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75c42d8cc3
Anything that generates a delta to see if two objects are close usually isn't interested in the delta ends up being bigger than some specified size, and this allows us to stop delta generation early when that happens.
365 lines
9.3 KiB
C
365 lines
9.3 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(unsigned char *buf, unsigned long len,
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char *hdr, int hdrlen, unsigned long *retsize)
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{
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unsigned 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 = (unsigned char *)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(unsigned 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(unsigned 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 void *get_buffer(unsigned char *sha1, char *type,
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unsigned long *size, unsigned long *compsize)
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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 (compsize)
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*compsize = 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 *size, char *type,
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unsigned int *depth, unsigned char **links)
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{
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void *buf = NULL;
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unsigned int level = (*depth)++;
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if (*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, NULL);
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if (ref && !strcmp(type, "delta"))
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ref = expand_delta(ref, &ref_size, type, depth, links);
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else if (ref)
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{
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*links = xmalloc(*depth * 20);
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}
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if (ref) {
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buf = patch_delta(ref, ref_size, delta+20, *size-20, size);
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free(ref);
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if (buf)
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memcpy(*links + level*20, delta, 20);
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else
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free(*links);
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}
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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] [--max-behind=N] <reference_sha1> <target_sha1> [<next_sha1> ...]";
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struct delta {
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unsigned char sha1[20]; /* object sha1 */
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unsigned long size; /* object size */
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void *buf; /* object content */
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unsigned char *links; /* delta reference links */
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unsigned int depth; /* delta depth */
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};
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int main(int argc, char **argv)
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{
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struct delta *ref, trg;
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char ref_type[20], trg_type[20], *skip_reason;
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void *best_buf;
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unsigned long best_size, orig_size, orig_compsize;
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unsigned int r, orig_ref, best_ref, nb_refs, next_ref, max_refs = 0;
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unsigned int i, duplicate, skip_lvl, verbose = 0, quiet = 0;
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unsigned int max_depth = -1;
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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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quiet = 0;
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} else if (!strcmp(argv[i], "-q")) {
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quiet = 1;
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verbose = 0;
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} else if (!strcmp(argv[i], "-d") && i+1 < argc) {
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max_depth = atoi(argv[++i]);
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} else if (!strncmp(argv[i], "--max-depth=", 12)) {
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max_depth = atoi(argv[i]+12);
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} else if (!strcmp(argv[i], "-b") && i+1 < argc) {
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max_refs = atoi(argv[++i]);
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} else if (!strncmp(argv[i], "--max-behind=", 13)) {
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max_refs = atoi(argv[i]+13);
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} else
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break;
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}
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if (i + (max_depth != 0) >= argc)
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usage(mkdelta_usage);
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if (!max_refs || max_refs > argc - i)
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max_refs = argc - i;
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ref = xmalloc(max_refs * sizeof(*ref));
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for (r = 0; r < max_refs; r++)
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ref[r].buf = ref[r].links = NULL;
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next_ref = nb_refs = 0;
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do {
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if (get_sha1(argv[i], trg.sha1))
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die("bad sha1 %s", argv[i]);
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trg.buf = get_buffer(trg.sha1, trg_type, &trg.size, &orig_compsize);
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if (trg.buf && !trg.size) {
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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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orig_size = trg.size;
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orig_ref = -1;
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trg.depth = 0;
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trg.links = NULL;
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if (trg.buf && !strcmp(trg_type, "delta")) {
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for (r = 0; r < nb_refs; r++)
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if (!memcmp(trg.buf, ref[r].sha1, 20))
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break;
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if (r < nb_refs) {
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/* no need to reload the reference object */
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trg.depth = ref[r].depth + 1;
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trg.links = xmalloc(trg.depth*20);
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memcpy(trg.links, trg.buf, 20);
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memcpy(trg.links+20, ref[r].links, ref[r].depth*20);
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trg.buf = patch_delta(ref[r].buf, ref[r].size,
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trg.buf+20, trg.size-20,
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&trg.size);
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strcpy(trg_type, ref_type);
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orig_ref = r;
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} else {
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trg.buf = expand_delta(trg.buf, &trg.size, trg_type,
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&trg.depth, &trg.links);
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}
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}
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if (!trg.buf)
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die("unable to read target object %s", argv[i]);
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if (!nb_refs) {
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strcpy(ref_type, trg_type);
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} else if (max_depth && strcmp(ref_type, trg_type)) {
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die("type mismatch for object %s", argv[i]);
