 0);
 
@@ -212,8 +212,23 @@ int xdl_emit_diff(xdfenv_t *xe, xdchange_t *xscr, xdemitcb_t *ecb,
 			if (fs1 < 0)
 				fs1 = 0;
 			if (fs1 < s1) {
-				s2 -= s1 - fs1;
+				s2 = XDL_MAX(s2 - (s1 - fs1), 0);
 				s1 = fs1;
+
+				/*
+				 * Did we extend context upwards into an
+				 * ignored change?
+				 */
+				while (xchp != xch &&
+				       xchp->i1 + xchp->chg1 <= s1 &&
+				       xchp->i2 + xchp->chg2 <= s2)
+					xchp = xchp->next;
+
+				/* If so, show it after all. */
+				if (xchp != xch) {
+					xch = xchp;
+					goto pre_context_calculation;
+				}
 			}
 		}
 
@@ -234,7 +249,7 @@ int xdl_emit_diff(xdfenv_t *xe, xdchange_t *xscr, xdemitcb_t *ecb,
 			if (fe1 < 0)
 				fe1 = xe->xdf1.nrec;
 			if (fe1 > e1) {
-				e2 += fe1 - e1;
+				e2 = XDL_MIN(e2 + (fe1 - e1), xe->xdf2.nrec);
 				e1 = fe1;
 			}
 
@@ -263,7 +278,8 @@ int xdl_emit_diff(xdfenv_t *xe, xdchange_t *xscr, xdemitcb_t *ecb,
 				      s1 - 1, funclineprev);
 			funclineprev = s1 - 1;
 		}
-		if (xdl_emit_hunk_hdr(s1 + 1, e1 - s1, s2 + 1, e2 - s2,
+		if (!(xecfg->flags & XDL_EMIT_NO_HUNK_HDR) &&
+		    xdl_emit_hunk_hdr(s1 + 1, e1 - s1, s2 + 1, e2 - s2,
 				      func_line.buf, func_line.len, ecb) < 0)
 			return -1;
 
diff --git a/src/xdiff/xhistogram.c b/src/xdiff/xhistogram.c
index 00bbfcec4..80794748b 100644
--- a/src/xdiff/xhistogram.c
+++ b/src/xdiff/xhistogram.c
@@ -42,8 +42,6 @@
  */
 
 #include "xinclude.h"
-#include "xtypes.h"
-#include "xdiff.h"
 
 #define MAX_PTR	UINT_MAX
 #define MAX_CNT	UINT_MAX
@@ -90,27 +88,21 @@ struct region {
 #define REC(env, s, l) \
 	(env->xdf##s.recs[l - 1])
 
-static int cmp_recs(xpparam_t const *xpp,
-	xrecord_t *r1, xrecord_t *r2)
+static int cmp_recs(xrecord_t *r1, xrecord_t *r2)
 {
-	return r1->ha == r2->ha &&
-		xdl_recmatch(r1->ptr, r1->size, r2->ptr, r2->size,
-			    xpp->flags);
-}
+	return r1->ha == r2->ha;
 
-#define CMP_ENV(xpp, env, s1, l1, s2, l2) \
-	(cmp_recs(xpp, REC(env, s1, l1), REC(env, s2, l2)))
+}
 
 #define CMP(i, s1, l1, s2, l2) \
-	(cmp_recs(i->xpp, REC(i->env, s1, l1), REC(i->env, s2, l2)))
+	(cmp_recs(REC(i->env, s1, l1), REC(i->env, s2, l2)))
 
 #define TABLE_HASH(index, side, line) \
 	XDL_HASHLONG((REC(index->env, side, line))->ha, index->table_bits)
 
-static int scanA(struct histindex *index, unsigned int line1, unsigned int count1)
+static int scanA(struct histindex *index, int line1, int count1)
 {
-	unsigned int ptr;
-	unsigned int tbl_idx;
+	unsigned int ptr, tbl_idx;
 	unsigned int chain_len;
 	struct record **rec_chain, *rec;
 
@@ -161,10 +153,8 @@ continue_scan:
 	return 0;
 }
 
-static int try_lcs(
-	struct histindex *index, struct region *lcs, unsigned int b_ptr,
-	unsigned int line1, unsigned int count1,
-	unsigned int line2, unsigned int count2)
+static int try_lcs(struct histindex *index, struct region *lcs, int b_ptr,
+	int line1, int count1, int line2, int count2)
 {
 	unsigned int b_next = b_ptr + 1;
 	struct record *rec = index->records[TABLE_HASH(index, 2, b_ptr)];
@@ -236,59 +226,33 @@ static int try_lcs(
 	return b_next;
 }
 
-static int find_lcs(
-	struct histindex *index, struct region *lcs,
-	unsigned int line1, unsigned int count1,
-	unsigned int line2, unsigned int count2)
+static int fall_back_to_classic_diff(xpparam_t const *xpp, xdfenv_t *env,
+		int line1, int count1, int line2, int count2)
 {
-	unsigned int b_ptr;
-
-	if (scanA(index, line1, count1))
-		return -1;
-
-	index->cnt = index->max_chain_length + 1;
+	xpparam_t xpparam;
 
-	for (b_ptr = line2; b_ptr <= LINE_END(2); )
-		b_ptr = try_lcs(index, lcs, b_ptr, line1, count1, line2, count2);
+	memset(&xpparam, 0, sizeof(xpparam));
+	xpparam.flags = xpp->flags & ~XDF_DIFF_ALGORITHM_MASK;
 
-	return index->has_common && index->max_chain_length < index->cnt;
+	return xdl_fall_back_diff(env, &xpparam,
+				  line1, count1, line2, count2);
 }
 
