335 lines
7.1 KiB
C
335 lines
7.1 KiB
C
/*
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* diff-delta.c: generate a delta between two buffers
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*
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* Many parts of this file have been lifted from LibXDiff version 0.10.
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* http://www.xmailserver.org/xdiff-lib.html
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*
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* LibXDiff was written by Davide Libenzi <davidel@xmailserver.org>
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* Copyright (C) 2003 Davide Libenzi
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*
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* Many mods for GIT usage by Nicolas Pitre <nico@cam.org>, (C) 2005.
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*
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* This file is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* Use of this within git automatically means that the LGPL
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* licensing gets turned into GPLv2 within this project.
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*/
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#include <stdlib.h>
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#include "delta.h"
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/* block size: min = 16, max = 64k, power of 2 */
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#define BLK_SIZE 16
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#define MIN(a, b) ((a) < (b) ? (a) : (b))
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#define GR_PRIME 0x9e370001
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#define HASH(v, b) (((unsigned int)(v) * GR_PRIME) >> (32 - (b)))
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/* largest prime smaller than 65536 */
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#define BASE 65521
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/* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
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#define NMAX 5552
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#define DO1(buf, i) { s1 += buf[i]; s2 += s1; }
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#define DO2(buf, i) DO1(buf, i); DO1(buf, i + 1);
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#define DO4(buf, i) DO2(buf, i); DO2(buf, i + 2);
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#define DO8(buf, i) DO4(buf, i); DO4(buf, i + 4);
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#define DO16(buf) DO8(buf, 0); DO8(buf, 8);
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static unsigned int adler32(unsigned int adler, const unsigned char *buf, int len)
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{
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int k;
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unsigned int s1 = adler & 0xffff;
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unsigned int s2 = adler >> 16;
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while (len > 0) {
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k = MIN(len, NMAX);
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len -= k;
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while (k >= 16) {
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DO16(buf);
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buf += 16;
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k -= 16;
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}
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if (k != 0)
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do {
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s1 += *buf++;
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s2 += s1;
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} while (--k);
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s1 %= BASE;
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s2 %= BASE;
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}
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return (s2 << 16) | s1;
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}
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static unsigned int hashbits(unsigned int size)
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{
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unsigned int val = 1, bits = 0;
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while (val < size && bits < 32) {
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val <<= 1;
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bits++;
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}
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return bits ? bits: 1;
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}
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typedef struct s_chanode {
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struct s_chanode *next;
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int icurr;
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} chanode_t;
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typedef struct s_chastore {
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chanode_t *head, *tail;
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int isize, nsize;
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chanode_t *ancur;
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chanode_t *sncur;
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int scurr;
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} chastore_t;
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static void cha_init(chastore_t *cha, int isize, int icount)
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{
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cha->head = cha->tail = NULL;
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cha->isize = isize;
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cha->nsize = icount * isize;
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cha->ancur = cha->sncur = NULL;
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cha->scurr = 0;
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}
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static void *cha_alloc(chastore_t *cha)
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{
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chanode_t *ancur;
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void *data;
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ancur = cha->ancur;
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if (!ancur || ancur->icurr == cha->nsize) {
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ancur = malloc(sizeof(chanode_t) + cha->nsize);
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if (!ancur)
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return NULL;
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ancur->icurr = 0;
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ancur->next = NULL;
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if (cha->tail)
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cha->tail->next = ancur;
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if (!cha->head)
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cha->head = ancur;
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cha->tail = ancur;
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cha->ancur = ancur;
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}
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data = (void *)ancur + sizeof(chanode_t) + ancur->icurr;
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ancur->icurr += cha->isize;
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return data;
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}
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static void cha_free(chastore_t *cha)
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{
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chanode_t *cur = cha->head;
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while (cur) {
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chanode_t *tmp = cur;
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cur = cur->next;
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free(tmp);
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}
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}
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typedef struct s_bdrecord {
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struct s_bdrecord *next;
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unsigned int fp;
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const unsigned char *ptr;
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} bdrecord_t;
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typedef struct s_bdfile {
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const unsigned char *data, *top;
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chastore_t cha;
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unsigned int fphbits;
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bdrecord_t **fphash;
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} bdfile_t;
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static int delta_prepare(const unsigned char *buf, int bufsize, bdfile_t *bdf)
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{
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unsigned int fphbits;
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int i, hsize;
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const unsigned char *base, *data, *top;
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bdrecord_t *brec;
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bdrecord_t **fphash;
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fphbits = hashbits(bufsize / BLK_SIZE + 1);
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hsize = 1 << fphbits;
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fphash = malloc(hsize * sizeof(bdrecord_t *));
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if (!fphash)
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return -1;
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for (i = 0; i < hsize; i++)
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fphash[i] = NULL;
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cha_init(&bdf->cha, sizeof(bdrecord_t), hsize / 4 + 1);
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bdf->data = data = base = buf;
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bdf->top = top = buf + bufsize;
