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git/diff-delta.c
Nicolas Pitre 06a9f92035 improve diff-delta with sparse and/or repetitive data
It is useless to preserve multiple hash entries for consecutive blocks
with the same hash.  Keeping only the first one will allow for matching
the longest string of identical bytes while subsequent blocks will only
allow for shorter matches.  The backward matching code will match the
end of it as necessary.

This improves both performances (no repeated string compare with long
successions of identical bytes, or even small group of bytes), as well
as compression (less likely to need random hash bucket entry culling),
especially with sparse files.

With well behaved data sets this patch doesn't change much.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
2006-05-02 21:32:39 -07:00

417 lines
14 KiB
C

/*
* diff-delta.c: generate a delta between two buffers
*
* Many parts of this file have been lifted from LibXDiff version 0.10.
* http://www.xmailserver.org/xdiff-lib.html
*
* LibXDiff was written by Davide Libenzi <davidel@xmailserver.org>
* Copyright (C) 2003 Davide Libenzi
*
* Many mods for GIT usage by Nicolas Pitre <nico@cam.org>, (C) 2005.
*
* This file is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* Use of this within git automatically means that the LGPL
* licensing gets turned into GPLv2 within this project.
*/
#include <stdlib.h>
#include <string.h>
#include "delta.h"
/* maximum hash entry list for the same hash bucket */
#define HASH_LIMIT 64
#define RABIN_SHIFT 23
#define RABIN_WINDOW 16
static const unsigned int T[256] = {
0x00000000, 0xab59b4d1, 0x56b369a2, 0xfdeadd73, 0x063f6795, 0xad66d344,
0x508c0e37, 0xfbd5bae6, 0x0c7ecf2a, 0xa7277bfb, 0x5acda688, 0xf1941259,
0x0a41a8bf, 0xa1181c6e, 0x5cf2c11d, 0xf7ab75cc, 0x18fd9e54, 0xb3a42a85,
0x4e4ef7f6, 0xe5174327, 0x1ec2f9c1, 0xb59b4d10, 0x48719063, 0xe32824b2,
0x1483517e, 0xbfdae5af, 0x423038dc, 0xe9698c0d, 0x12bc36eb, 0xb9e5823a,
0x440f5f49, 0xef56eb98, 0x31fb3ca8, 0x9aa28879, 0x6748550a, 0xcc11e1db,
0x37c45b3d, 0x9c9defec, 0x6177329f, 0xca2e864e, 0x3d85f382, 0x96dc4753,
0x6b369a20, 0xc06f2ef1, 0x3bba9417, 0x90e320c6, 0x6d09fdb5, 0xc6504964,
0x2906a2fc, 0x825f162d, 0x7fb5cb5e, 0xd4ec7f8f, 0x2f39c569, 0x846071b8,
0x798aaccb, 0xd2d3181a, 0x25786dd6, 0x8e21d907, 0x73cb0474, 0xd892b0a5,
0x23470a43, 0x881ebe92, 0x75f463e1, 0xdeadd730, 0x63f67950, 0xc8afcd81,
0x354510f2, 0x9e1ca423, 0x65c91ec5, 0xce90aa14, 0x337a7767, 0x9823c3b6,
0x6f88b67a, 0xc4d102ab, 0x393bdfd8, 0x92626b09, 0x69b7d1ef, 0xc2ee653e,
0x3f04b84d, 0x945d0c9c, 0x7b0be704, 0xd05253d5, 0x2db88ea6, 0x86e13a77,
0x7d348091, 0xd66d3440, 0x2b87e933, 0x80de5de2, 0x7775282e, 0xdc2c9cff,
