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https://github.com/git/git.git
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e002a16ba5
This adds the ability to actually create delta objects using a new tool: git-mkdelta. It uses an ordered list of potential objects to deltafy against earlier objects in the list. A cap on the depth of delta references can be provided as well, otherwise the default is to not have any limit. A limit of 0 will also undeltafy any given object. Also provided is the beginning of a script to deltafy an entire repository. Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
318 lines
8.1 KiB
C
318 lines
8.1 KiB
C
/*
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* Deltafication of a GIT database.
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*
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* (C) 2005 Nicolas Pitre <nico@cam.org>
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*
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* This code is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*/
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#include "cache.h"
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#include "delta.h"
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static int replace_object(char *buf, unsigned long size, unsigned char *sha1)
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{
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char tmpfile[PATH_MAX];
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int fd;
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snprintf(tmpfile, sizeof(tmpfile), "%s/obj_XXXXXX", get_object_directory());
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fd = mkstemp(tmpfile);
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if (fd < 0)
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return error("%s: %s\n", tmpfile, strerror(errno));
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if (write(fd, buf, size) != size) {
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perror("unable to write file");
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close(fd);
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unlink(tmpfile);
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return -1;
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}
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fchmod(fd, 0444);
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close(fd);
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if (rename(tmpfile, sha1_file_name(sha1))) {
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perror("unable to replace original object");
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unlink(tmpfile);
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return -1;
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}
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return 0;
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}
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static void *create_object(char *buf, unsigned long len, char *hdr, int hdrlen,
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unsigned long *retsize)
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{
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char *compressed;
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unsigned long size;
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z_stream stream;
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/* Set it up */
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memset(&stream, 0, sizeof(stream));
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deflateInit(&stream, Z_BEST_COMPRESSION);
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size = deflateBound(&stream, len+hdrlen);
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compressed = xmalloc(size);
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/* Compress it */
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stream.next_out = compressed;
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stream.avail_out = size;
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/* First header.. */
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stream.next_in = hdr;
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stream.avail_in = hdrlen;
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while (deflate(&stream, 0) == Z_OK)
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/* nothing */;
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/* Then the data itself.. */
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stream.next_in = buf;
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stream.avail_in = len;
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while (deflate(&stream, Z_FINISH) == Z_OK)
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/* nothing */;
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deflateEnd(&stream);
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*retsize = stream.total_out;
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return compressed;
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}
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static int restore_original_object(char *buf, unsigned long len,
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char *type, unsigned char *sha1)
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{
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char hdr[50];
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int hdrlen, ret;
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void *compressed;
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unsigned long size;
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hdrlen = sprintf(hdr, "%s %lu", type, len)+1;
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compressed = create_object(buf, len, hdr, hdrlen, &size);
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ret = replace_object(compressed, size, sha1);
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free(compressed);
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return ret;
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}
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static void *create_delta_object(char *buf, unsigned long len,
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unsigned char *sha1_ref, unsigned long *size)
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{
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char hdr[50];
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int hdrlen;
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/* Generate the header + sha1 of reference for delta */
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hdrlen = sprintf(hdr, "delta %lu", len+20)+1;
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memcpy(hdr + hdrlen, sha1_ref, 20);
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hdrlen += 20;
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return create_object(buf, len, hdr, hdrlen, size);
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}
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static unsigned long get_object_size(unsigned char *sha1)
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{
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struct stat st;
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if (stat(sha1_file_name(sha1), &st))
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die("%s: %s", sha1_to_hex(sha1), strerror(errno));
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return st.st_size;
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}
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static void *get_buffer(unsigned char *sha1, char *type, unsigned long *size)
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{
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unsigned long mapsize;
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void *map = map_sha1_file(sha1, &mapsize);
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if (map) {
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void *buffer = unpack_sha1_file(map, mapsize, type, size);
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munmap(map, mapsize);
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if (buffer)
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return buffer;
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}
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error("unable to get object %s", sha1_to_hex(sha1));
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return NULL;
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}
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static void *expand_delta(void *delta, unsigned long delta_size, char *type,
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unsigned long *size, unsigned int *depth, char *head)
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{
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void *buf = NULL;
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*depth++;
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if (delta_size < 20) {
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error("delta object is bad");
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free(delta);
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} else {
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unsigned long ref_size;
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void *ref = get_buffer(delta, type, &ref_size);
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if (ref && !strcmp(type, "delta"))
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ref = expand_delta(ref, ref_size, type, &ref_size,
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depth, head);
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else
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memcpy(head, delta, 20);
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if (ref)
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buf = patch_delta(ref, ref_size, delta+20,
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delta_size-20, size);
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free(ref);
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free(delta);
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}
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return buf;
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}
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static char *mkdelta_usage =
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"mkdelta [ --max-depth=N ] <reference_sha1> <target_sha1> [ <next_sha1> ... ]";
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int main(int argc, char **argv)
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{
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unsigned char sha1_ref[20], sha1_trg[20], head_ref[20], head_trg[20];
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char type_ref[20], type_trg[20];
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void *buf_ref, *buf_trg, *buf_delta;
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unsigned long size_ref, size_trg, size_orig, size_delta;
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unsigned int depth_ref, depth_trg, depth_max = -1;
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int i, verbose = 0;
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for (i = 1; i < argc; i++) {
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if (!strcmp(argv[i], "-v")) {
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verbose = 1;
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} else if (!strcmp(argv[i], "-d") && i+1 < argc) {
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depth_max = atoi(argv[++i]);
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} else if (!strncmp(argv[i], "--max-depth=", 12)) {
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depth_max = atoi(argv[i]+12);
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} else
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break;
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}
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if (i + (depth_max != 0) >= argc)
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usage(mkdelta_usage);
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if (get_sha1(argv[i], sha1_ref))
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die("bad sha1 %s", argv[i]);
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depth_ref = 0;
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buf_ref = get_buffer(sha1_ref, type_ref, &size_ref);
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if (buf_ref && !strcmp(type_ref, "delta"))
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buf_ref = expand_delta(buf_ref, size_ref, type_ref,
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&size_ref, &depth_ref, head_ref);
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else
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memcpy(head_ref, sha1_ref, 20);
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if (!buf_ref)
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die("unable to obtain initial object %s", argv[i]);
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if (depth_ref > depth_max) {
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if (restore_original_object(buf_ref, size_ref, type_ref, sha1_ref))
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die("unable to restore %s", argv[i]);
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if (verbose)
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printf("undelta %s (depth was %d)\n", argv[i], depth_ref);
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depth_ref = 0;
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}
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/*
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* TODO: deltafication should be tried against any early object
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* in the object list and not only the previous object.