-static int fall_back_to_classic_diff(struct histindex *index,
-		int line1, int count1, int line2, int count2)
+static inline void free_index(struct histindex *index)
 {
-	xpparam_t xpp;
-	xpp.flags = index->xpp->flags & ~XDF_DIFF_ALGORITHM_MASK;
-
-	return xdl_fall_back_diff(index->env, &xpp,
-				  line1, count1, line2, count2);
+	xdl_free(index->records);
+	xdl_free(index->line_map);
+	xdl_free(index->next_ptrs);
+	xdl_cha_free(&index->rcha);
 }
 
-static int histogram_diff(
-	xpparam_t const *xpp, xdfenv_t *env,
-	unsigned int line1, unsigned int count1,
-	unsigned int line2, unsigned int count2)
+static int find_lcs(xpparam_t const *xpp, xdfenv_t *env,
+		    struct region *lcs,
+		    int line1, int count1, int line2, int count2)
 {
+	int b_ptr;
+	int sz, ret = -1;
 	struct histindex index;
-	struct region lcs;
-	size_t sz;
-	int result = -1;
-
-	if (count1 <= 0 && count2 <= 0)
-		return 0;
-
-	if (LINE_END(1) >= MAX_PTR)
-		return -1;
-
-	if (!count1) {
-		while(count2--)
-			env->xdf2.rchg[line2++ - 1] = 1;
-		return 0;
-	} else if (!count2) {
-		while(count1--)
-			env->xdf1.rchg[line1++ - 1] = 1;
-		return 0;
-	}
 
 	memset(&index, 0, sizeof(index));
 
@@ -302,8 +266,7 @@ static int histogram_diff(
 
 	index.table_bits = xdl_hashbits(count1);
 	sz = index.records_size = 1 << index.table_bits;
-	GIT_ERROR_CHECK_ALLOC_MULTIPLY(&sz, sz, sizeof(struct record *));
-
+	sz *= sizeof(struct record *);
 	if (!(index.records = (struct record **) xdl_malloc(sz)))
 		goto cleanup;
 	memset(index.records, 0, sz);
@@ -327,9 +290,55 @@ static int histogram_diff(
 	index.ptr_shift = line1;
 	index.max_chain_length = 64;
 
+	if (scanA(&index, line1, count1))
+		goto cleanup;
+
+	index.cnt = index.max_chain_length + 1;
+
+	for (b_ptr = line2; b_ptr <= LINE_END(2); )
+		b_ptr = try_lcs(&index, lcs, b_ptr, line1, count1, line2, count2);
+
+	if (index.has_common && index.max_chain_length < index.cnt)
+		ret = 1;
+	else
+		ret = 0;
+
+cleanup:
+	free_index(&index);
+	return ret;
+}
+
+static int histogram_diff(xpparam_t const *xpp, xdfenv_t *env,
+	int line1, int count1, int line2, int count2)
+{
+	struct region lcs;
+	int lcs_found;
+	int result;
+redo:
+	result = -1;
+
+	if (count1 <= 0 && count2 <= 0)
+		return 0;
+
+	if (LINE_END(1) >= MAX_PTR)
+		return -1;
+
+	if (!count1) {
+		while(count2--)
+			env->xdf2.rchg[line2++ - 1] = 1;
+		return 0;
+	} else if (!count2) {
+		while(count1--)
+			env->xdf1.rchg[line1++ - 1] = 1;
+		return 0;
+	}
+
 	memset(&lcs, 0, sizeof(lcs));
-	if (find_lcs(&index, &lcs, line1, count1, line2, count2))
-		result = fall_back_to_classic_diff(&index, line1, count1, line2, count2);
+	lcs_found = find_lcs(xpp, env, &lcs, line1, count1, line2, count2);
+	if (lcs_found < 0)
+		goto out;
+	else if (lcs_found)
+		result = fall_back_to_classic_diff(xpp, env, line1, count1, line2, count2);
 	else {
 		if (lcs.begin1 == 0 && lcs.begin2 == 0) {
 			while (count1--)
@@ -342,21 +351,21 @@ static int histogram_diff(
 						line1, lcs.begin1 - line1,
 						line2, lcs.begin2 - line2);
 			if (result)
-				goto cleanup;
-			result = histogram_diff(xpp, env,
-						lcs.end1 + 1, LINE_END(1) - lcs.end1,
-						lcs.end2 + 1, LINE_END(2) - lcs.end2);
-			if (result)
-				goto cleanup;
+				goto out;
+			/*
+			 * result = histogram_diff(xpp, env,
+			 *            lcs.end1 + 1, LINE_END(1) - lcs.end1,
+			 *            lcs.end2 + 1, LINE_END(2) - lcs.end2);
+			 * but let's optimize tail recursion ourself:
+			*/
+			count1 = LINE_END(1) - lcs.end1;
+			line1 = lcs.end1 + 1;
+			count2 = LINE_END(2) - lcs.end2;
+			line2 = lcs.end2 + 1;
+			goto redo;
 		}
 	}
-
-cleanup:
-	xdl_free(index.records);
-	xdl_free(index.line_map);
-	xdl_free(index.next_ptrs);
-	xdl_cha_free(&index.rcha);
-
+out:
 	return result;
 }
 
diff --git a/src/xdiff/xinclude.h b/src/xdiff/xinclude.h
index 068ce42f8..75db1d8f3 100644
--- a/src/xdiff/xinclude.h
+++ b/src/xdiff/xinclude.h
@@ -23,17 +23,7 @@
 #if !defined(XINCLUDE_H)
 #define XINCLUDE_H
 
-#include <ctype.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-#include <limits.h>
-
-#ifdef _WIN32
-#else
-#include <unistd.h>
-#endif
-
+#include "git-xdiff.h"
 #include "xmacros.h"
 #include "xdiff.h"
 #include "xtypes.h"
@@ -42,6 +32,5 @@
 #include "xdiffi.h"
 #include "xemit.h"
 
-#include "common.h"
 