0x21c6418c, 0x8a9ff55d, 0x714a4fbb, 0xda13fb6a, 0x27f92619, 0x8ca092c8,
0x520d45f8, 0xf954f129, 0x04be2c5a, 0xafe7988b, 0x5432226d, 0xff6b96bc,
0x02814bcf, 0xa9d8ff1e, 0x5e738ad2, 0xf52a3e03, 0x08c0e370, 0xa39957a1,
0x584ced47, 0xf3155996, 0x0eff84e5, 0xa5a63034, 0x4af0dbac, 0xe1a96f7d,
0x1c43b20e, 0xb71a06df, 0x4ccfbc39, 0xe79608e8, 0x1a7cd59b, 0xb125614a,
0x468e1486, 0xedd7a057, 0x103d7d24, 0xbb64c9f5, 0x40b17313, 0xebe8c7c2,
0x16021ab1, 0xbd5bae60, 0x6cb54671, 0xc7ecf2a0, 0x3a062fd3, 0x915f9b02,
0x6a8a21e4, 0xc1d39535, 0x3c394846, 0x9760fc97, 0x60cb895b, 0xcb923d8a,
0x3678e0f9, 0x9d215428, 0x66f4eece, 0xcdad5a1f, 0x3047876c, 0x9b1e33bd,
0x7448d825, 0xdf116cf4, 0x22fbb187, 0x89a20556, 0x7277bfb0, 0xd92e0b61,
0x24c4d612, 0x8f9d62c3, 0x7836170f, 0xd36fa3de, 0x2e857ead, 0x85dcca7c,
0x7e09709a, 0xd550c44b, 0x28ba1938, 0x83e3ade9, 0x5d4e7ad9, 0xf617ce08,
0x0bfd137b, 0xa0a4a7aa, 0x5b711d4c, 0xf028a99d, 0x0dc274ee, 0xa69bc03f,
0x5130b5f3, 0xfa690122, 0x0783dc51, 0xacda6880, 0x570fd266, 0xfc5666b7,
0x01bcbbc4, 0xaae50f15, 0x45b3e48d, 0xeeea505c, 0x13008d2f, 0xb85939fe,
0x438c8318, 0xe8d537c9, 0x153feaba, 0xbe665e6b, 0x49cd2ba7, 0xe2949f76,
0x1f7e4205, 0xb427f6d4, 0x4ff24c32, 0xe4abf8e3, 0x19412590, 0xb2189141,
0x0f433f21, 0xa41a8bf0, 0x59f05683, 0xf2a9e252, 0x097c58b4, 0xa225ec65,
0x5fcf3116, 0xf49685c7, 0x033df00b, 0xa86444da, 0x558e99a9, 0xfed72d78,
0x0502979e, 0xae5b234f, 0x53b1fe3c, 0xf8e84aed, 0x17bea175, 0xbce715a4,
0x410dc8d7, 0xea547c06, 0x1181c6e0, 0xbad87231, 0x4732af42, 0xec6b1b93,
0x1bc06e5f, 0xb099da8e, 0x4d7307fd, 0xe62ab32c, 0x1dff09ca, 0xb6a6bd1b,
0x4b4c6068, 0xe015d4b9, 0x3eb80389, 0x95e1b758, 0x680b6a2b, 0xc352defa,
0x3887641c, 0x93ded0cd, 0x6e340dbe, 0xc56db96f, 0x32c6cca3, 0x999f7872,
0x6475a501, 0xcf2c11d0, 0x34f9ab36, 0x9fa01fe7, 0x624ac294, 0xc9137645,
0x26459ddd, 0x8d1c290c, 0x70f6f47f, 0xdbaf40ae, 0x207afa48, 0x8b234e99,
0x76c993ea, 0xdd90273b, 0x2a3b52f7, 0x8162e626, 0x7c883b55, 0xd7d18f84,
0x2c043562, 0x875d81b3, 0x7ab75cc0, 0xd1eee811
};
static const unsigned int U[256] = {
0x00000000, 0x7eb5200d, 0x5633f4cb, 0x2886d4c6, 0x073e5d47, 0x798b7d4a,
0x510da98c, 0x2fb88981, 0x0e7cba8e, 0x70c99a83, 0x584f4e45, 0x26fa6e48,
0x0942e7c9, 0x77f7c7c4, 0x5f711302, 0x21c4330f, 0x1cf9751c, 0x624c5511,
0x4aca81d7, 0x347fa1da, 0x1bc7285b, 0x65720856, 0x4df4dc90, 0x3341fc9d,
0x1285cf92, 0x6c30ef9f, 0x44b63b59, 0x3a031b54, 0x15bb92d5, 0x6b0eb2d8,
0x4388661e, 0x3d3d4613, 0x39f2ea38, 0x4747ca35, 0x6fc11ef3, 0x11743efe,
0x3eccb77f, 0x40799772, 0x68ff43b4, 0x164a63b9, 0x378e50b6, 0x493b70bb,
0x61bda47d, 0x1f088470, 0x30b00df1, 0x4e052dfc, 0x6683f93a, 0x1836d937,
0x250b9f24, 0x5bbebf29, 0x73386bef, 0x0d8d4be2, 0x2235c263, 0x5c80e26e,
