This patch splits the diff-delta interface into index creation and delta
generation. A wrapper is provided to preserve the diff-delta() call.
This will allow for an optimization in pack-objects.c where the source
object could be fixed and a full window of objects tentatively tried
against
that same source object without recomputing the source index each time.
This patch only restructure things, plus a couple cleanups for good
measure. There is no performance change yet.
Signed-off-by: Nicolas Pitre <nico@xxxxxxx>
---
diff --git a/delta.h b/delta.h
index 9464f3e..9ef44c1 100644
--- a/delta.h
+++ b/delta.h
@@ -1,12 +1,73 @@
#ifndef DELTA_H
#define DELTA_H
-/* handling of delta buffers */
-extern 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);
-extern void *patch_delta(void *src_buf, unsigned long src_size,
- void *delta_buf, unsigned long delta_size,
+/* opaque object for delta index */
+struct delta_index;
+
+/*
+ * create_delta_index: compute index data from given buffer
+ *
+ * This returns a pointer to a struct delta_index that should be passed to
+ * subsequent create_delta() calls, or to free_delta_index(). A NULL pointer
+ * is returned on failure. The given buffer must not be freed nor altered
+ * before free_delta_index() is called. The returned pointer must be freed
+ * using free_delta_index().
+ */
+extern struct delta_index *
+create_delta_index(const void *buf, unsigned long bufsize);
+
+/*
+ * free_delta_index: free the index created by create_delta_index()
+ */
+extern void free_delta_index(struct delta_index *index);
+
+/*
+ * create_delta: create a delta from given index for the given buffer
+ *
+ * This function may be called multiple times with different buffers using
+ * the same delta_index pointer. If max_delta_size is non-zero and the
+ * resulting delta is to be larger than max_delta_size then NULL is returned.
+ * On success, a non-NULL pointer to the buffer with the delta data is
+ * returned and *delta_size is updated with its size. The returned buffer
+ * must be freed by the caller.
+ */
+extern void *
+create_delta(const struct delta_index *index,
+ const void *buf, unsigned long bufsize,
+ unsigned long *delta_size, unsigned long max_delta_size);
+
+/*
+ * diff_delta: create a delta from source buffer to target buffer
+ *
+ * If max_delta_size is non-zero and the resulting delta is to be larger
+ * than max_delta_size then NULL is returned. On success, a non-NULL
+ * pointer to the buffer with the delta data is returned and *delta_size is
+ * updated with its size. The returned buffer must be freed by the caller.
+ */
+static inline void *
+diff_delta(const void *src_buf, unsigned long src_bufsize,
+ const void *trg_buf, unsigned long trg_bufsize,
+ unsigned long *delta_size, unsigned long max_delta_size)
+{
+ struct delta_index *index = create_delta_index(src_buf, src_bufsize);
+ if (index) {
+ void *delta = create_delta(index, trg_buf, trg_bufsize,
+ delta_size, max_delta_size);
+ free_delta_index(index);
+ return delta;
+ }
+ return NULL;
+}
+
+/*
+ * patch_delta: recreate target buffer given source buffer and delta data
+ *
+ * On success, a non-NULL pointer to the target buffer is returned and
+ * *trg_bufsize is updated with its size. On failure a NULL pointer is
+ * returned. The returned buffer must be freed by the caller.
+ */
+extern void *patch_delta(const void *src_buf, unsigned long src_size,
+ const void *delta_buf, unsigned long delta_size,
unsigned long *dst_size);
/* the smallest possible delta size is 4 bytes */
@@ -14,7 +75,7 @@ #define DELTA_SIZE_MIN 4
/*
* This must be called twice on the delta data buffer, first to get the
- * expected reference buffer size, and again to get the result buffer size.
+ * expected source buffer size, and again to get the target buffer size.
