c4fb06c0d0
This actually successfully packed and unpacked a git archive down to 1.3MB (17MB unpacked). Right now unpacking is way too noisy, lots of debug messages left.
421 lines
10 KiB
C
421 lines
10 KiB
C
#include "cache.h"
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#include "object.h"
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#include "delta.h"
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static const char pack_usage[] = "git-pack-objects [--window=N] [--depth=N] base-name < object-list";
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enum object_type {
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OBJ_NONE,
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OBJ_COMMIT,
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OBJ_TREE,
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OBJ_BLOB,
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OBJ_DELTA // NOTE! This is _not_ the same as a "delta" object in the filesystem
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};
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struct object_entry {
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unsigned char sha1[20];
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unsigned long size;
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unsigned long offset;
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unsigned int depth;
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unsigned int flags;
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enum object_type type;
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unsigned long delta_size;
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struct object_entry *delta;
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};
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static struct object_entry **sorted_by_sha, **sorted_by_type;
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static struct object_entry *objects = NULL;
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static int nr_objects = 0, nr_alloc = 0;
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static const char *base_name;
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struct myfile {
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int fd;
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unsigned long chars;
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unsigned char buffer[8192];
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};
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static FILE *create_file(const char *suffix)
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{
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static char filename[PATH_MAX];
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unsigned len;
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len = snprintf(filename, PATH_MAX, "%s.%s", base_name, suffix);
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if (len >= PATH_MAX)
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die("you wascally wabbit, you");
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return fopen(filename, "w");
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}
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static unsigned long fwrite_compressed(void *in, unsigned long size, FILE *f)
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{
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z_stream stream;
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unsigned long maxsize;
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void *out;
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memset(&stream, 0, sizeof(stream));
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deflateInit(&stream, Z_DEFAULT_COMPRESSION);
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maxsize = deflateBound(&stream, size);
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out = xmalloc(maxsize);
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/* Compress it */
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stream.next_in = in;
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stream.avail_in = size;
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stream.next_out = out;
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stream.avail_out = maxsize;
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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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size = stream.total_out;
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fwrite(out, size, 1, f);
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free(out);
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return size;
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}
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static void *delta_against(void *buf, unsigned long size, struct object_entry *entry)
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{
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unsigned long othersize, delta_size;
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char type[10];
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void *otherbuf = read_sha1_file(entry->delta->sha1, type, &othersize);
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void *delta_buf;
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if (!otherbuf)
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die("unable to read %s", sha1_to_hex(entry->delta->sha1));
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delta_buf = diff_delta(otherbuf, othersize,
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buf, size, &delta_size, ~0UL);
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if (!delta_buf || delta_size != entry->delta_size)
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die("delta size changed");
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free(buf);
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free(otherbuf);
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return delta_buf;
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}
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static unsigned long write_object(FILE *f, struct object_entry *entry)
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{
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unsigned long size;
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char type[10];
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void *buf = read_sha1_file(entry->sha1, type, &size);
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char header[25];
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unsigned hdrlen, datalen;
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if (!buf)
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die("unable to read %s", sha1_to_hex(entry->sha1));
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if (size != entry->size)
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die("object %s size inconsistency (%lu vs %lu)", sha1_to_hex(entry->sha1), size, entry->size);
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/*
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* The object header is a byte of 'type' followed by four bytes of
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* length, except for deltas that has the 20 bytes of delta sha
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* instead.
