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![Nicolas Pitre](/assets/img/avatar_default.png)
After experimenting with code to add the ability to encode a delta against part of the deltified file, it turns out that resulting packs are _bigger_ than when this ability is not used. The raw delta output might be smaller, but it doesn't compress as well using gzip with a negative net saving on average. Said bit would in fact be more useful to allow for encoding the copying of chunks larger than 64KB providing more savings with large files. This will correspond to packs version 3. While the current code still produces packs version 2, it is made future proof so pack versions 2 and 3 are accepted. Any pack version 2 are compatible with version 3 since the redefined bit was never used before. When enough time has passed, code to use that bit to produce version 3 packs could be added. Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Junio C Hamano <junkio@cox.net>
313 lines
6.6 KiB
C
313 lines
6.6 KiB
C
#include "cache.h"
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#include "object.h"
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#include "delta.h"
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#include "pack.h"
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#include <sys/time.h>
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static int dry_run, quiet;
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static const char unpack_usage[] = "git-unpack-objects [-n] [-q] < pack-file";
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/* We always read in 4kB chunks. */
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static unsigned char buffer[4096];
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static unsigned long offset, len, eof;
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static SHA_CTX ctx;
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/*
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* Make sure at least "min" bytes are available in the buffer, and
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* return the pointer to the buffer.
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*/
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static void * fill(int min)
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{
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if (min <= len)
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return buffer + offset;
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if (eof)
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die("unable to fill input");
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if (min > sizeof(buffer))
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die("cannot fill %d bytes", min);
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if (offset) {
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SHA1_Update(&ctx, buffer, offset);
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memcpy(buffer, buffer + offset, len);
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offset = 0;
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}
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do {
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int ret = xread(0, buffer + len, sizeof(buffer) - len);
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if (ret <= 0) {
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if (!ret)
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die("early EOF");
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die("read error on input: %s", strerror(errno));
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}
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len += ret;
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} while (len < min);
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return buffer;
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}
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static void use(int bytes)
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{
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if (bytes > len)
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die("used more bytes than were available");
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len -= bytes;
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offset += bytes;
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}
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static void *get_data(unsigned long size)
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{
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z_stream stream;
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void *buf = xmalloc(size);
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memset(&stream, 0, sizeof(stream));
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stream.next_out = buf;
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stream.avail_out = size;
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stream.next_in = fill(1);
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stream.avail_in = len;
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inflateInit(&stream);
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for (;;) {
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int ret = inflate(&stream, 0);
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use(len - stream.avail_in);
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if (stream.total_out == size && ret == Z_STREAM_END)
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break;
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if (ret != Z_OK)
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die("inflate returned %d\n", ret);
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stream.next_in = fill(1);
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stream.avail_in = len;
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}
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inflateEnd(&stream);
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return buf;
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}
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struct delta_info {
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unsigned char base_sha1[20];
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unsigned long size;
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void *delta;
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struct delta_info *next;
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};
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static struct delta_info *delta_list;
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static void add_delta_to_list(unsigned char *base_sha1, void *delta, unsigned long size)
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{
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struct delta_info *info = xmalloc(sizeof(*info));
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memcpy(info->base_sha1, base_sha1, 20);
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info->size = size;
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info->delta = delta;
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info->next = delta_list;
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delta_list = info;
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}
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static void added_object(unsigned char *sha1, const char *type, void *data, unsigned long size);
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static void write_object(void *buf, unsigned long size, const char *type)
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{
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unsigned char sha1[20];
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if (write_sha1_file(buf, size, type, sha1) < 0)
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die("failed to write object");
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added_object(sha1, type, buf, size);
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}
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static int resolve_delta(const char *type,
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void *base, unsigned long base_size,
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void *delta, unsigned long delta_size)
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{
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void *result;
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unsigned long result_size;
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result = patch_delta(base, base_size,
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delta, delta_size,
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&result_size);
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if (!result)
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die("failed to apply delta");
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free(delta);
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write_object(result, result_size, type);
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free(result);
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return 0;
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}
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static void added_object(unsigned char *sha1, const char *type, void *data, unsigned long size)
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{
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struct delta_info **p = &delta_list;
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struct delta_info *info;
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while ((info = *p) != NULL) {
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if (!memcmp(info->base_sha1, sha1, 20)) {
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*p = info->next;
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p = &delta_list;
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resolve_delta(type, data, size, info->delta, info->size);
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free(info);
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continue;
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}
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p = &info->next;
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}
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}
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static int unpack_non_delta_entry(enum object_type kind, unsigned long size)
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{
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void *buf = get_data(size);
