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teach --histogram to diff

Port JGit's HistogramDiff algorithm over to C. Rough numbers (TODO) show
that it is faster than its --patience cousin, as well as the default
Meyers algorithm.

The implementation has been reworked to use structs and pointers,
instead of bitmasks, thus doing away with JGit's 2^28 line limit.

We also use xdiff's default hash table implementation (xdl_hash_bits()
with XDL_HASHLONG()) for convenience.

Signed-off-by: Tay Ray Chuan <rctay89@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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commit 8c912eea94a2138e8bc608f7c390eb0b313effb0 1 parent 46c8f29
Tay Ray Chuan rctay authored gitster committed
2  Makefile
View
@@ -1838,7 +1838,7 @@ ifndef NO_CURL
GIT_OBJS += http.o http-walker.o remote-curl.o
endif
XDIFF_OBJS = xdiff/xdiffi.o xdiff/xprepare.o xdiff/xutils.o xdiff/xemit.o \
- xdiff/xmerge.o xdiff/xpatience.o
+ xdiff/xmerge.o xdiff/xpatience.o xdiff/xhistogram.o
VCSSVN_OBJS = vcs-svn/string_pool.o vcs-svn/line_buffer.o \
vcs-svn/repo_tree.o vcs-svn/fast_export.o vcs-svn/svndump.o
VCSSVN_TEST_OBJS = test-obj-pool.o test-string-pool.o \
2  diff.c
View
@@ -3369,6 +3369,8 @@ int diff_opt_parse(struct diff_options *options, const char **av, int ac)
DIFF_XDL_SET(options, IGNORE_WHITESPACE_AT_EOL);
else if (!strcmp(arg, "--patience"))
DIFF_XDL_SET(options, PATIENCE_DIFF);
+ else if (!strcmp(arg, "--histogram"))
+ DIFF_XDL_SET(options, HISTOGRAM_DIFF);
/* flags options */
else if (!strcmp(arg, "--binary")) {
2  merge-recursive.c
View
@@ -1759,6 +1759,8 @@ int parse_merge_opt(struct merge_options *o, const char *s)
o->subtree_shift = s + strlen("subtree=");
else if (!strcmp(s, "patience"))
o->xdl_opts |= XDF_PATIENCE_DIFF;
+ else if (!strcmp(s, "histogram"))
+ o->xdl_opts |= XDF_HISTOGRAM_DIFF;
else if (!strcmp(s, "ignore-space-change"))
o->xdl_opts |= XDF_IGNORE_WHITESPACE_CHANGE;
else if (!strcmp(s, "ignore-all-space"))
12 t/t4049-diff-histogram.sh
View
@@ -0,0 +1,12 @@
+#!/bin/sh
+
+test_description='histogram diff algorithm'
+
+. ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-diff-alternative.sh
+
+test_diff_frobnitz "histogram"
+
+test_diff_unique "histogram"
+
+test_done
1  xdiff/xdiff.h
View
@@ -33,6 +33,7 @@ extern "C" {
#define XDF_IGNORE_WHITESPACE_CHANGE (1 << 3)
#define XDF_IGNORE_WHITESPACE_AT_EOL (1 << 4)
#define XDF_PATIENCE_DIFF (1 << 5)
+#define XDF_HISTOGRAM_DIFF (1 << 6)
#define XDF_WHITESPACE_FLAGS (XDF_IGNORE_WHITESPACE | XDF_IGNORE_WHITESPACE_CHANGE | XDF_IGNORE_WHITESPACE_AT_EOL)
#define XDL_PATCH_NORMAL '-'
3  xdiff/xdiffi.c
View
@@ -331,6 +331,9 @@ int xdl_do_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
if (xpp->flags & XDF_PATIENCE_DIFF)
return xdl_do_patience_diff(mf1, mf2, xpp, xe);
+ if (xpp->flags & XDF_HISTOGRAM_DIFF)
+ return xdl_do_histogram_diff(mf1, mf2, xpp, xe);
+
if (xdl_prepare_env(mf1, mf2, xpp, xe) < 0) {
return -1;
2  xdiff/xdiffi.h
View
@@ -57,5 +57,7 @@ int xdl_emit_diff(xdfenv_t *xe, xdchange_t *xscr, xdemitcb_t *ecb,
xdemitconf_t const *xecfg);
int xdl_do_patience_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
xdfenv_t *env);
+int xdl_do_histogram_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
+ xdfenv_t *env);
#endif /* #if !defined(XDIFFI_H) */
384 xdiff/xhistogram.c
View
@@ -0,0 +1,384 @@
+/*
+ * Copyright (C) 2010, Google Inc.