 #endif /* #if !defined(XINCLUDE_H) */
diff --git a/src/xdiff/xmerge.c b/src/xdiff/xmerge.c
index 278cbe124..fff0b594f 100644
--- a/src/xdiff/xmerge.c
+++ b/src/xdiff/xmerge.c
@@ -109,53 +109,44 @@ static int xdl_merge_cmp_lines(xdfenv_t *xe1, int i1, xdfenv_t *xe2, int i2,
 	return 0;
 }
 
-static int xdl_recs_copy_0(size_t *out, int use_orig, xdfenv_t *xe, int i, int count, int needs_cr, int add_nl, char *dest)
+static int xdl_recs_copy_0(int use_orig, xdfenv_t *xe, int i, int count, int needs_cr, int add_nl, char *dest)
 {
 	xrecord_t **recs;
-	size_t size = 0;
-
-	*out = 0;
+	int size = 0;
 
 	recs = (use_orig ? xe->xdf1.recs : xe->xdf2.recs) + i;
 
 	if (count < 1)
 		return 0;
 
-	for (i = 0; i < count; ) {
+	for (i = 0; i < count; size += recs[i++]->size)
 		if (dest)
 			memcpy(dest + size, recs[i]->ptr, recs[i]->size);
-
-		GIT_ERROR_CHECK_ALLOC_ADD(&size, size, recs[i++]->size);
-	}
-
 	if (add_nl) {
 		i = recs[count - 1]->size;
 		if (i == 0 || recs[count - 1]->ptr[i - 1] != '\n') {
 			if (needs_cr) {
 				if (dest)
 					dest[size] = '\r';
-				GIT_ERROR_CHECK_ALLOC_ADD(&size, size, 1);
+				size++;
 			}
 
 			if (dest)
 				dest[size] = '\n';
-
-			GIT_ERROR_CHECK_ALLOC_ADD(&size, size, 1);
+			size++;
 		}
 	}
-
-	*out = size;
-	return 0;
+	return size;
 }
 
-static int xdl_recs_copy(size_t *out, xdfenv_t *xe, int i, int count, int needs_cr, int add_nl, char *dest)
+static int xdl_recs_copy(xdfenv_t *xe, int i, int count, int needs_cr, int add_nl, char *dest)
 {
-	return xdl_recs_copy_0(out, 0, xe, i, count, needs_cr, add_nl, dest);
+	return xdl_recs_copy_0(0, xe, i, count, needs_cr, add_nl, dest);
 }
 
-static int xdl_orig_copy(size_t *out, xdfenv_t *xe, int i, int count, int needs_cr, int add_nl, char *dest)
+static int xdl_orig_copy(xdfenv_t *xe, int i, int count, int needs_cr, int add_nl, char *dest)
 {
-	return xdl_recs_copy_0(out, 1, xe, i, count, needs_cr, add_nl, dest);
+	return xdl_recs_copy_0(1, xe, i, count, needs_cr, add_nl, dest);
 }
 
 /*
@@ -202,32 +193,26 @@ static int is_cr_needed(xdfenv_t *xe1, xdfenv_t *xe2, xdmerge_t *m)
 	return needs_cr < 0 ? 0 : needs_cr;
 }
 
-static int fill_conflict_hunk(size_t *out, xdfenv_t *xe1, const char *name1,
+static int fill_conflict_hunk(xdfenv_t *xe1, const char *name1,
 			      xdfenv_t *xe2, const char *name2,
 			      const char *name3,
-			      size_t size, int i, int style,
+			      int size, int i, int style,
 			      xdmerge_t *m, char *dest, int marker_size)
 {
-	int marker1_size = (name1 ? (int)strlen(name1) + 1 : 0);
-	int marker2_size = (name2 ? (int)strlen(name2) + 1 : 0);
-	int marker3_size = (name3 ? (int)strlen(name3) + 1 : 0);
+	int marker1_size = (name1 ? strlen(name1) + 1 : 0);
+	int marker2_size = (name2 ? strlen(name2) + 1 : 0);
+	int marker3_size = (name3 ? strlen(name3) + 1 : 0);
 	int needs_cr = is_cr_needed(xe1, xe2, m);
-	size_t copied;
-
-	*out = 0;
 
 	if (marker_size <= 0)
 		marker_size = DEFAULT_CONFLICT_MARKER_SIZE;
 
 	/* Before conflicting part */
-	if (xdl_recs_copy(&copied, xe1, i, m->i1 - i, 0, 0,
-			      dest ? dest + size : NULL) < 0)
-		return -1;
-
-	GIT_ERROR_CHECK_ALLOC_ADD(&size, size, copied);
+	size += xdl_recs_copy(xe1, i, m->i1 - i, 0, 0,
+			      dest ? dest + size : NULL);
 
 	if (!dest) {
-		GIT_ERROR_CHECK_ALLOC_ADD5(&size, size, marker_size, 1, needs_cr,  marker1_size);
+		size += marker_size + 1 + needs_cr + marker1_size;
 	} else {
 		memset(dest + size, '<', marker_size);
 		size += marker_size;
@@ -242,16 +227,13 @@ static int fill_conflict_hunk(size_t *out, xdfenv_t *xe1, const char *name1,
 	}
 
 	/* Postimage from side #1 */
-	if (xdl_recs_copy(&copied, xe1, m->i1, m->chg1, needs_cr, 1,
-			      dest ? dest + size : NULL) < 0)
-		return -1;
+	size += xdl_recs_copy(xe1, m->i1, m->chg1, needs_cr, 1,
+			      dest ? dest + size : NULL);
 