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*/
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header[0] = ".CTB"[entry->type];
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hdrlen = 5;
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if (entry->delta) {
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header[0] = 'D';
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memcpy(header+5, entry->delta, 20);
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buf = delta_against(buf, size, entry);
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size = entry->delta_size;
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hdrlen = 25;
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}
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datalen = htonl(size);
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memcpy(header+1, &datalen, 4);
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fwrite(header, hdrlen, 1, f);
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datalen = fwrite_compressed(buf, size, f);
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free(buf);
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return hdrlen + datalen;
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}
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static void write_pack_file(void)
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{
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int i;
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FILE *f = create_file("pack");
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unsigned long offset = 0;
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unsigned long mb;
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for (i = 0; i < nr_objects; i++) {
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struct object_entry *entry = objects + i;
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entry->offset = offset;
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offset += write_object(f, entry);
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}
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fclose(f);
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mb = offset >> 20;
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offset &= 0xfffff;
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}
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static void write_index_file(void)
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{
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int i;
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FILE *f = create_file("idx");
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struct object_entry **list = sorted_by_sha;
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struct object_entry **last = list + nr_objects;
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unsigned int array[256];
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/*
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* Write the first-level table (the list is sorted,
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* but we use a 256-entry lookup to be able to avoid
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* having to do eight extra binary search iterations)
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*/
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for (i = 0; i < 256; i++) {
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struct object_entry **next = list;
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while (next < last) {
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struct object_entry *entry = *next;
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if (entry->sha1[0] != i)
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break;
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next++;
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}
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array[i] = htonl(next - sorted_by_sha);
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list = next;
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}
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fwrite(array, 256, sizeof(int), f);
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/*
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* Write the actual SHA1 entries..
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*/
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list = sorted_by_sha;
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for (i = 0; i < nr_objects; i++) {
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struct object_entry *entry = *list++;
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unsigned int offset = htonl(entry->offset);
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fwrite(&offset, 4, 1, f);
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fwrite(entry->sha1, 20, 1, f);
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}
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fclose(f);
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}
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static void add_object_entry(unsigned char *sha1)
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{
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unsigned int idx = nr_objects;
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struct object_entry *entry;
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if (idx >= nr_alloc) {
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unsigned int needed = (idx + 1024) * 3 / 2;
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objects = xrealloc(objects, needed * sizeof(*entry));
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nr_alloc = needed;
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}
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entry = objects + idx;
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memset(entry, 0, sizeof(*entry));
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memcpy(entry->sha1, sha1, 20);
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nr_objects = idx+1;
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}
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static void check_object(struct object_entry *entry)
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{
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char buffer[128];
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char type[10];
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unsigned long mapsize;
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z_stream stream;
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void *map;
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map = map_sha1_file(entry->sha1, &mapsize);
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if (!map)
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die("unable to map %s", sha1_to_hex(entry->sha1));
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if (unpack_sha1_header(&stream, map, mapsize, buffer, sizeof(buffer)) < 0)
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die("unable to unpack %s header", sha1_to_hex(entry->sha1));
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munmap(map, mapsize);
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if (parse_sha1_header(buffer, type, &entry->size) < 0)
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die("unable to parse %s header", sha1_to_hex(entry->sha1));
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if (!strcmp(type, "commit")) {
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entry->type = OBJ_COMMIT;
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} else if (!strcmp(type, "tree")) {
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entry->type = OBJ_TREE;
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} else if (!strcmp(type, "blob")) {
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entry->type = OBJ_BLOB;
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} else
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die("unable to pack object %s of type %s", sha1_to_hex(entry->sha1), type);
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}
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static void get_object_details(void)
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{
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int i;
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struct object_entry *entry = objects;
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for (i = 0; i < nr_objects; i++)
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check_object(entry++);
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}
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typedef int (*entry_sort_t)(const struct object_entry *, const struct object_entry *);
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static entry_sort_t current_sort;
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static int sort_comparator(const void *_a, const void *_b)
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{
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struct object_entry *a = *(struct object_entry **)_a;
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struct object_entry *b = *(struct object_entry **)_b;
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return current_sort(a,b);
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}
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static struct object_entry **create_sorted_list(entry_sort_t sort)
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{
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struct object_entry **list = xmalloc(nr_objects * sizeof(struct object_entry *));
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int i;
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for (i = 0; i < nr_objects; i++)
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list[i] = objects + i;
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current_sort = sort;
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qsort(list, nr_objects, sizeof(struct object_entry *), sort_comparator);
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return list;
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}
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static int sha1_sort(const struct object_entry *a, const struct object_entry *b)
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{
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return memcmp(a->sha1, b->sha1, 20);
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}
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static int type_size_sort(const struct object_entry *a, const struct object_entry *b)
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{
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if (a->type < b->type)
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return -1;
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if (a->type > b->type)
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return 1;
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if (a->size < b->size)
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return -1;
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if (a->size > b->size)
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return 1;
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return a < b ? -1 : (a > b);
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}
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struct unpacked {
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struct object_entry *entry;
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void *data;
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};
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/*
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* We search for deltas in a list sorted by type and by size, and
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* walk the "old" chain backwards in the list, so if the type
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* has changed or the size difference is too big, there's no point
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* in even continuing the walk, since the other old objects are
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* going to be even smaller or of a different type. So return -1
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* once we determine that there's no point even trying.