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*/
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while (++i < argc) {
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if (get_sha1(argv[i], sha1_trg))
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die("bad sha1 %s", argv[i]);
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depth_trg = 0;
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buf_trg = get_buffer(sha1_trg, type_trg, &size_trg);
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if (buf_trg && !size_trg) {
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if (verbose)
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printf("skip %s (object is empty)\n", argv[i]);
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continue;
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}
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size_orig = size_trg;
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if (buf_trg && !strcmp(type_trg, "delta")) {
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if (!memcmp(buf_trg, sha1_ref, 20)) {
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/* delta already in place */
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depth_ref++;
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memcpy(sha1_ref, sha1_trg, 20);
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buf_ref = patch_delta(buf_ref, size_ref,
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buf_trg+20, size_trg-20,
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&size_ref);
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if (!buf_ref)
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die("unable to apply delta %s", argv[i]);
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if (depth_ref > depth_max) {
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if (restore_original_object(buf_ref, size_ref,
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type_ref, sha1_ref))
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die("unable to restore %s", argv[i]);
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if (verbose)
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printf("undelta %s (depth was %d)\n", argv[i], depth_ref);
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depth_ref = 0;
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continue;
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}
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if (verbose)
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printf("skip %s (delta already in place)\n", argv[i]);
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continue;
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}
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buf_trg = expand_delta(buf_trg, size_trg, type_trg,
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&size_trg, &depth_trg, head_trg);
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} else
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memcpy(head_trg, sha1_trg, 20);
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if (!buf_trg)
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die("unable to read target object %s", argv[i]);
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if (depth_trg > depth_max) {
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if (restore_original_object(buf_trg, size_trg, type_trg, sha1_trg))
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die("unable to restore %s", argv[i]);
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if (verbose)
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printf("undelta %s (depth was %d)\n", argv[i], depth_trg);
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depth_trg = 0;
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size_orig = size_trg;
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}
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if (depth_max == 0)
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goto skip;
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if (strcmp(type_ref, type_trg))
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die("type mismatch for object %s", argv[i]);
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if (!size_ref) {
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if (verbose)
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printf("skip %s (initial object is empty)\n", argv[i]);
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goto skip;
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}
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if (depth_ref + 1 > depth_max) {
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if (verbose)
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printf("skip %s (exceeding max link depth)\n", argv[i]);
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goto skip;
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}
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if (!memcmp(head_ref, sha1_trg, 20)) {
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if (verbose)
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printf("skip %s (would create a loop)\n", argv[i]);
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goto skip;
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}
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buf_delta = diff_delta(buf_ref, size_ref, buf_trg, size_trg, &size_delta);
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if (!buf_delta)
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die("out of memory");
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/* no need to even try to compress if original
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uncompressed is already smaller */
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if (size_delta+20 < size_orig) {
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void *buf_obj;
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unsigned long size_obj;
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buf_obj = create_delta_object(buf_delta, size_delta,
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sha1_ref, &size_obj);
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free(buf_delta);
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size_orig = get_object_size(sha1_trg);
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if (size_obj >= size_orig) {
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free(buf_obj);
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if (verbose)
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printf("skip %s (original is smaller)\n", argv[i]);
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goto skip;
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}
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if (replace_object(buf_obj, size_obj, sha1_trg))
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die("unable to write delta for %s", argv[i]);
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free(buf_obj);
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depth_ref++;
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if (verbose)
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printf("delta %s (size=%ld.%02ld%%, depth=%d)\n",
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argv[i], size_obj*100 / size_orig,
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(size_obj*10000 / size_orig)%100,
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depth_ref);
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} else {
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free(buf_delta);
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if (verbose)
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printf("skip %s (original is smaller)\n", argv[i]);
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skip:
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depth_ref = depth_trg;
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memcpy(head_ref, head_trg, 20);
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}
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free(buf_ref);
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buf_ref = buf_trg;
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size_ref = size_trg;
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memcpy(sha1_ref, sha1_trg, 20);
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}
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return 0;
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}
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