-	GIT_ERROR_CHECK_ALLOC_ADD(&size, size, copied);
-
-	if (style == XDL_MERGE_DIFF3) {
+	if (style == XDL_MERGE_DIFF3 || style == XDL_MERGE_ZEALOUS_DIFF3) {
 		/* Shared preimage */
 		if (!dest) {
-			GIT_ERROR_CHECK_ALLOC_ADD5(&size, size, marker_size, 1, needs_cr, marker3_size);
+			size += marker_size + 1 + needs_cr + marker3_size;
 		} else {
 			memset(dest + size, '|', marker_size);
 			size += marker_size;
@@ -264,15 +246,12 @@ static int fill_conflict_hunk(size_t *out, xdfenv_t *xe1, const char *name1,
 				dest[size++] = '\r';
 			dest[size++] = '\n';
 		}
-
-		if (xdl_orig_copy(&copied, xe1, m->i0, m->chg0, needs_cr, 1,
-				      dest ? dest + size : NULL) < 0)
-			return -1;
-		GIT_ERROR_CHECK_ALLOC_ADD(&size, size, copied);
+		size += xdl_orig_copy(xe1, m->i0, m->chg0, needs_cr, 1,
+				      dest ? dest + size : NULL);
 	}
 
 	if (!dest) {
-		GIT_ERROR_CHECK_ALLOC_ADD4(&size, size, marker_size, 1, needs_cr);
+		size += marker_size + 1 + needs_cr;
 	} else {
 		memset(dest + size, '=', marker_size);
 		size += marker_size;
@@ -282,14 +261,10 @@ static int fill_conflict_hunk(size_t *out, xdfenv_t *xe1, const char *name1,
 	}
 
 	/* Postimage from side #2 */
-
-	if (xdl_recs_copy(&copied, xe2, m->i2, m->chg2, needs_cr, 1,
-			      dest ? dest + size : NULL) < 0)
-		return -1;
-	GIT_ERROR_CHECK_ALLOC_ADD(&size, size, copied);
-
+	size += xdl_recs_copy(xe2, m->i2, m->chg2, needs_cr, 1,
+			      dest ? dest + size : NULL);
 	if (!dest) {
-		GIT_ERROR_CHECK_ALLOC_ADD5(&size, size, marker_size, 1, needs_cr, marker2_size);
+		size += marker_size + 1 + needs_cr + marker2_size;
 	} else {
 		memset(dest + size, '>', marker_size);
 		size += marker_size;
@@ -302,71 +277,83 @@ static int fill_conflict_hunk(size_t *out, xdfenv_t *xe1, const char *name1,
 			dest[size++] = '\r';
 		dest[size++] = '\n';
 	}
-
-	*out = size;
-	return 0;
+	return size;
 }
 
-static int xdl_fill_merge_buffer(size_t *out,
-				 xdfenv_t *xe1, const char *name1,
+static int xdl_fill_merge_buffer(xdfenv_t *xe1, const char *name1,
 				 xdfenv_t *xe2, const char *name2,
 				 const char *ancestor_name,
 				 int favor,
 				 xdmerge_t *m, char *dest, int style,
 				 int marker_size)
 {
-	size_t size, copied;
-	int i;
-
-	*out = 0;
+	int size, i;
 
 	for (size = i = 0; m; m = m->next) {
 		if (favor && !m->mode)
 			m->mode = favor;
 
-		if (m->mode == 0) {
-			if (fill_conflict_hunk(&size, xe1, name1, xe2, name2,
+		if (m->mode == 0)
+			size = fill_conflict_hunk(xe1, name1, xe2, name2,
 						  ancestor_name,
 						  size, i, style, m, dest,
-						  marker_size) < 0)
-				return -1;
-		}
+						  marker_size);
 		else if (m->mode & 3) {
 			/* Before conflicting part */
-			if (xdl_recs_copy(&copied, xe1, i, m->i1 - i, 0, 0,
-					      dest ? dest + size : NULL) < 0)
-				return -1;
-			GIT_ERROR_CHECK_ALLOC_ADD(&size, size, copied);
-
+			size += xdl_recs_copy(xe1, i, m->i1 - i, 0, 0,
+					      dest ? dest + size : NULL);
 			/* Postimage from side #1 */
 			if (m->mode & 1) {
 				int needs_cr = is_cr_needed(xe1, xe2, m);
 
-				if (xdl_recs_copy(&copied, xe1, m->i1, m->chg1, needs_cr, (m->mode & 2),
-						      dest ? dest + size : NULL) < 0)
-					return -1;
-				GIT_ERROR_CHECK_ALLOC_ADD(&size, size, copied);
+				size += xdl_recs_copy(xe1, m->i1, m->chg1, needs_cr, (m->mode & 2),
+						      dest ? dest + size : NULL);
 			}
-
 			/* Postimage from side #2 */
-			if (m->mode & 2) {
-				if (xdl_recs_copy(&copied, xe2, m->i2, m->chg2, 0, 0,
-						      dest ? dest + size : NULL) < 0)
-					return -1;
-				GIT_ERROR_CHECK_ALLOC_ADD(&size, size, copied);
-			}
+			if (m->mode & 2)
+				size += xdl_recs_copy(xe2, m->i2, m->chg2, 0, 0,
+						      dest ? dest + size : NULL);
 		} else
 			continue;
 		i = m->i1 + m->chg1;
 	}
+	size += xdl_recs_copy(xe1, i, xe1->xdf2.nrec - i, 0, 0,
+			      dest ? dest + size : NULL);
+	return size;
+}
 
-	if (xdl_recs_copy(&copied, xe1, i, xe1->xdf2.nrec - i, 0, 0,
-			      dest ? dest + size : NULL) < 0)
-		return -1;
-	GIT_ERROR_CHECK_ALLOC_ADD(&size, size, copied);
+static int recmatch(xrecord_t *rec1, xrecord_t *rec2, unsigned long flags)
+{
+	return xdl_recmatch(rec1->ptr, rec1->size,
+			    rec2->ptr, rec2->size, flags);
+}
 
