/*
* 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
+ * This code was greatly inspired by parts of LibXDiff from Davide Libenzi
+ * http://www.xmailserver.org/xdiff-lib.html
*
- * LibXDiff was written by Davide Libenzi <davidel@xmailserver.org>
- * Copyright (C) 2003 Davide Libenzi
+ * Rewritten for GIT by Nicolas Pitre <nico@cam.org>, (C) 2005-2007
*
- * 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.
+ * This code is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
*/
-#include <stdlib.h>
-#include <string.h>
+#include "git-compat-util.h"
#include "delta.h"
-
/* maximum hash entry list for the same hash bucket */
#define HASH_LIMIT 64
const void *src_buf;
unsigned long src_size;
unsigned int hash_mask;
- struct index_entry *hash[0];
+ struct index_entry *hash[FLEX_ARRAY];
};
struct delta_index * create_delta_index(const void *buf, unsigned long bufsize)
{
- unsigned int i, hsize, hmask, entries, *hash_count;
+ 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
+ first byte to allow for optimizing the Rabin's polynomial
initialization in create_delta(). */
entries = (bufsize - 1) / RABIN_WINDOW;
hsize = entries / 4;
- for (i = 4; (1 << i) < hsize && i < 31; i++);
+ for (i = 4; (1u << i) < hsize && i < 31; i++);
hsize = 1 << i;
hmask = hsize - 1;
/* allocate lookup index */
- mem = malloc(sizeof(*index) +
- sizeof(*hash) * hsize +
- sizeof(*entry) * entries);
+ memsize = sizeof(*index) +
+ sizeof(*hash) * hsize +
+ sizeof(*entry) * entries;
+ mem = malloc(memsize);
if (!mem)
return NULL;
index = mem;
}
/* then populate the index */
- data = buffer + entries * RABIN_WINDOW - RABIN_WINDOW;
- while (data >= buffer) {
+ 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];
- i = val & hmask;
- entry->ptr = data + RABIN_WINDOW;
- entry->val = val;
- entry->next = hash[i];
- hash[i] = entry++;
- hash_count[i]++;
- data -= RABIN_WINDOW;
+ 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]++;
+ }
}
/*
* Determine a limit on the number of entries in the same hash
- * bucket. This guard us against patological data sets causing
+ * bucket. This guards us against pathological 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).
/*
* The maximum size for any opcode sequence, including the initial header
- * plus rabin window plus biggest copy.
+ * plus Rabin window plus biggest copy.
*/
#define MAX_OP_SIZE (5 + 5 + 1 + RABIN_WINDOW + 7)
const void *trg_buf, unsigned long trg_size,
unsigned long *delta_size, unsigned long max_size)
{
- unsigned int i, outpos, outsize, hash_mask, val;
+ unsigned int i, outpos, outsize, moff, msize, val;
int inscnt;
const unsigned char *ref_data, *ref_top, *data, *top;
unsigned char *out;
ref_data = index->src_buf;
ref_top = ref_data + index->src_size;
data = trg_buf;
- top = trg_buf + trg_size;
- hash_mask = index->hash_mask;
+ top = (const unsigned char *) trg_buf + trg_size;
outpos++;
val = 0;
}
inscnt = i;
+ moff = 0;
+ msize = 0;
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 & 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 < 4096) {
+ 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 <= 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 >= 4096) /* good enough */
+ break;
+ }
}
}
out[outpos - inscnt - 1] = inscnt;
inscnt = 0;
}
+ msize = 0;
} else {
+ unsigned int left;
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--;
inscnt = 0;
}
- data += msize;
+ /* A copy op is currently limited to 64KB (pack v2) */
+ left = (msize < 0x10000) ? 0 : (msize - 0x10000);
+ msize -= left;
+
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 (moff & 0x000000ff)
+ out[outpos++] = moff >> 0, i |= 0x01;
+ if (moff & 0x0000ff00)
+ out[outpos++] = moff >> 8, i |= 0x02;
+ if (moff & 0x00ff0000)
+ out[outpos++] = moff >> 16, i |= 0x04;
+ if (moff & 0xff000000)
+ out[outpos++] = moff >> 24, i |= 0x08;
- if (msize & 0xff) { out[outpos++] = msize; i |= 0x10; }
- msize >>= 8;
- if (msize & 0xff) { out[outpos++] = msize; i |= 0x20; }
+ if (msize & 0x00ff)
+ out[outpos++] = msize >> 0, i |= 0x10;
+ if (msize & 0xff00)
+ out[outpos++] = msize >> 8, i |= 0x20;
*op = i;
+
+ data += msize;
+ moff += msize;
+ msize = left;
+
+ if (msize < 4096) {
+ int j;
+ val = 0;
+ for (j = -RABIN_WINDOW; j < 0; j++)
+ val = ((val << 8) | data[j])
+ ^ T[val >> RABIN_SHIFT];
+ }
}
if (outpos >= outsize - MAX_OP_SIZE) {