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*/
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static int try_delta(struct unpacked *cur, struct unpacked *old, unsigned max_depth)
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{
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struct object_entry *cur_entry = cur->entry;
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struct object_entry *old_entry = old->entry;
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unsigned long size, oldsize, delta_size;
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long max_size;
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void *delta_buf;
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/* Don't bother doing diffs between different types */
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if (cur_entry->type != old_entry->type)
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return -1;
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/* Size is guaranteed to be larger than or equal to oldsize */
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size = cur_entry->size;
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if (size < 50)
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return -1;
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oldsize = old_entry->size;
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if (size - oldsize > oldsize / 4)
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return -1;
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if (old_entry->depth >= max_depth)
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return 0;
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/*
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* NOTE!
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*
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* We always delta from the bigger to the smaller, since that's
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* more space-efficient (deletes don't have to say _what_ they
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* delete).
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*/
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max_size = size / 2 - 20;
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if (cur_entry->delta)
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max_size = cur_entry->delta_size-1;
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delta_buf = diff_delta(old->data, oldsize,
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cur->data, size, &delta_size, max_size);
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if (!delta_buf)
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return 0;
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cur_entry->delta = old_entry;
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cur_entry->delta_size = delta_size;
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cur_entry->depth = old_entry->depth + 1;
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free(delta_buf);
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return 0;
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}
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static void find_deltas(struct object_entry **list, int window, int depth)
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{
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unsigned int i;
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unsigned int array_size = window * sizeof(struct unpacked);
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struct unpacked *array = xmalloc(array_size);
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memset(array, 0, array_size);
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for (i = 0; i < nr_objects; i++) {
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unsigned int idx = i % window;
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struct object_entry *entry = list[i];
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struct unpacked *n = array + idx;
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unsigned long size;
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char type[10];
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int j;
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free(n->data);
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n->entry = entry;
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n->data = read_sha1_file(entry->sha1, type, &size);
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if (size != entry->size)
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die("object %s inconsistent object length (%lu vs %lu)", sha1_to_hex(entry->sha1), size, entry->size);
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j = window;
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while (--j > 0) {
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unsigned int other_idx = idx + j;
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struct unpacked *m;
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if (other_idx >= window)
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other_idx -= window;
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m = array + other_idx;
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if (!m->entry)
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break;
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if (try_delta(n, m, depth) < 0)
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break;
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}
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}
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}
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int main(int argc, char **argv)
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{
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char line[128];
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int window = 10, depth = 10;
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int i;
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for (i = 1; i < argc; i++) {
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const char *arg = argv[i];
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if (*arg == '-') {
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if (!strncmp("--window=", arg, 9)) {
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char *end;
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window = strtoul(arg+9, &end, 0);
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if (!arg[9] || *end)
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usage(pack_usage);
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continue;
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}
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if (!strncmp("--depth=", arg, 8)) {
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char *end;
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depth = strtoul(arg+8, &end, 0);
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if (!arg[8] || *end)
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usage(pack_usage);
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continue;
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}
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usage(pack_usage);
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}
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if (base_name)
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usage(pack_usage);
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base_name = arg;
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}
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if (!base_name)
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usage(pack_usage);
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while (fgets(line, sizeof(line), stdin) != NULL) {
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unsigned char sha1[20];
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if (get_sha1_hex(line, sha1))
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die("expected sha1, got garbage");
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add_object_entry(sha1);
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}
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get_object_details();
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printf("Packing %d objects\n", nr_objects);
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sorted_by_sha = create_sorted_list(sha1_sort);
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sorted_by_type = create_sorted_list(type_size_sort);
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if (window && depth)
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find_deltas(sorted_by_type, window+1, depth);
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write_pack_file();
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write_index_file();
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return 0;
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}
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