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Revert "Revert "diff-delta: produce optimal pack data""

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This commit is contained in:
Junio C Hamano 2006-02-27 21:37:56 -08:00
parent eae3fe5e50
commit bec2a69fe4
1 changed files with 30 additions and 47 deletions
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77
diff-delta.c
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@ -20,21 +20,11 @@
#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;
};
@ -42,21 +32,21 @@ static struct index ** delta_index(const unsigned char *buf,
unsigned long bufsize,
unsigned int *hash_shift)
{
unsigned int hsize, hshift, entries, blksize, i;
unsigned long hsize;
unsigned int hshift, i;
const unsigned char *data;
struct index *entry, **hash;
void *mem;
/* determine index hash size */
entries = (bufsize + BLK_SIZE - 1) / BLK_SIZE;
hsize = entries / 4;
for (i = 4; (1 << i) < hsize && i < 16; i++);
hsize = bufsize / 4;
for (i = 8; (1 << i) < hsize && i < 16; i++);
hsize = 1 << i;
hshift = 32 - i;
hshift = i - 8;
*hash_shift = hshift;
/* allocate lookup index */
mem = malloc(hsize * sizeof(*hash) + entries * sizeof(*entry));
mem = malloc(hsize * sizeof(*hash) + bufsize * sizeof(*entry));
if (!mem)
return NULL;
hash = mem;
@ -64,17 +54,12 @@ static struct index ** delta_index(const unsigned char *buf,
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);
i = HASH(val, hshift);
entry->ptr = data;
entry->val = val;
data = buf + bufsize - 2;
while (data > buf) {
entry->ptr = --data;
i = data[0] ^ data[1] ^ (data[2] << hshift);
entry->next = hash[i];
hash[i] = entry++;
blksize = BLK_SIZE;
data -= BLK_SIZE;
}
return hash;
@ -141,29 +126,27 @@ void *diff_delta(void *from_buf, unsigned long from_size,
while (data < top) {
unsigned int moff = 0, msize = 0;
unsigned int blksize = MIN(top - data, BLK_SIZE);
unsigned int val = adler32(0, data, blksize);
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;
while (ref_size && *src++ == *ref) {
ref++;
ref_size--;
}
ref_size = ref - entry->ptr;
if (ref_size > msize) {
/* this is our best match so far */
moff = entry->ptr - ref_data;
msize = ref_size;
if (msize >= 0x10000) {
msize = 0x10000;
if (data + 2 < top) {
i = data[0] ^ data[1] ^ (data[2] << 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 (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++;
ref_size--;
}
ref_size = ref - entry->ptr;
if (msize < ref - entry->ptr) {
/* this is our best match so far */
msize = ref - entry->ptr;
moff = entry->ptr - ref_data;
}
}
}