-	*out = size;
-	return 0;
+/*
+ * Remove any common lines from the beginning and end of the conflicted region.
+ */
+static void xdl_refine_zdiff3_conflicts(xdfenv_t *xe1, xdfenv_t *xe2, xdmerge_t *m,
+		xpparam_t const *xpp)
+{
+	xrecord_t **rec1 = xe1->xdf2.recs, **rec2 = xe2->xdf2.recs;
+	for (; m; m = m->next) {
+		/* let's handle just the conflicts */
+		if (m->mode)
+			continue;
+
+		while(m->chg1 && m->chg2 &&
+		      recmatch(rec1[m->i1], rec2[m->i2], xpp->flags)) {
+			m->chg1--;
+			m->chg2--;
+			m->i1++;
+			m->i2++;
+		}
+		while (m->chg1 && m->chg2 &&
+		       recmatch(rec1[m->i1 + m->chg1 - 1],
+				rec2[m->i2 + m->chg2 - 1], xpp->flags)) {
+			m->chg1--;
+			m->chg2--;
+		}
+	}
 }
 
 /*
@@ -529,7 +516,22 @@ static int xdl_do_merge(xdfenv_t *xe1, xdchange_t *xscr1,
 	int style = xmp->style;
 	int favor = xmp->favor;
 
-	if (style == XDL_MERGE_DIFF3) {
+	/*
+	 * XDL_MERGE_DIFF3 does not attempt to refine conflicts by looking
+	 * at common areas of sides 1 & 2, because the base (side 0) does
+	 * not match and is being shown.  Similarly, simplification of
+	 * non-conflicts is also skipped due to the skipping of conflict
+	 * refinement.
+	 *
+	 * XDL_MERGE_ZEALOUS_DIFF3, on the other hand, will attempt to
+	 * refine conflicts looking for common areas of sides 1 & 2.
+	 * However, since the base is being shown and does not match,
+	 * it will only look for common areas at the beginning or end
+	 * of the conflict block.  Since XDL_MERGE_ZEALOUS_DIFF3's
+	 * conflict refinement is much more limited in this fashion, the
+	 * conflict simplification will be skipped.
+	 */
+	if (style == XDL_MERGE_DIFF3 || style == XDL_MERGE_ZEALOUS_DIFF3) {
 		/*
 		 * "diff3 -m" output does not make sense for anything
 		 * more aggressive than XDL_MERGE_EAGER.
@@ -650,34 +652,31 @@ static int xdl_do_merge(xdfenv_t *xe1, xdchange_t *xscr1,
 	if (!changes)
 		changes = c;
 	/* refine conflicts */
-	if (XDL_MERGE_ZEALOUS <= level &&
-	    (xdl_refine_conflicts(xe1, xe2, changes, xpp) < 0 ||
-	     xdl_simplify_non_conflicts(xe1, changes,
-					XDL_MERGE_ZEALOUS < level) < 0)) {
+	if (style == XDL_MERGE_ZEALOUS_DIFF3) {
+		xdl_refine_zdiff3_conflicts(xe1, xe2, changes, xpp);
+	} else if (XDL_MERGE_ZEALOUS <= level &&
+		   (xdl_refine_conflicts(xe1, xe2, changes, xpp) < 0 ||
+		    xdl_simplify_non_conflicts(xe1, changes,
+					       XDL_MERGE_ZEALOUS < level) < 0)) {
 		xdl_cleanup_merge(changes);
 		return -1;
 	}
 	/* output */
 	if (result) {
 		int marker_size = xmp->marker_size;
-		size_t size;
-
-		if (xdl_fill_merge_buffer(&size, xe1, name1, xe2, name2,
+		int size = xdl_fill_merge_buffer(xe1, name1, xe2, name2,
 						 ancestor_name,
 						 favor, changes, NULL, style,
-						 marker_size) < 0)
-			return -1;
-
+						 marker_size);
 		result->ptr = xdl_malloc(size);
 		if (!result->ptr) {
 			xdl_cleanup_merge(changes);
 			return -1;
 		}
 		result->size = size;
-		if (xdl_fill_merge_buffer(&size, xe1, name1, xe2, name2,
+		xdl_fill_merge_buffer(xe1, name1, xe2, name2,
 				      ancestor_name, favor, changes,
-				      result->ptr, style, marker_size) < 0)
-			return -1;
+				      result->ptr, style, marker_size);
 	}
 	return xdl_cleanup_merge(changes);
 }
@@ -717,22 +716,10 @@ int xdl_merge(mmfile_t *orig, mmfile_t *mf1, mmfile_t *mf2,
 	status = 0;
 	if (!xscr1) {
 		result->ptr = xdl_malloc(mf2->size);
-		if (!result->ptr) {
-			xdl_free_script(xscr2);
-			xdl_free_env(&xe1);
-			xdl_free_env(&xe2);
-			return -1;
-		}
 		memcpy(result->ptr, mf2->ptr, mf2->size);
 		result->size = mf2->size;
 	} else if (!xscr2) {
 		result->ptr = xdl_malloc(mf1->size);
-		if (!result->ptr) {
-			xdl_free_script(xscr1);
-			xdl_free_env(&xe1);
-			xdl_free_env(&xe2);
-			return -1;
-		}
 		memcpy(result->ptr, mf1->ptr, mf1->size);
 		result->size = mf1->size;
 	} else {
diff --git a/src/xdiff/xpatience.c b/src/xdiff/xpatience.c
index 53b7d5fd1..c5d48e80a 100644
--- a/src/xdiff/xpatience.c
+++ b/src/xdiff/xpatience.c
@@ -20,8 +20,6 @@
  *
  */
 #include "xinclude.h"
-#include "xtypes.h"
-#include "xdiff.h"
 