0x740636a8, 0x0ab316a5, 0x2b7725aa, 0x55c205a7, 0x7d44d161, 0x03f1f16c,
0x2c4978ed, 0x52fc58e0, 0x7a7a8c26, 0x04cfac2b, 0x73e5d470, 0x0d50f47d,
0x25d620bb, 0x5b6300b6, 0x74db8937, 0x0a6ea93a, 0x22e87dfc, 0x5c5d5df1,
0x7d996efe, 0x032c4ef3, 0x2baa9a35, 0x551fba38, 0x7aa733b9, 0x041213b4,
0x2c94c772, 0x5221e77f, 0x6f1ca16c, 0x11a98161, 0x392f55a7, 0x479a75aa,
0x6822fc2b, 0x1697dc26, 0x3e1108e0, 0x40a428ed, 0x61601be2, 0x1fd53bef,
0x3753ef29, 0x49e6cf24, 0x665e46a5, 0x18eb66a8, 0x306db26e, 0x4ed89263,
0x4a173e48, 0x34a21e45, 0x1c24ca83, 0x6291ea8e, 0x4d29630f, 0x339c4302,
0x1b1a97c4, 0x65afb7c9, 0x446b84c6, 0x3adea4cb, 0x1258700d, 0x6ced5000,
0x4355d981, 0x3de0f98c, 0x15662d4a, 0x6bd30d47, 0x56ee4b54, 0x285b6b59,
0x00ddbf9f, 0x7e689f92, 0x51d01613, 0x2f65361e, 0x07e3e2d8, 0x7956c2d5,
0x5892f1da, 0x2627d1d7, 0x0ea10511, 0x7014251c, 0x5facac9d, 0x21198c90,
0x099f5856, 0x772a785b, 0x4c921c31, 0x32273c3c, 0x1aa1e8fa, 0x6414c8f7,
0x4bac4176, 0x3519617b, 0x1d9fb5bd, 0x632a95b0, 0x42eea6bf, 0x3c5b86b2,
0x14dd5274, 0x6a687279, 0x45d0fbf8, 0x3b65dbf5, 0x13e30f33, 0x6d562f3e,
0x506b692d, 0x2ede4920, 0x06589de6, 0x78edbdeb, 0x5755346a, 0x29e01467,
0x0166c0a1, 0x7fd3e0ac, 0x5e17d3a3, 0x20a2f3ae, 0x08242768, 0x76910765,
0x59298ee4, 0x279caee9, 0x0f1a7a2f, 0x71af5a22, 0x7560f609, 0x0bd5d604,
0x235302c2, 0x5de622cf, 0x725eab4e, 0x0ceb8b43, 0x246d5f85, 0x5ad87f88,
0x7b1c4c87, 0x05a96c8a, 0x2d2fb84c, 0x539a9841, 0x7c2211c0, 0x029731cd,
0x2a11e50b, 0x54a4c506, 0x69998315, 0x172ca318, 0x3faa77de, 0x411f57d3,
0x6ea7de52, 0x1012fe5f, 0x38942a99, 0x46210a94, 0x67e5399b, 0x19501996,
0x31d6cd50, 0x4f63ed5d, 0x60db64dc, 0x1e6e44d1, 0x36e89017, 0x485db01a,
0x3f77c841, 0x41c2e84c, 0x69443c8a, 0x17f11c87, 0x38499506, 0x46fcb50b,
0x6e7a61cd, 0x10cf41c0, 0x310b72cf, 0x4fbe52c2, 0x67388604, 0x198da609,
0x36352f88, 0x48800f85, 0x6006db43, 0x1eb3fb4e, 0x238ebd5d, 0x5d3b9d50,
0x75bd4996, 0x0b08699b, 0x24b0e01a, 0x5a05c017, 0x728314d1, 0x0c3634dc,
0x2df207d3, 0x534727de, 0x7bc1f318, 0x0574d315, 0x2acc5a94, 0x54797a99,
0x7cffae5f, 0x024a8e52, 0x06852279, 0x78300274, 0x50b6d6b2, 0x2e03f6bf,
0x01bb7f3e, 0x7f0e5f33, 0x57888bf5, 0x293dabf8, 0x08f998f7, 0x764cb8fa,
0x5eca6c3c, 0x207f4c31, 0x0fc7c5b0, 0x7172e5bd, 0x59f4317b, 0x27411176,
0x1a7c5765, 0x64c97768, 0x4c4fa3ae, 0x32fa83a3, 0x1d420a22, 0x63f72a2f,
0x4b71fee9, 0x35c4dee4, 0x1400edeb, 0x6ab5cde6, 0x42331920, 0x3c86392d,
0x133eb0ac, 0x6d8b90a1, 0x450d4467, 0x3bb8646a
};
struct index_entry {
const unsigned char *ptr;
unsigned int val;
struct index_entry *next;
};
struct delta_index {
const void *src_buf;
unsigned long src_size;
unsigned int hash_mask;
struct index_entry *hash[0];
};
struct delta_index * create_delta_index(const void *buf, unsigned long bufsize)
