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-rw-r--r--diff-delta.c286
1 files changed, 286 insertions, 0 deletions
diff --git a/diff-delta.c b/diff-delta.c
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+++ b/diff-delta.c
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+/*
+ * 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 <zlib.h>
+#include "delta.h"
+
+
+/* block size: min = 16, max = 64k, power of 2 */
+#define BLK_SIZE 16
+
+#define MIN(a, b) ((a) < (b) ? (a) : (b))
+
+#define GR_PRIME 0x9e370001
+#define HASH(v, shift) (((unsigned int)(v) * GR_PRIME) >> (shift))
+
+struct index {
+ const unsigned char *ptr;
+ unsigned int val;
+ struct index *next;
+};
+
+static struct index ** delta_index(const unsigned char *buf,
+ unsigned long bufsize,
+ unsigned long trg_bufsize,
+ unsigned int *hash_shift)
+{
+ unsigned int i, hsize, hshift, hlimit, entries, *hash_count;
+ const unsigned char *data;
+ struct index *entry, **hash;
+ void *mem;
+
+ /* determine index hash size */
+ entries = bufsize / BLK_SIZE;
+ hsize = entries / 4;
+ for (i = 4; (1 << i) < hsize && i < 31; i++);
+ hsize = 1 << i;
+ hshift = 32 - i;
+ *hash_shift = hshift;
+
+ /* allocate lookup index */
+ mem = malloc(hsize * sizeof(*hash) + entries * sizeof(*entry));
+ if (!mem)
+ return NULL;
+ hash = mem;
+ entry = mem + hsize * sizeof(*hash);
+ memset(hash, 0, hsize * sizeof(*hash));
+
+ /* allocate an array to count hash entries */
+ hash_count = calloc(hsize, sizeof(*hash_count));
+ if (!hash_count) {
+ free(hash);
+ return NULL;
+ }
+
+ /* then populate the index */
+ data = buf + entries * BLK_SIZE - BLK_SIZE;
+ while (data >= buf) {
+ unsigned int val = adler32(0, data, BLK_SIZE);
+ i = HASH(val, hshift);
+ entry->ptr = data;
+ entry->val = val;
+ entry->next = hash[i];
+ hash[i] = entry++;
+ hash_count[i]++;
+ data -= BLK_SIZE;
+ }
+
+ /*
+ * 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).
+ *
+ * The more the target buffer is large, the more it is important to
+ * have small entry lists for each hash buckets. With such a limit
+ * the cost is bounded to something more like O(m+n).
+ */
+ hlimit = (1 << 26) / trg_bufsize;
+ if (hlimit < 4*BLK_SIZE)
+ hlimit = 4*BLK_SIZE;
+
+ /*
+ * Now 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] < hlimit)
+ continue;
+ entry = hash[i];
+ do {
+ struct index *keep = entry;
+ int skip = hash_count[i] / hlimit / 2;
+ do {
+ entry = entry->next;
+ } while(--skip && entry);
+ keep->next = entry;
+ } while(entry);
+ }
+ free(hash_count);
+
+ return hash;
+}
+
+/* provide the size of the copy opcode given the block offset and size */
+#define COPYOP_SIZE(o, s) \
+ (!!(o & 0xff) + !!(o & 0xff00) + !!(o & 0xff0000) + !!(o & 0xff000000) + \
+ !!(s & 0xff) + !!(s & 0xff00) + 1)
+
+/* the maximum size for any opcode */
+#define MAX_OP_SIZE COPYOP_SIZE(0xffffffff, 0xffffffff)
+
+void *diff_delta(void *from_buf, unsigned long from_size,
+ void *to_buf, unsigned long to_size,
+ unsigned long *delta_size,
+ unsigned long max_size)
+{
+ unsigned int i, outpos, outsize, hash_shift;
+ int inscnt;
+ const unsigned char *ref_data, *ref_top, *data, *top;
+ unsigned char *out;
+ struct index *entry, **hash;
+
+ if (!from_size || !to_size)
+ return NULL;
+ hash = delta_index(from_buf, from_size, to_size, &hash_shift);
+ if (!hash)
+ return NULL;
+
+ outpos = 0;
+ outsize = 8192;
+ if (max_size && outsize >= max_size)
+ outsize = max_size + MAX_OP_SIZE + 1;
+ out = malloc(outsize);
+ if (!out) {
+ free(hash);
+ return NULL;
+ }
+
+ ref_data = from_buf;
+ ref_top = from_buf + from_size;
+ data = to_buf;
+ top = to_buf + to_size;
+
+ /* store reference buffer size */
+ out[outpos++] = from_size;
+ from_size >>= 7;
+ while (from_size) {
+ out[outpos - 1] |= 0x80;
+ out[outpos++] = from_size;
+ from_size >>= 7;
+ }
+
+ /* store target buffer size */
+ out[outpos++] = to_size;
+ to_size >>= 7;
+ while (to_size) {
+ out[outpos - 1] |= 0x80;
+ out[outpos++] = to_size;
+ to_size >>= 7;
+ }
+
+ inscnt = 0;
+
+ while (data < top) {
+ unsigned int moff = 0, msize = 0;
+ if (data + BLK_SIZE <= top) {
+ unsigned int val = adler32(0, data, BLK_SIZE);
+ i = HASH(val, hash_shift);
+ for (entry = 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 || msize < COPYOP_SIZE(moff, msize)) {
+ if (!inscnt)
+ outpos++;
+ out[outpos++] = *data++;
+ inscnt++;
+ if (inscnt == 0x7f) {
+ out[outpos - inscnt - 1] = inscnt;
+ inscnt = 0;
+ }
+ } else {
+ unsigned char *op;
+
+ 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)
+ out = NULL;
+ else
+ out = realloc(out, outsize);
+ if (!out) {
+ free(tmp);
+ free(hash);
+ return NULL;
+ }
+ }
+ }
+
+ if (inscnt)
+ out[outpos - inscnt - 1] = inscnt;
+
+ free(hash);
+ *delta_size = outpos;
+ return out;
+}
generated by cgit v1.2.3 (git 2.25.1) at 2025-01-01 01:24:17 +0000