*/
static inline unsigned long get_delta_hdr_size(const unsigned char **datap,
const unsigned char *top)
diff --git a/diff-delta.c b/diff-delta.c
index 1188b31..fdedf94 100644
--- a/diff-delta.c
+++ b/diff-delta.c
@@ -27,53 +27,70 @@ #include "delta.h"
/* block size: min = 16, max = 64k, power of 2 */
#define BLK_SIZE 16
-#define MIN(a, b) ((a) < (b) ? (a) : (b))
+/* maximum hash entry list for the same hash bucket */
+#define HASH_LIMIT 64
#define GR_PRIME 0x9e370001
#define HASH(v, shift) (((unsigned int)(v) * GR_PRIME) >> (shift))
-struct index {
+struct index_entry {
const unsigned char *ptr;
unsigned int val;
- struct index *next;
+ struct index_entry *next;
};
-static struct index ** delta_index(const unsigned char *buf,
- unsigned long bufsize,
- unsigned long trg_bufsize,
- unsigned int *hash_shift)
+struct delta_index {
+ const void *src_buf;
+ unsigned long src_size;
+ unsigned int hash_shift;
+ struct index_entry *hash[0];
+};
+
+struct delta_index * create_delta_index(const void *buf, unsigned long bufsize)
{
- unsigned int i, hsize, hshift, hlimit, entries, *hash_count;
- const unsigned char *data;
- struct index *entry, **hash;
+ unsigned int i, hsize, hshift, entries, *hash_count;
+ const unsigned char *data, *buffer = buf;
+ struct delta_index *index;
+ struct index_entry *entry, **hash;
void *mem;
+ if (!buf || !bufsize)
+ return NULL;
+
/* 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));
+ mem = malloc(sizeof(*index) +
+ sizeof(*hash) * hsize +
+ sizeof(*entry) * entries);
if (!mem)
return NULL;
+ index = mem;
+ mem = index + 1;
hash = mem;
- entry = mem + hsize * sizeof(*hash);
+ mem = hash + hsize;
+ entry = mem;
+
+ index->src_buf = buf;
+ index->src_size = bufsize;
+ index->hash_shift = hshift;
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);
+ free(index);
return NULL;
}
/* then populate the index */
- data = buf + entries * BLK_SIZE - BLK_SIZE;
- while (data >= buf) {
+ data = buffer + entries * BLK_SIZE - BLK_SIZE;
+ while (data >= buffer) {
unsigned int val = adler32(0, data, BLK_SIZE);
i = HASH(val, hshift);
entry->ptr = data;
@@ -91,27 +108,18 @@ static struct index ** delta_index(const
* 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
+ * 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)
+ if (hash_count[i] < HASH_LIMIT)
continue;
entry = hash[i];
do {
- struct index *keep = entry;
- int skip = hash_count[i] / hlimit / 2;
+ struct index_entry *keep = entry;
+ int skip = hash_count[i] / HASH_LIMIT / 2;
do {
entry = entry->next;
} while(--skip && entry);
@@ -120,7 +128,12 @@ static struct index ** delta_index(const
}
free(hash_count);
- return hash;
+ return index;
+}
+
+void free_delta_index(struct delta_index *index)
+{
+ free(index);
}
/* provide the size of the copy opcode given the block offset and size */
@@ -131,21 +144,17 @@ #define COPYOP_SIZE(o, s) \
/* 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)
+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, 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)
+ if (!trg_buf || !trg_size)
return NULL;
outpos = 0;
@@ -153,60 +162,55 @@ void *diff_delta(void *from_buf, unsigne
if (max_size && outsize >= max_size)
outsize = max_size + MAX_OP_SIZE + 1;
out = malloc(outsize);
- if (!out) {
- free(hash);
+ if (!out)
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;
+ i = index->src_size;
+ while (i >= 0x80) {
+ out[outpos++] = i | 0x80;
+ i >>= 7;
}
+ out[outpos++] = i;
/* 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;
+ 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;
+ hash_shift = index->hash_shift;
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;
- }
+ struct index_entry *entry;
+ unsigned int val = adler32(0, data, BLK_SIZE);
+ i = HASH(val, hash_shift);
+ 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;
}
}
@@ -271,7 +275,6 @@ void *diff_delta(void *from_buf, unsigne
out = realloc(out, outsize);
if (!out) {
free(tmp);
- free(hash);
return NULL;
}
}
@@ -280,7 +283,6 @@ void *diff_delta(void *from_buf, unsigne
if (inscnt)
out[outpos - inscnt - 1] = inscnt;
- free(hash);
*delta_size = outpos;
return out;
}
diff --git a/patch-delta.c b/patch-delta.c
index d95f0d9..8f318ed 100644
--- a/patch-delta.c
+++ b/patch-delta.c
@@ -13,8 +13,8 @@ #include <stdlib.h>
#include <string.h>
#include "delta.h"
-void *patch_delta(void *src_buf, unsigned long src_size,
- void *delta_buf, unsigned long delta_size,
+void *patch_delta(const void *src_buf, unsigned long src_size,
+ const void *delta_buf, unsigned long delta_size,
unsigned long *dst_size)
{
const unsigned char *data, *top;
-
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