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const char *type;
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switch (kind) {
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case OBJ_COMMIT: type = "commit"; break;
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case OBJ_TREE: type = "tree"; break;
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case OBJ_BLOB: type = "blob"; break;
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case OBJ_TAG: type = "tag"; break;
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default: die("bad type %d", kind);
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}
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if (!dry_run)
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write_object(buf, size, type);
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free(buf);
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return 0;
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}
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static int unpack_delta_entry(unsigned long delta_size)
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{
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void *delta_data, *base;
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unsigned long base_size;
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char type[20];
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unsigned char base_sha1[20];
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int result;
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memcpy(base_sha1, fill(20), 20);
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use(20);
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delta_data = get_data(delta_size);
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if (dry_run) {
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free(delta_data);
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return 0;
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}
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if (!has_sha1_file(base_sha1)) {
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add_delta_to_list(base_sha1, delta_data, delta_size);
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return 0;
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}
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base = read_sha1_file(base_sha1, type, &base_size);
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if (!base)
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die("failed to read delta-pack base object %s", sha1_to_hex(base_sha1));
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result = resolve_delta(type, base, base_size, delta_data, delta_size);
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free(base);
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return result;
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}
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static void unpack_one(unsigned nr, unsigned total)
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{
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unsigned shift;
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unsigned char *pack, c;
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unsigned long size;
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enum object_type type;
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pack = fill(1);
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c = *pack;
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use(1);
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type = (c >> 4) & 7;
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size = (c & 15);
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shift = 4;
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while (c & 0x80) {
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pack = fill(1);
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c = *pack++;
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use(1);
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size += (c & 0x7f) << shift;
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shift += 7;
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}
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if (!quiet) {
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static unsigned long last_sec;
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static unsigned last_percent;
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struct timeval now;
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unsigned percentage = (nr * 100) / total;
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gettimeofday(&now, NULL);
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if (percentage != last_percent || now.tv_sec != last_sec) {
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last_sec = now.tv_sec;
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last_percent = percentage;
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fprintf(stderr, "%4u%% (%u/%u) done\r", percentage, nr, total);
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}
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}
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switch (type) {
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case OBJ_COMMIT:
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case OBJ_TREE:
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case OBJ_BLOB:
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case OBJ_TAG:
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unpack_non_delta_entry(type, size);
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return;
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case OBJ_DELTA:
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unpack_delta_entry(size);
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return;
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default:
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die("bad object type %d", type);
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}
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}
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/*
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* We unpack from the end, older files first. Now, usually
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* there are deltas etc, so we'll not actually write the
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* objects in that order, but we might as well try..
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*/
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static void unpack_all(void)
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{
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int i;
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struct pack_header *hdr = fill(sizeof(struct pack_header));
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unsigned nr_objects = ntohl(hdr->hdr_entries);
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if (ntohl(hdr->hdr_signature) != PACK_SIGNATURE)
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die("bad pack file");
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if (!pack_version_ok(hdr->hdr_version))
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die("unknown pack file version %d", ntohl(hdr->hdr_version));
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fprintf(stderr, "Unpacking %d objects\n", nr_objects);
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use(sizeof(struct pack_header));
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for (i = 0; i < nr_objects; i++)
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unpack_one(i+1, nr_objects);
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if (delta_list)
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die("unresolved deltas left after unpacking");
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}
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int main(int argc, char **argv)
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{
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int i;
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unsigned char sha1[20];
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setup_git_directory();
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quiet = !isatty(2);
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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 (!strcmp(arg, "-n")) {
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dry_run = 1;
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continue;
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}
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if (!strcmp(arg, "-q")) {
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quiet = 1;
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continue;
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}
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usage(unpack_usage);
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}
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/* We don't take any non-flag arguments now.. Maybe some day */
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usage(unpack_usage);
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}
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SHA1_Init(&ctx);
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unpack_all();
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SHA1_Update(&ctx, buffer, offset);
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SHA1_Final(sha1, &ctx);
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if (memcmp(fill(20), sha1, 20))
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die("final sha1 did not match");
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use(20);
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/* Write the last part of the buffer to stdout */
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while (len) {
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int ret = xwrite(1, buffer + offset, len);
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if (ret <= 0)
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break;
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len -= ret;
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offset += ret;
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}
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/* All done */
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if (!quiet)
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fprintf(stderr, "\n");
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return 0;
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}
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