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-rw-r--r--diff-delta.c333
1 files changed, 333 insertions, 0 deletions
diff --git a/diff-delta.c b/diff-delta.c
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+++ b/diff-delta.c
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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 {
+ chanode_t *head, *tail;
+ int isize, nsize;
+ chanode_t *ancur;
+ chanode_t *sncur;
+ int scurr;
+} chastore_t;
+
+static void cha_init(chastore_t *cha, int isize, int icount)
+{
+ cha->head = cha->tail = NULL;
+ cha->isize = isize;
+ cha->nsize = icount * isize;
+ cha->ancur = cha->sncur = NULL;
+ cha->scurr = 0;
+}
+
+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 = NULL;
+ if (cha->tail)
+ cha->tail->next = ancur;
+ if (!cha->head)
+ cha->head = ancur;
+ cha->tail = 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->head;
+ 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 {
+ const unsigned char *data, *top;
+ 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 *base, *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);
+
+ bdf->data = data = base = buf;
+ bdf->top = top = buf + bufsize;
+ data += (bufsize / BLK_SIZE) * BLK_SIZE;
+ if (data == top)
+ data -= BLK_SIZE;
+
+ for ( ; data >= base; 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)
+{
+ int i, outpos, outsize, inscnt, csize, msize, moff;
+ unsigned int fp;
+ const unsigned char *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;
+ }
+
+ data = to_buf;
+ top = to_buf + to_size;
+
+ /* store reference buffer size */
+ orig = out + outpos++;
+ *orig = i = 0;
+ do {
+ if (from_size & 0xff) {
+ *orig |= (1 << i);
+ out[outpos++] = from_size;
+ }
+ i++;
+ from_size >>= 8;
+ } while (from_size);
+
+ /* store target buffer size */
+ orig = out + outpos++;
+ *orig = i = 0;
+ do {
+ if (to_size & 0xff) {
+ *orig |= (1 << i);
+ out[outpos++] = to_size;
+ }
+ i++;
+ to_size >>= 8;
+ } while (to_size);
+
+ 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 = bdf.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 - bdf.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;
+ }
+
+ /* 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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