/* 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 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 hsize, hshift, entries, blksize, i;
- 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 - 1) / BLK_SIZE;
+ entries = bufsize / BLK_SIZE;
hsize = entries / 4;
- for (i = 4; (1 << i) < hsize && i < 16; i++);
+ 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));
- /* then populate it */
- data = buf + entries * BLK_SIZE - BLK_SIZE;
- blksize = bufsize - (data - buf);
- while (data >= buf) {
- unsigned int val = adler32(0, data, blksize);
+ /* 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 */
+ 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;
entry->val = val;
entry->next = hash[i];
hash[i] = entry++;
- blksize = BLK_SIZE;
+ hash_count[i]++;
data -= BLK_SIZE;
}
- return hash;
+ /*
+ * 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);
+
+ 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 */
/* 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, inscnt, hash_shift;
+ 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, &hash_shift);
- if (!hash)
+ if (!trg_buf || !trg_size)
return NULL;
outpos = 0;
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;
- unsigned int blksize = MIN(top - data, BLK_SIZE);
- unsigned int val = adler32(0, data, blksize);
+ struct index_entry *entry;
+ unsigned int val = adler32(0, data, BLK_SIZE);
i = HASH(val, hash_shift);
- for (entry = hash[i]; entry; entry = entry->next) {
+ 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;
continue;
if (ref_size > top - src)
ref_size = top - src;
- while (ref_size && *src++ == *ref) {
+ if (ref_size > 0x10000)
+ ref_size = 0x10000;
+ if (ref_size <= msize)
+ break;
+ while (ref_size-- && *src++ == *ref)
ref++;
- ref_size--;
- }
- ref_size = ref - entry->ptr;
- if (ref_size > msize) {
+ if (msize < ref - entry->ptr) {
/* this is our best match so far */
+ msize = ref - entry->ptr;
moff = entry->ptr - ref_data;
- msize = ref_size;
- if (msize >= 0x10000) {
- msize = 0x10000;
- break;
- }
}
}
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;
}
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;
}
projects / git.git / blobdiff