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data += (bufsize / BLK_SIZE) * BLK_SIZE;
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if (data == top)
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data -= BLK_SIZE;
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for ( ; data >= base; data -= BLK_SIZE) {
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brec = cha_alloc(&bdf->cha);
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if (!brec) {
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cha_free(&bdf->cha);
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free(fphash);
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return -1;
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}
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brec->fp = adler32(0, data, MIN(BLK_SIZE, top - data));
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brec->ptr = data;
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i = HASH(brec->fp, fphbits);
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brec->next = fphash[i];
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fphash[i] = brec;
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}
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bdf->fphbits = fphbits;
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bdf->fphash = fphash;
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return 0;
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}
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static void delta_cleanup(bdfile_t *bdf)
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{
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free(bdf->fphash);
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cha_free(&bdf->cha);
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}
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#define COPYOP_SIZE(o, s) \
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(!!(o & 0xff) + !!(o & 0xff00) + !!(o & 0xff0000) + !!(o & 0xff000000) + \
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!!(s & 0xff) + !!(s & 0xff00) + 1)
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void *diff_delta(void *from_buf, unsigned long from_size,
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void *to_buf, unsigned long to_size,
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unsigned long *delta_size,
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unsigned long max_size)
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{
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int i, outpos, outsize, inscnt, csize, msize, moff;
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unsigned int fp;
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const unsigned char *data, *top, *ptr1, *ptr2;
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unsigned char *out, *orig;
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bdrecord_t *brec;
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bdfile_t bdf;
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if (!from_size || !to_size || delta_prepare(from_buf, from_size, &bdf))
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return NULL;
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outpos = 0;
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outsize = 8192;
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out = malloc(outsize);
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if (!out) {
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delta_cleanup(&bdf);
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return NULL;
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}
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data = to_buf;
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top = to_buf + to_size;
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/* store reference buffer size */
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out[outpos++] = from_size;
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from_size >>= 7;
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while (from_size) {
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out[outpos - 1] |= 0x80;
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out[outpos++] = from_size;
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from_size >>= 7;
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}
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/* store target buffer size */
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out[outpos++] = to_size;
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to_size >>= 7;
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while (to_size) {
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out[outpos - 1] |= 0x80;
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out[outpos++] = to_size;
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to_size >>= 7;
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}
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inscnt = 0;
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moff = 0;
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while (data < top) {
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msize = 0;
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fp = adler32(0, data, MIN(top - data, BLK_SIZE));
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i = HASH(fp, bdf.fphbits);
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for (brec = bdf.fphash[i]; brec; brec = brec->next) {
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if (brec->fp == fp) {
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csize = bdf.top - brec->ptr;
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if (csize > top - data)
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csize = top - data;
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for (ptr1 = brec->ptr, ptr2 = data;
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csize && *ptr1 == *ptr2;
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csize--, ptr1++, ptr2++);
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csize = ptr1 - brec->ptr;
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if (csize > msize) {
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moff = brec->ptr - bdf.data;
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msize = csize;
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if (msize >= 0x10000) {
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msize = 0x10000;
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break;
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}
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}
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}
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}
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if (!msize || msize < COPYOP_SIZE(moff, msize)) {
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if (!inscnt)
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outpos++;
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out[outpos++] = *data++;
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inscnt++;
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if (inscnt == 0x7f) {
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out[outpos - inscnt - 1] = inscnt;
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inscnt = 0;
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}
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} else {
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if (inscnt) {
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out[outpos - inscnt - 1] = inscnt;
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inscnt = 0;
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}
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data += msize;
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orig = out + outpos++;
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i = 0x80;
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if (moff & 0xff) { out[outpos++] = moff; i |= 0x01; }
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moff >>= 8;
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if (moff & 0xff) { out[outpos++] = moff; i |= 0x02; }
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moff >>= 8;
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if (moff & 0xff) { out[outpos++] = moff; i |= 0x04; }
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moff >>= 8;
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if (moff & 0xff) { out[outpos++] = moff; i |= 0x08; }
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if (msize & 0xff) { out[outpos++] = msize; i |= 0x10; }
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msize >>= 8;
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if (msize & 0xff) { out[outpos++] = msize; i |= 0x20; }
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*orig = i;
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}
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if (max_size && outpos > max_size) {
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free(out);
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delta_cleanup(&bdf);
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return NULL;
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}
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/* next time around the largest possible output is 1 + 4 + 3 */
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if (outpos > outsize - 8) {
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void *tmp = out;
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outsize = outsize * 3 / 2;
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out = realloc(out, outsize);
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if (!out) {
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free(tmp);
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delta_cleanup(&bdf);
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return NULL;
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}
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}
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}
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if (inscnt)
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out[outpos - inscnt - 1] = inscnt;
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delta_cleanup(&bdf);
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*delta_size = outpos;
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return out;
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}
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