{
unsigned int i, hsize, hmask, entries, prev_val, *hash_count;
const unsigned char *data, *buffer = buf;
struct delta_index *index;
struct index_entry *entry, **hash;
void *mem;
unsigned long memsize;
if (!buf || !bufsize)
return NULL;
/* Determine index hash size. Note that indexing skips the
first byte to allow for optimizing the rabin polynomial
initialization in create_delta(). */
entries = (bufsize - 1) / RABIN_WINDOW;
hsize = entries / 4;
for (i = 4; (1 << i) < hsize && i < 31; i++);
hsize = 1 << i;
hmask = hsize - 1;
/* allocate lookup index */
memsize = sizeof(*index) +
sizeof(*hash) * hsize +
sizeof(*entry) * entries;
mem = malloc(memsize);
if (!mem)
return NULL;
index = mem;
mem = index + 1;
hash = mem;
mem = hash + hsize;
entry = mem;
index->src_buf = buf;
index->src_size = bufsize;
index->hash_mask = hmask;
memset(hash, 0, hsize * sizeof(*hash));
/* allocate an array to count hash entries */
hash_count = calloc(hsize, sizeof(*hash_count));
if (!hash_count) {
free(index);
return NULL;
}
/* then populate the index */
prev_val = ~0;
for (data = buffer + entries * RABIN_WINDOW - RABIN_WINDOW;
data >= buffer;
data -= RABIN_WINDOW) {
unsigned int val = 0;
for (i = 1; i <= RABIN_WINDOW; i++)
val = ((val << 8) | data[i]) ^ T[val >> RABIN_SHIFT];
if (val == prev_val) {
/* keep the lowest of consecutive identical blocks */
entry[-1].ptr = data + RABIN_WINDOW;
} else {
prev_val = val;
i = val & hmask;
entry->ptr = data + RABIN_WINDOW;
entry->val = val;
entry->next = hash[i];
hash[i] = entry++;
hash_count[i]++;
entries--;
}
}
/*
* Determine a limit on the number of entries in the same hash
* bucket. This guard us against patological data sets causing
* really bad hash distribution with most entries in the same hash
* bucket that would bring us to O(m*n) computing costs (m and n
* corresponding to reference and target buffer sizes).
*
* Make sure none of the hash buckets has more entries than
* we're willing to test. Otherwise we cull the entry list
* uniformly to still preserve a good repartition across
* the reference buffer.
*/
for (i = 0; i < hsize; i++) {
if (hash_count[i] < HASH_LIMIT)
continue;
entry = hash[i];
do {
struct index_entry *keep = entry;
int skip = hash_count[i] / HASH_LIMIT / 2;
do {
entry = entry->next;
} while(--skip && entry);
keep->next = entry;
} while(entry);
}
free(hash_count);
/* If we didn't use all hash entries, free the unused memory. */
if (entries)
index = realloc(index, memsize - entries * sizeof(*entry));
return index;
}
void free_delta_index(struct delta_index *index)
{
free(index);
}
/*
* The maximum size for any opcode sequence, including the initial header
* plus rabin window plus biggest copy.
