#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 long trg_bufsize,
+ unsigned int *hash_shift)
{
- unsigned long hsize;
- unsigned int i, hshift, hlimit, *hash_count;
+ unsigned int i, hsize, hshift, hlimit, entries, *hash_count;
const unsigned char *data;
struct index *entry, **hash;
void *mem;
/* determine index hash size */
- hsize = bufsize / 4;
- for (i = 8; (1 << i) < hsize && i < 24; i += 2);
+ entries = bufsize / BLK_SIZE;
+ hsize = entries / 4;
+ for (i = 4; (1 << i) < hsize && i < 31; i++);
hsize = 1 << i;
- hshift = (i - 8) / 2;
+ hshift = 32 - i;
+ *hash_shift = hshift;
- /*
- * Allocate lookup index. Note the first hash pointer
- * is used to store the hash shift value.
- */
- mem = malloc((1 + hsize) * sizeof(*hash) + bufsize * sizeof(*entry));
+ /* allocate lookup index */
+ mem = malloc(hsize * sizeof(*hash) + entries * sizeof(*entry));
if (!mem)
return NULL;
hash = mem;
- *hash++ = (void *)hshift;
- entry = mem + (1 + hsize) * sizeof(*hash);
+ entry = mem + hsize * sizeof(*hash);
memset(hash, 0, hsize * sizeof(*hash));
/* allocate an array to count hash entries */
}
/* then populate the index */
- data = buf + bufsize - 2;
- while (data > buf) {
- entry->ptr = --data;
- i = data[0] ^ ((data[1] ^ (data[2] << hshift)) << hshift);
+ 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;
}
/*
* the cost is bounded to something more like O(m+n).
*/
hlimit = (1 << 26) / trg_bufsize;
- if (hlimit < 16)
- hlimit = 16;
+ 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 short-circuit the entry
- * list uniformly to still preserve a good repartition across
+ * 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++) {
}
free(hash_count);
- return hash-1;
+ return hash;
}
/* provide the size of the copy opcode given the block offset and size */
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 **from_index)
+ unsigned long max_size)
{
unsigned int i, outpos, outsize, inscnt, hash_shift;
const unsigned char *ref_data, *ref_top, *data, *top;
if (!from_size || !to_size)
return NULL;
- if (from_index && *from_index) {
- hash = *from_index;
- } else {
- hash = delta_index(from_buf, from_size, to_size);
- if (!hash)
- return NULL;
- if (from_index)
- *from_index = hash;
- }
- hash_shift = (unsigned int)(*hash++);
+ hash = delta_index(from_buf, from_size, to_size, &hash_shift);
+ if (!hash)
+ return NULL;
outpos = 0;
outsize = 8192;
outsize = max_size + MAX_OP_SIZE + 1;
out = malloc(outsize);
if (!out) {
- if (!from_index)
- free(hash-1);
+ free(hash);
return NULL;
}
while (data < top) {
unsigned int moff = 0, msize = 0;
- if (data + 3 <= top) {
- i = data[0] ^ ((data[1] ^ (data[2] << hash_shift)) << hash_shift);
+ 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;
- if (*ref != *src)
- continue;
- while (ref_size-- && *++src == *++ref);
+ while (ref_size-- && *src++ == *ref)
+ ref++;
if (msize < ref - entry->ptr) {
/* this is our best match so far */
msize = ref - entry->ptr;
out = realloc(out, outsize);
if (!out) {
free(tmp);
- if (!from_index)
- free(hash-1);
+ free(hash);
return NULL;
}
}
if (inscnt)
out[outpos - inscnt - 1] = inscnt;
- if (!from_index)
- free(hash-1);
+ free(hash);
*delta_size = outpos;
return out;
}