+ * and other copyright owners as documented in JGit's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following
+ * disclaimer in the documentation and/or other materials provided
+ * with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ * names of its contributors may be used to endorse or promote
+ * products derived from this software without specific prior
+ * written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "xinclude.h"
+#include "xtypes.h"
+#include "xdiff.h"
+
+#define MAX_PTR UINT_MAX
+#define MAX_CNT UINT_MAX
+
+#define LINE_END(n) (line##n + count##n - 1)
+#define LINE_END_PTR(n) (*line##n + *count##n - 1)
+
+struct histindex {
+ struct record {
+ unsigned int ptr, cnt;
+ struct record *next;
+ } **records, /* an ocurrence */
+ **line_map; /* map of line to record chain */
+ chastore_t rcha;
+ unsigned int *next_ptrs;
+ unsigned int table_bits,
+ records_size,
+ line_map_size;
+
+ unsigned int max_chain_length,
+ key_shift,
+ ptr_shift;
+
+ unsigned int cnt,
+ has_common;
+
+ xdfenv_t *env;
+ xpparam_t const *xpp;
+};
+
+struct region {
+ unsigned int begin1, end1;
+ unsigned int begin2, end2;
+};
+
+#define LINE_MAP(i, a) (i->line_map[(a) - i->ptr_shift])
+
+#define NEXT_PTR(index, ptr) \
+ (index->next_ptrs[(ptr) - index->ptr_shift])
+
+#define CNT(index, ptr) \
+ ((LINE_MAP(index, ptr))->cnt)
+
+#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)
+{
+ return r1->ha == r2->ha &&
+ xdl_recmatch(r1->ptr, r1->size, r2->ptr, r2->size,
+ xpp->flags);
+}
+
+#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_ENV(i->xpp, i->env, s1, l1, 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, int line1, int count1)
+{
+ unsigned int ptr, tbl_idx;
+ unsigned int chain_len;
+ struct record **rec_chain, *rec;
+
+ for (ptr = LINE_END(1); line1 <= ptr; ptr--) {
+ tbl_idx = TABLE_HASH(index, 1, ptr);
+ rec_chain = index->records + tbl_idx;
+ rec = *rec_chain;
+
+ chain_len = 0;
+ while (rec) {
+ if (CMP(index, 1, rec->ptr, 1, ptr)) {
+ /*
+ * ptr is identical to another element. Insert
+ * it onto the front of the existing element
+ * chain.
+ */
+ NEXT_PTR(index, ptr) = rec->ptr;
+ rec->ptr = ptr;
+ /* cap rec->cnt at MAX_CNT */
+ rec->cnt = XDL_MIN(MAX_CNT, rec->cnt + 1);
+ LINE_MAP(index, ptr) = rec;
+ goto continue_scan;
+ }
+
+ rec = rec->next;
+ chain_len++;
+ }
+
+ if (chain_len == index->max_chain_length)
+ return -1;
+
+ /*
+ * This is the first time we have ever seen this particular
+ * element in the sequence. Construct a new chain for it.
+ */
+ if (!(rec = xdl_cha_alloc(&index->rcha)))
+ return -1;
+ rec->ptr = ptr;
+ rec->cnt = 1;
+ rec->next = *rec_chain;
+ *rec_chain = rec;
+ LINE_MAP(index, ptr) = rec;
+
+continue_scan:
+ ; /* no op */
+ }
+
+ return 0;
+}
+
+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)];
+ unsigned int as, ae, bs, be, np, rc;
+ int should_break;
+
+ for (; rec; rec = rec->next) {
+ if (rec->cnt > index->cnt) {
+ if (!index->has_common)
+ index->has_common = CMP(index, 1, rec->ptr, 2, b_ptr);
+ continue;
+ }
+
+ as = rec->ptr;
+ if (!CMP(index, 1, as, 2, b_ptr))
+ continue;
+
+ index->has_common = 1;
+ for (;;) {
+ should_break = 0;
+ np = NEXT_PTR(index, as);
+ bs = b_ptr;
+ ae = as;
+ be = bs;
+ rc = rec->cnt;
+
+ while (line1 < as && line2 < bs
+ && CMP(index, 1, as - 1, 2, bs - 1)) {
+ as--;
+ bs--;
+ if (1 < rc)
+ rc = XDL_MIN(rc, CNT(index, as));
+ }
+ while (ae < LINE_END(1) && be < LINE_END(2)
+ && CMP(index, 1, ae + 1, 2, be + 1)) {
+ ae++;
+ be++;
+ if (1 < rc)
+ rc = XDL_MIN(rc, CNT(index, ae));
+ }
+
+ if (b_next <= be)
+ b_next = be + 1;
+ if (lcs->end1 - lcs->begin1 < ae - as || rc < index->cnt) {
+ lcs->begin1 = as;