*/
#define MAX_OP_SIZE (5 + 5 + 1 + RABIN_WINDOW + 7)
void *
create_delta(const struct delta_index *index,
const void *trg_buf, unsigned long trg_size,
unsigned long *delta_size, unsigned long max_size)
{
unsigned int i, outpos, outsize, val;
int inscnt;
const unsigned char *ref_data, *ref_top, *data, *top;
unsigned char *out;
if (!trg_buf || !trg_size)
return NULL;
outpos = 0;
outsize = 8192;
if (max_size && outsize >= max_size)
outsize = max_size + MAX_OP_SIZE + 1;
out = malloc(outsize);
if (!out)
return NULL;
/* store reference buffer size */
i = index->src_size;
while (i >= 0x80) {
out[outpos++] = i | 0x80;
i >>= 7;
}
out[outpos++] = i;
/* store target buffer size */
i = trg_size;
while (i >= 0x80) {
out[outpos++] = i | 0x80;
i >>= 7;
}
out[outpos++] = i;
ref_data = index->src_buf;
ref_top = ref_data + index->src_size;
data = trg_buf;
top = trg_buf + trg_size;
outpos++;
val = 0;
for (i = 0; i < RABIN_WINDOW && data < top; i++, data++) {
out[outpos++] = *data;
val = ((val << 8) | *data) ^ T[val >> RABIN_SHIFT];
}
inscnt = i;
while (data < top) {
unsigned int moff = 0, msize = 0;
struct index_entry *entry;
val ^= U[data[-RABIN_WINDOW]];
val = ((val << 8) | *data) ^ T[val >> RABIN_SHIFT];
i = val & index->hash_mask;
for (entry = index->hash[i]; entry; entry = entry->next) {
const unsigned char *ref = entry->ptr;
const unsigned char *src = data;
unsigned int ref_size = ref_top - ref;
if (entry->val != val)
continue;
if (ref_size > top - src)
ref_size = top - src;
if (ref_size > 0x10000)
ref_size = 0x10000;
if (ref_size <= msize)
break;
while (ref_size-- && *src++ == *ref)
ref++;
if (msize < ref - entry->ptr) {
/* this is our best match so far */
msize = ref - entry->ptr;
moff = entry->ptr - ref_data;
}
}
if (msize < 4) {
if (!inscnt)
outpos++;
out[outpos++] = *data++;
inscnt++;
if (inscnt == 0x7f) {
out[outpos - inscnt - 1] = inscnt;
inscnt = 0;
}
} else {
unsigned char *op;
if (msize >= RABIN_WINDOW) {
const unsigned char *sk;
sk = data + msize - RABIN_WINDOW;
val = 0;
for (i = 0; i < RABIN_WINDOW; i++)
val = ((val << 8) | *sk++) ^ T[val >> RABIN_SHIFT];
} else {
const unsigned char *sk = data + 1;
for (i = 1; i < msize; i++) {
val ^= U[sk[-RABIN_WINDOW]];
val = ((val << 8) | *sk++) ^ T[val >> RABIN_SHIFT];
}
}
if (inscnt) {
while (moff && ref_data[moff-1] == data[-1]) {
if (msize == 0x10000)
break;
/* we can match one byte back */
msize++;
moff--;
data--;
outpos--;
if (--inscnt)
continue;
outpos--; /* remove count slot */
inscnt--; /* make it -1 */
break;
}
out[outpos - inscnt - 1] = inscnt;
inscnt = 0;
}
data += msize;
op = out + outpos++;
i = 0x80;
if (moff & 0xff) { out[outpos++] = moff; i |= 0x01; }
moff >>= 8;
if (moff & 0xff) { out[outpos++] = moff; i |= 0x02; }
moff >>= 8;
if (moff & 0xff) { out[outpos++] = moff; i |= 0x04; }
moff >>= 8;
if (moff & 0xff) { out[outpos++] = moff; i |= 0x08; }
if (msize & 0xff) { out[outpos++] = msize; i |= 0x10; }
msize >>= 8;
if (msize & 0xff) { out[outpos++] = msize; i |= 0x20; }
*op = i;
}
if (outpos >= outsize - MAX_OP_SIZE) {
void *tmp = out;
outsize = outsize * 3 / 2;
if (max_size && outsize >= max_size)
outsize = max_size + MAX_OP_SIZE + 1;
if (max_size && outpos > max_size)
break;
out = realloc(out, outsize);
if (!out) {
free(tmp);
return NULL;
}
}
}
if (inscnt)
out[outpos - inscnt - 1] = inscnt;
if (max_size && outpos > max_size) {
free(out);
return NULL;
}
*delta_size = outpos;
return out;
}