 /*
  * The basic idea of patience diff is to find lines that are unique in
@@ -78,7 +76,7 @@ struct hashmap {
 
 static int is_anchor(xpparam_t const *xpp, const char *line)
 {
-	unsigned long i;
+	int i;
 	for (i = 0; i < xpp->anchors_nr; i++) {
 		if (!strncmp(line, xpp->anchors[i], strlen(xpp->anchors[i])))
 			return 1;
@@ -92,7 +90,7 @@ static void insert_record(xpparam_t const *xpp, int line, struct hashmap *map,
 {
 	xrecord_t **records = pass == 1 ?
 		map->env->xdf1.recs : map->env->xdf2.recs;
-	xrecord_t *record = records[line - 1], *other;
+	xrecord_t *record = records[line - 1];
 	/*
 	 * After xdl_prepare_env() (or more precisely, due to
 	 * xdl_classify_record()), the "ha" member of the records (AKA lines)
@@ -106,11 +104,7 @@ static void insert_record(xpparam_t const *xpp, int line, struct hashmap *map,
 	int index = (int)((record->ha << 1) % map->alloc);
 
 	while (map->entries[index].line1) {
-		other = map->env->xdf1.recs[map->entries[index].line1 - 1];
-		if (map->entries[index].hash != record->ha ||
-				!xdl_recmatch(record->ptr, record->size,
-					other->ptr, other->size,
-					map->xpp->flags)) {
+		if (map->entries[index].hash != record->ha) {
 			if (++index >= map->alloc)
 				index = 0;
 			continue;
@@ -217,9 +211,6 @@ static struct entry *find_longest_common_sequence(struct hashmap *map)
 	 */
 	int anchor_i = -1;
 
-	if (!sequence)
-		return NULL;
-
 	for (entry = map->first; entry; entry = entry->next) {
 		if (!entry->line2 || entry->line2 == NON_UNIQUE)
 			continue;
@@ -258,8 +249,7 @@ static int match(struct hashmap *map, int line1, int line2)
 {
 	xrecord_t *record1 = map->env->xdf1.recs[line1 - 1];
 	xrecord_t *record2 = map->env->xdf2.recs[line2 - 1];
-	return xdl_recmatch(record1->ptr, record1->size,
-		record2->ptr, record2->size, map->xpp->flags);
+	return record1->ha == record2->ha;
 }
 
 static int patience_diff(mmfile_t *file1, mmfile_t *file2,
@@ -294,9 +284,6 @@ static int walk_common_sequence(struct hashmap *map, struct entry *first,
 
 		/* Recurse */
 		if (next1 > line1 || next2 > line2) {
-			struct hashmap submap;
-
-			memset(&submap, 0, sizeof(submap));
 			if (patience_diff(map->file1, map->file2,
 					map->xpp, map->env,
 					line1, next1 - line1,
@@ -323,6 +310,8 @@ static int fall_back_to_classic_diff(struct hashmap *map,
 		int line1, int count1, int line2, int count2)
 {
 	xpparam_t xpp;
+
+	memset(&xpp, 0, sizeof(xpp));
 	xpp.flags = map->xpp->flags & ~XDF_DIFF_ALGORITHM_MASK;
 
 	return xdl_fall_back_diff(map->env, &xpp,
diff --git a/src/xdiff/xprepare.c b/src/xdiff/xprepare.c
index abeb8fb84..4527a4a07 100644
--- a/src/xdiff/xprepare.c
+++ b/src/xdiff/xprepare.c
@@ -181,15 +181,11 @@ static int xdl_prepare_ctx(unsigned int pass, mmfile_t *mf, long narec, xpparam_
 	if (!(recs = (xrecord_t **) xdl_malloc(narec * sizeof(xrecord_t *))))
 		goto abort;
 
-	if (XDF_DIFF_ALG(xpp->flags) == XDF_HISTOGRAM_DIFF)
-		hbits = hsize = 0;
-	else {
-		hbits = xdl_hashbits((unsigned int) narec);
-		hsize = 1 << hbits;
-		if (!(rhash = (xrecord_t **) xdl_malloc(hsize * sizeof(xrecord_t *))))
-			goto abort;
-		memset(rhash, 0, hsize * sizeof(xrecord_t *));
-	}
+	hbits = xdl_hashbits((unsigned int) narec);
+	hsize = 1 << hbits;
+	if (!(rhash = (xrecord_t **) xdl_malloc(hsize * sizeof(xrecord_t *))))
+		goto abort;
+	memset(rhash, 0, hsize * sizeof(xrecord_t *));
 
 	nrec = 0;
 	if ((cur = blk = xdl_mmfile_first(mf, &bsize)) != NULL) {
@@ -208,9 +204,7 @@ static int xdl_prepare_ctx(unsigned int pass, mmfile_t *mf, long narec, xpparam_
 			crec->size = (long) (cur - prev);
 			crec->ha = hav;
 			recs[nrec++] = crec;
-
-			if ((XDF_DIFF_ALG(xpp->flags) != XDF_HISTOGRAM_DIFF) &&
-			    xdl_classify_record(pass, cf, rhash, hbits, crec) < 0)
+			if (xdl_classify_record(pass, cf, rhash, hbits, crec) < 0)
 				goto abort;
 		}
 	}
@@ -219,10 +213,13 @@ static int xdl_prepare_ctx(unsigned int pass, mmfile_t *mf, long narec, xpparam_
 		goto abort;
 	memset(rchg, 0, (nrec + 2) * sizeof(char));
 
-	if (!(rindex = (long *) xdl_malloc((nrec + 1) * sizeof(long))))
-		goto abort;
-	if (!(ha = (unsigned long *) xdl_malloc((nrec + 1) * sizeof(unsigned long))))
-		goto abort;
+	if ((XDF_DIFF_ALG(xpp->flags) != XDF_PATIENCE_DIFF) &&
+	    (XDF_DIFF_ALG(xpp->flags) != XDF_HISTOGRAM_DIFF)) {
+		if (!(rindex = xdl_malloc((nrec + 1) * sizeof(*rindex))))
+			goto abort;
+		if (!(ha = xdl_malloc((nrec + 1) * sizeof(*ha))))
+			goto abort;
+	}
 
 	xdf->nrec = nrec;
 	xdf->recs = recs;
@@ -279,8 +276,7 @@ int xdl_prepare_env(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
 	enl1 = xdl_guess_lines(mf1, sample) + 1;
 	enl2 = xdl_guess_lines(mf2, sample) + 1;
 
