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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 "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, b) (((unsigned int)(v) * GR_PRIME) >> (32 - (b)))
/* largest prime smaller than 65536 */
#define BASE 65521
/* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
#define NMAX 5552
#define DO1(buf, i) { s1 += buf[i]; s2 += s1; }
#define DO2(buf, i) DO1(buf, i); DO1(buf, i + 1);
#define DO4(buf, i) DO2(buf, i); DO2(buf, i + 2);
#define DO8(buf, i) DO4(buf, i); DO4(buf, i + 4);
#define DO16(buf) DO8(buf, 0); DO8(buf, 8);
static unsigned int adler32(unsigned int adler, const unsigned char *buf, int len)
{
int k;
unsigned int s1 = adler & 0xffff;
unsigned int s2 = adler >> 16;
while (len > 0) {
k = MIN(len, NMAX);
len -= k;
while (k >= 16) {
DO16(buf);
buf += 16;
k -= 16;
}
if (k != 0)
do {
s1 += *buf++;
s2 += s1;
} while (--k);
s1 %= BASE;
s2 %= BASE;
}
return (s2 << 16) | s1;
}
static unsigned int hashbits(unsigned int size)
{
unsigned int val = 1, bits = 0;
while (val < size && bits < 32) {
val <<= 1;
bits++;
}
return bits ? bits: 1;
}
typedef struct s_chanode {
struct s_chanode *next;
int icurr;
} chanode_t;
typedef struct s_chastore {
int isize, nsize;
chanode_t *ancur;
} chastore_t;
static void cha_init(chastore_t *cha, int isize, int icount)
{
cha->isize = isize;
cha->nsize = icount * isize;
cha->ancur = NULL;
}
static void *cha_alloc(chastore_t *cha)
{
chanode_t *ancur;
void *data;
ancur = cha->ancur;
if (!ancur || ancur->icurr == cha->nsize) {
ancur = malloc(sizeof(chanode_t) + cha->nsize);
if (!ancur)
return NULL;
ancur->icurr = 0;
ancur->next = cha->ancur;
cha->ancur = ancur;
}
data = (void *)ancur + sizeof(chanode_t) + ancur->icurr;
ancur->icurr += cha->isize;
return data;
}
static void cha_free(chastore_t *cha)
{
chanode_t *cur = cha->ancur;
while (cur) {
chanode_t *tmp = cur;
cur = cur->next;
free(tmp);
}
}
typedef struct s_bdrecord {
struct s_bdrecord *next;
unsigned int fp;
const unsigned char *ptr;
} bdrecord_t;
typedef struct s_bdfile {
chastore_t cha;
unsigned int fphbits;
bdrecord_t **fphash;
} bdfile_t;
static int delta_prepare(const unsigned char *buf, int bufsize, bdfile_t *bdf)
{
unsigned int fphbits;
int i, hsize;
const unsigned char *data, *top;
bdrecord_t *brec;
bdrecord_t **fphash;
fphbits = hashbits(bufsize / BLK_SIZE + 1);
hsize = 1 << fphbits;
fphash = malloc(hsize * sizeof(bdrecord_t *));
if (!fphash)
return -1;
for (i = 0; i < hsize; i++)
fphash[i] = NULL;
cha_init(&bdf->cha, sizeof(bdrecord_t), hsize / 4 + 1);
top = buf + bufsize;
data = buf + (bufsize / BLK_SIZE) * BLK_SIZE;
if (data == top)
data -= BLK_SIZE;
for ( ; data >= buf; data -= BLK_SIZE) {
brec = cha_alloc(&bdf->cha);
if (!brec) {
cha_free(&bdf->cha);
free(fphash);
return -1;
}
brec->fp = adler32(0, data, MIN(BLK_SIZE, top - data));
brec->ptr = data;
i = HASH(brec->fp, fphbits);
brec->next = fphash[i];
fphash[i] = brec;
}
bdf->fphbits = fphbits;
bdf->fphash = fphash;
return 0;
}
static void delta_cleanup(bdfile_t *bdf)
{
free(bdf->fphash);
cha_free(&bdf->cha);
}
#define COPYOP_SIZE(o, s) \
(!!(o & 0xff) + !!(o & 0xff00) + !!(o & 0xff0000) + !!(o & 0xff000000) + \
!!(s & 0xff) + !!(s & 0xff00) + 1)
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)
{
int i, outpos, outsize, inscnt, csize, msize, moff;
unsigned int fp;
const unsigned char *ref_data, *ref_top, *data, *top, *ptr1, *ptr2;
unsigned char *out, *orig;
bdrecord_t *brec;
bdfile_t bdf;
if (!from_size || !to_size || delta_prepare(from_buf, from_size, &bdf))
return NULL;
outpos = 0;
outsize = 8192;
out = malloc(outsize);
if (!out) {
delta_cleanup(&bdf);
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;
moff = 0;
while (data < top) {
msize = 0;
fp = adler32(0, data, MIN(top - data, BLK_SIZE));
i = HASH(fp, bdf.fphbits);
for (brec = bdf.fphash[i]; brec; brec = brec->next) {
if (brec->fp == fp) {
csize = ref_top - brec->ptr;
if (csize > top - data)
csize = top - data;
for (ptr1 = brec->ptr, ptr2 = data;
csize && *ptr1 == *ptr2;
csize--, ptr1++, ptr2++);
csize = ptr1 - brec->ptr;
if (csize > msize) {
moff = brec->ptr - ref_data;
msize = csize;
if (msize >= 0x10000) {
msize = 0x10000;
break;
}
}
}
}
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 {
if (inscnt) {
out[outpos - inscnt - 1] = inscnt;
inscnt = 0;
}
data += msize;
orig = 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; }
*orig = i;
}
if (max_size && outpos > max_size) {
free(out);
delta_cleanup(&bdf);
return NULL;
}
/* next time around the largest possible output is 1 + 4 + 3 */
if (outpos > outsize - 8) {
void *tmp = out;
outsize = outsize * 3 / 2;
out = realloc(out, outsize);
if (!out) {
free(tmp);
delta_cleanup(&bdf);
return NULL;
}
}
}
if (inscnt)
out[outpos - inscnt - 1] = inscnt;
delta_cleanup(&bdf);
*delta_size = outpos;
return out;
}
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