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}
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duplicate = 0;
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best_buf = NULL;
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best_size = -1;
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best_ref = -1;
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skip_lvl = 0;
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skip_reason = NULL;
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for (r = 0; max_depth && r < nb_refs; r++) {
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void *delta_buf, *comp_buf;
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unsigned long delta_size, comp_size;
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unsigned int l;
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duplicate = !memcmp(trg.sha1, ref[r].sha1, 20);
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if (duplicate) {
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skip_reason = "already seen";
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break;
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}
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if (ref[r].depth >= max_depth) {
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if (skip_lvl < 1) {
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skip_reason = "exceeding max link depth";
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skip_lvl = 1;
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}
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continue;
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}
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for (l = 0; l < ref[r].depth; l++)
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if (!memcmp(trg.sha1, ref[r].links + l*20, 20))
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break;
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if (l != ref[r].depth) {
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if (skip_lvl < 2) {
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skip_reason = "would create a loop";
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skip_lvl = 2;
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}
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continue;
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}
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if (trg.depth < max_depth && r == orig_ref) {
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if (skip_lvl < 3) {
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skip_reason = "delta already in place";
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skip_lvl = 3;
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}
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continue;
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}
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delta_buf = diff_delta(ref[r].buf, ref[r].size,
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trg.buf, trg.size,
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&delta_size, ~0UL);
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if (!delta_buf)
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die("out of memory");
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if (trg.depth < max_depth &&
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delta_size+20 >= orig_size) {
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/* no need to even try to compress if original
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object is smaller than this delta */
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free(delta_buf);
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if (skip_lvl < 4) {
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skip_reason = "no size reduction";
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skip_lvl = 4;
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}
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continue;
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}
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comp_buf = create_delta_object(delta_buf, delta_size,
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ref[r].sha1, &comp_size);
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if (!comp_buf)
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die("out of memory");
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free(delta_buf);
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if (trg.depth < max_depth &&
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comp_size >= orig_compsize) {
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free(comp_buf);
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if (skip_lvl < 5) {
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skip_reason = "no size reduction";
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skip_lvl = 5;
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}
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continue;
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}
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if ((comp_size < best_size) ||
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(comp_size == best_size &&
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ref[r].depth < ref[best_ref].depth)) {
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free(best_buf);
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best_buf = comp_buf;
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best_size = comp_size;
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best_ref = r;
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}
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}
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if (best_buf) {
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if (replace_object(best_buf, best_size, trg.sha1))
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die("unable to write delta for %s", argv[i]);
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free(best_buf);
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free(trg.links);
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trg.depth = ref[best_ref].depth + 1;
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trg.links = xmalloc(trg.depth*20);
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memcpy(trg.links, ref[best_ref].sha1, 20);
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memcpy(trg.links+20, ref[best_ref].links, ref[best_ref].depth*20);
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if (!quiet)
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printf("delta %s (size=%ld.%02ld%% depth=%d dist=%d)\n",
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argv[i], best_size*100 / orig_compsize,
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(best_size*10000 / orig_compsize)%100,
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trg.depth,
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(next_ref - best_ref + max_refs)
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% (max_refs + 1) + 1);
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} else if (trg.depth > max_depth) {
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if (restore_original_object(trg.buf, trg.size, trg_type, trg.sha1))
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die("unable to restore %s", argv[i]);
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if (!quiet)
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printf("undelta %s (depth was %d)\n",
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argv[i], trg.depth);
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trg.depth = 0;
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free(trg.links);
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trg.links = NULL;
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} else if (skip_reason && verbose) {
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printf("skip %s (%s)\n", argv[i], skip_reason);
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}
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if (!duplicate) {
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free(ref[next_ref].buf);
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free(ref[next_ref].links);
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ref[next_ref] = trg;
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if (++next_ref > nb_refs)
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nb_refs = next_ref;
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if (next_ref == max_refs)
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next_ref = 0;
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} else {
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free(trg.buf);
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free(trg.links);
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}
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} while (++i < argc);
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return 0;
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}
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