-	if (XDF_DIFF_ALG(xpp->flags) != XDF_HISTOGRAM_DIFF &&
-	    xdl_init_classifier(&cf, enl1 + enl2 + 1, xpp->flags) < 0)
+	if (xdl_init_classifier(&cf, enl1 + enl2 + 1, xpp->flags) < 0)
 		return -1;
 
 	if (xdl_prepare_ctx(1, mf1, enl1, xpp, &cf, &xe->xdf1) < 0) {
@@ -305,8 +301,7 @@ int xdl_prepare_env(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
 		return -1;
 	}
 
-	if (XDF_DIFF_ALG(xpp->flags) != XDF_HISTOGRAM_DIFF)
-		xdl_free_classifier(&cf);
+	xdl_free_classifier(&cf);
 
 	return 0;
 }
diff --git a/src/xdiff/xutils.c b/src/xdiff/xutils.c
index 17c9ae184..cfa6e2220 100644
--- a/src/xdiff/xutils.c
+++ b/src/xdiff/xutils.c
@@ -23,8 +23,6 @@
 #include "xinclude.h"
 
 
-
-
 long xdl_bogosqrt(long n) {
 	long i;
 
@@ -52,7 +50,7 @@ int xdl_emit_diffrec(char const *rec, long size, char const *pre, long psize,
 		mb[2].size = strlen(mb[2].ptr);
 		i++;
 	}
-	if (ecb->outf(ecb->priv, mb, i) < 0) {
+	if (ecb->out_line(ecb->priv, mb, i) < 0) {
 
 		return -1;
 	}
@@ -342,8 +340,9 @@ int xdl_num_out(char *out, long val) {
 	return str - out;
 }
 
-int xdl_emit_hunk_hdr(long s1, long c1, long s2, long c2,
-		      const char *func, long funclen, xdemitcb_t *ecb) {
+static int xdl_format_hunk_hdr(long s1, long c1, long s2, long c2,
+			       const char *func, long funclen,
+			       xdemitcb_t *ecb) {
 	int nb = 0;
 	mmbuffer_t mb;
 	char buf[128];
@@ -376,7 +375,7 @@ int xdl_emit_hunk_hdr(long s1, long c1, long s2, long c2,
 	nb += 3;
 	if (func && funclen) {
 		buf[nb++] = ' ';
-		if (funclen > (long)(sizeof(buf) - nb - 1))
+		if (funclen > sizeof(buf) - nb - 1)
 			funclen = sizeof(buf) - nb - 1;
 		memcpy(buf + nb, func, funclen);
 		nb += funclen;
@@ -385,9 +384,21 @@ int xdl_emit_hunk_hdr(long s1, long c1, long s2, long c2,
 
 	mb.ptr = buf;
 	mb.size = nb;
-	if (ecb->outf(ecb->priv, &mb, 1) < 0)
+	if (ecb->out_line(ecb->priv, &mb, 1) < 0)
 		return -1;
+	return 0;
+}
 
+int xdl_emit_hunk_hdr(long s1, long c1, long s2, long c2,
+		      const char *func, long funclen,
+		      xdemitcb_t *ecb) {
+	if (!ecb->out_hunk)
+		return xdl_format_hunk_hdr(s1, c1, s2, c2, func, funclen, ecb);
+	if (ecb->out_hunk(ecb->priv,
+			  c1 ? s1 : s1 - 1, c1,
+			  c2 ? s2 : s2 - 1, c2,
+			  func, funclen) < 0)
+		return -1;
 	return 0;
 }
 
diff --git a/tests/merge/conflict_data.h b/tests/merge/conflict_data.h
index 27f19c1b0..0b1e7ee03 100644
--- a/tests/merge/conflict_data.h
+++ b/tests/merge/conflict_data.h
@@ -36,6 +36,15 @@
 	"this file is changed in branch and master\n" \
 	">>>>>>> 7cb63eed597130ba4abb87b3e544b85021905520\n"
 
+#define CONFLICTING_ZDIFF3_FILE \
+	"<<<<<<< HEAD\n" \
+	"this file is changed in master and branch\n" \
+	"||||||| initial\n" \
+	"this file is a conflict\n" \
+	"=======\n" \
+	"this file is changed in branch and master\n" \
+	">>>>>>> 7cb63eed597130ba4abb87b3e544b85021905520\n"
+
 #define CONFLICTING_UNION_FILE \
 	"this file is changed in master and branch\n" \
 	"this file is changed in branch and master\n"
diff --git a/tests/merge/files.c b/tests/merge/files.c
index fbc54e11e..6296f3b7b 100644
--- a/tests/merge/files.c
+++ b/tests/merge/files.c
@@ -424,3 +424,42 @@ void test_merge_files__crlf_conflict_markers_for_crlf_files(void)
 	cl_assert(memcmp(expected_diff3, result.ptr, expected_len) == 0);
 	git_merge_file_result_free(&result);
 }
+
+void test_merge_files__conflicts_in_zdiff3(void)
+{
+	git_merge_file_input ancestor = GIT_MERGE_FILE_INPUT_INIT,
+		ours = GIT_MERGE_FILE_INPUT_INIT,
+		theirs = GIT_MERGE_FILE_INPUT_INIT;
+	git_merge_file_options opts = GIT_MERGE_FILE_OPTIONS_INIT;
+	git_merge_file_result result = {0};
+
+	const char *expected_zdiff3 =
+		"1,\nfoo,\nbar,\n" \
+		"<<<<<<< file.txt\n" \
+		"||||||| file.txt\n# add more here\n" \
+		"=======\nquux,\nwoot,\n" \
+		">>>>>>> file.txt\nbaz,\n3,\n";
+	size_t expected_zdiff3_len = strlen(expected_zdiff3);
+
+	ancestor.ptr = "1,\n# add more here\n3,\n";
+	ancestor.size = strlen(ancestor.ptr);
+	ancestor.path = "file.txt";
+	ancestor.mode = 0100644;
+
+	ours.ptr = "1,\nfoo,\nbar,\nbaz,\n3,\n";
+	ours.size = strlen(ours.ptr);
+	ours.path = "file.txt";
+	ours.mode = 0100644;
+
+	theirs.ptr = "1,\nfoo,\nbar,\nquux,\nwoot,\nbaz,\n3,\n";
+	theirs.size = strlen(theirs.ptr);
+	theirs.path = "file.txt";
+	theirs.mode = 0100644;
+
+	opts.flags |= GIT_MERGE_FILE_STYLE_ZDIFF3;
+	cl_git_pass(git_merge_file(&result, &ancestor, &ours, &theirs, &opts));
+	cl_assert_equal_i(0, result.automergeable);
+	cl_assert_equal_i(expected_zdiff3_len, result.len);
+	cl_assert(memcmp(expected_zdiff3, result.ptr, expected_zdiff3_len) == 0);
+	git_merge_file_result_free(&result);
+}
diff --git a/tests/merge/workdir/simple.c b/tests/merge/workdir/simple.c
index f51ff09a7..0b672d6a0 100644
--- a/tests/merge/workdir/simple.c
+++ b/tests/merge/workdir/simple.c
@@ -323,6 +323,42 @@ void test_merge_workdir_simple__diff3(void)
 	cl_assert(merge_test_reuc(repo_index, merge_reuc_entries, 3));
 }
 