+ lcs->begin2 = bs;
+ lcs->end1 = ae;
+ lcs->end2 = be;
+ index->cnt = rc;
+ }
+
+ if (np == 0)
+ break;
+
+ while (np <= ae) {
+ np = NEXT_PTR(index, np);
+ if (np == 0) {
+ should_break = 1;
+ break;
+ }
+ }
+
+ if (should_break)
+ break;
+
+ as = np;
+ }
+ }
+ return b_next;
+}
+
+static int find_lcs(struct histindex *index, struct region *lcs,
+ int line1, int count1, int line2, int count2) {
+ int b_ptr;
+
+ if (scanA(index, line1, count1))
+ return -1;
+
+ 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);
+
+ return index->has_common && index->max_chain_length < index->cnt;
+}
+
+static void reduce_common_start_end(xpparam_t const *xpp, xdfenv_t *env,
+ int *line1, int *count1, int *line2, int *count2)
+{
+ if (*count1 <= 1 || *count2 <= 1)
+ return;
+ while (*count1 > 1 && *count2 > 1 && CMP_ENV(xpp, env, 1, *line1, 2, *line2)) {
+ (*line1)++;
+ (*count1)--;
+ (*line2)++;
+ (*count2)--;
+ }
+ while (*count1 > 1 && *count2 > 1 && CMP_ENV(xpp, env, 1, LINE_END_PTR(1), 2, LINE_END_PTR(2))) {
+ (*count1)--;
+ (*count2)--;
+ }
+}
+
+static int fall_back_to_classic_diff(struct histindex *index,
+ int line1, int count1, int line2, int count2)
+{
+ xpparam_t xpp;
+ xpp.flags = index->xpp->flags & ~XDF_HISTOGRAM_DIFF;
+
+ return xdl_fall_back_diff(index->env, &xpp,
+ line1, count1, line2, count2);
+}
+
+static int histogram_diff(xpparam_t const *xpp, xdfenv_t *env,
+ int line1, int count1, int line2, int count2)
+{
+ struct histindex index;
+ struct region lcs;
+ int 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));
+
+ index.env = env;
+ index.xpp = xpp;
+
+ index.records = NULL;
+ index.line_map = NULL;
+ /* in case of early xdl_cha_free() */
+ index.rcha.head = NULL;
+
+ index.table_bits = xdl_hashbits(count1);
+ sz = index.records_size = 1 << index.table_bits;
+ sz *= sizeof(struct record *);
+ if (!(index.records = (struct record **) xdl_malloc(sz)))
+ goto cleanup;
+ memset(index.records, 0, sz);
+
+ sz = index.line_map_size = count1;
+ sz *= sizeof(struct record *);
+ if (!(index.line_map = (struct record **) xdl_malloc(sz)))
+ goto cleanup;
+ memset(index.line_map, 0, sz);
+
+ sz = index.line_map_size;
+ sz *= sizeof(unsigned int);
+ if (!(index.next_ptrs = (unsigned int *) xdl_malloc(sz)))
+ goto cleanup;
+ memset(index.next_ptrs, 0, sz);
+
+ /* lines / 4 + 1 comes from xprepare.c:xdl_prepare_ctx() */
+ if (xdl_cha_init(&index.rcha, sizeof(struct record), count1 / 4 + 1) < 0)
+ goto cleanup;
+
+ index.ptr_shift = line1;
+ index.max_chain_length = 64;
+
+ 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);
+ else {
+ result = 0;
+ if (lcs.begin1 == 0 && lcs.begin2 == 0) {
+ int ptr;
+ for (ptr = 0; ptr < count1; ptr++)
+ env->xdf1.rchg[line1 + ptr - 1] = 1;
+ for (ptr = 0; ptr < count2; ptr++)
+ env->xdf2.rchg[line2 + ptr - 1] = 1;
+ } else {
+ result = histogram_diff(xpp, env,
+ line1, lcs.begin1 - line1,
+ line2, lcs.begin2 - line2);
+ result = histogram_diff(xpp, env,
+ lcs.end1 + 1, LINE_END(1) - lcs.end1,
+ lcs.end2 + 1, LINE_END(2) - lcs.end2);
+ result *= -1;
+ }
+ }
+
+cleanup:
+ xdl_free(index.records);
+ xdl_free(index.line_map);
+ xdl_free(index.next_ptrs);
+ xdl_cha_free(&index.rcha);
+
+ return result;
+}
+
+int xdl_do_histogram_diff(mmfile_t *file1, mmfile_t *file2,
+ xpparam_t const *xpp, xdfenv_t *env)
+{
+ int line1, line2, count1, count2;
+
+ if (xdl_prepare_env(file1, file2, xpp, env) < 0)
+ return -1;
+
+ line1 = line2 = 1;
+ count1 = env->xdf1.nrec;
+ count2 = env->xdf2.nrec;
+
+ reduce_common_start_end(xpp, env, &line1, &count1, &line2, &count2);
+
+ return histogram_diff(xpp, env, line1, count1, line2, count2);
+}
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