+void test_merge_workdir_simple__zdiff3(void)
+{
+	git_str conflicting_buf = GIT_STR_INIT;
+
+	struct merge_index_entry merge_index_entries[] = {
+		ADDED_IN_MASTER_INDEX_ENTRY,
+		AUTOMERGEABLE_INDEX_ENTRY,
+		CHANGED_IN_BRANCH_INDEX_ENTRY,
+		CHANGED_IN_MASTER_INDEX_ENTRY,
+
+		{ 0100644, "d427e0b2e138501a3d15cc376077a3631e15bd46", 1, "conflicting.txt" },
+		{ 0100644, "4e886e602529caa9ab11d71f86634bd1b6e0de10", 2, "conflicting.txt" },
+		{ 0100644, "2bd0a343aeef7a2cf0d158478966a6e587ff3863", 3, "conflicting.txt" },
+
+		UNCHANGED_INDEX_ENTRY,
+	};
+
+	struct merge_reuc_entry merge_reuc_entries[] = {
+		AUTOMERGEABLE_REUC_ENTRY,
+		REMOVED_IN_BRANCH_REUC_ENTRY,
+		REMOVED_IN_MASTER_REUC_ENTRY
+	};
+
+	set_core_autocrlf_to(repo, false);
+
+	merge_simple_branch(0, GIT_CHECKOUT_CONFLICT_STYLE_ZDIFF3);
+
+	cl_git_pass(git_futils_readbuffer(&conflicting_buf,
+		TEST_REPO_PATH "/conflicting.txt"));
+	cl_assert_equal_s(CONFLICTING_ZDIFF3_FILE, conflicting_buf.ptr);
+	git_str_dispose(&conflicting_buf);
+
+	cl_assert(merge_test_index(repo_index, merge_index_entries, 8));
+	cl_assert(merge_test_reuc(repo_index, merge_reuc_entries, 3));
+}
+
 void test_merge_workdir_simple__union(void)
 {
 	git_str conflicting_buf = GIT_STR_INIT;
@@ -436,6 +472,48 @@ void test_merge_workdir_simple__diff3_from_config(void)
 	git_config_free(config);
 }
 
+void test_merge_workdir_simple__zdiff3_from_config(void)
+{
+	git_config *config;
+	git_str conflicting_buf = GIT_STR_INIT;
+
+	struct merge_index_entry merge_index_entries[] = {
+		ADDED_IN_MASTER_INDEX_ENTRY,
+		AUTOMERGEABLE_INDEX_ENTRY,
+		CHANGED_IN_BRANCH_INDEX_ENTRY,
+		CHANGED_IN_MASTER_INDEX_ENTRY,
+
+		{ 0100644, "d427e0b2e138501a3d15cc376077a3631e15bd46", 1, "conflicting.txt" },
+		{ 0100644, "4e886e602529caa9ab11d71f86634bd1b6e0de10", 2, "conflicting.txt" },
+		{ 0100644, "2bd0a343aeef7a2cf0d158478966a6e587ff3863", 3, "conflicting.txt" },
+
+		UNCHANGED_INDEX_ENTRY,
+	};
+
+	struct merge_reuc_entry merge_reuc_entries[] = {
+		AUTOMERGEABLE_REUC_ENTRY,
+		REMOVED_IN_BRANCH_REUC_ENTRY,
+		REMOVED_IN_MASTER_REUC_ENTRY
+	};
+
+	cl_git_pass(git_repository_config(&config, repo));
+	cl_git_pass(git_config_set_string(config, "merge.conflictstyle", "zdiff3"));
+
+	set_core_autocrlf_to(repo, false);
+
+	merge_simple_branch(0, 0);
+
+	cl_git_pass(git_futils_readbuffer(&conflicting_buf,
+		TEST_REPO_PATH "/conflicting.txt"));
+	cl_assert(strcmp(conflicting_buf.ptr, CONFLICTING_ZDIFF3_FILE) == 0);
+	git_str_dispose(&conflicting_buf);
+
+	cl_assert(merge_test_index(repo_index, merge_index_entries, 8));
+	cl_assert(merge_test_reuc(repo_index, merge_reuc_entries, 3));
+
+	git_config_free(config);
+}
+
 void test_merge_workdir_simple__merge_overrides_config(void)
 {
 	git_config *config;