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Change pack file format. Hopefully for the last time.

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This also adds a header with a signature, version info, and the number
of objects to the pack file.  It also encodes the file length and type
more efficiently.
This commit is contained in:
Linus Torvalds
2005-06-28 14:21:02 -07:00
parent d22b9290ab
commit a733cb606f
4 changed files with 175 additions and 74 deletions
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84
pack-objects.c
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@ -2,25 +2,18 @@
#include "cache.h"
#include "object.h"
#include "delta.h"
#include "pack.h"
#include "csum-file.h"
static const char pack_usage[] = "git-pack-objects [--window=N] [--depth=N] {--stdout | base-name} < object-list";
/*
* The object type is a single-character shorthand:
* - 'C' for "Commit"
* - 'T' for "Tree"
* - 'B' for "Blob"
* - 'G' for "taG"
* - 'D' for "Delta"
*/
struct object_entry {
unsigned char sha1[20];
unsigned long size;
unsigned long offset;
unsigned int depth;
unsigned int hash;
unsigned char type;
enum object_type type;
unsigned long delta_size;
struct object_entry *delta;
};
@ -49,13 +42,54 @@ static void *delta_against(void *buf, unsigned long size, struct object_entry *e
return delta_buf;
}
/*
* The per-object header is a pretty dense thing, which is
* - first byte: low four bits are "size", then three bits of "type",
* and the high bit is "size continues".
* - each byte afterwards: low seven bits are size continuation,
* with the high bit being "size continues"
*/
static int encode_header(enum object_type type, unsigned long size, unsigned char *hdr)
{
int n = 1, i;
unsigned char c;
if (type < OBJ_COMMIT || type > OBJ_DELTA)
die("bad type %d", type);
/*
* Shift the size up by 7 bits at a time,
* until you get bits in the "high four".
* That will be our beginning. We'll have
* four size bits in 28..31, then groups
* of seven in 21..27, 14..20, 7..13 and
* finally 0..6.
*/
if (size) {
n = 5;
while (!(size & 0xfe000000)) {
size <<= 7;
n--;
}
}
c = (type << 4) | (size >> 28);
for (i = 1; i < n; i++) {
*hdr++ = c | 0x80;
c = (size >> 21) & 0x7f;
size <<= 7;
}
*hdr = c;
return n;
}
static unsigned long write_object(struct sha1file *f, struct object_entry *entry)
{
unsigned long size;
char type[10];
void *buf = read_sha1_file(entry->sha1, type, &size);
char header[25];
unsigned char header[10];
unsigned hdrlen, datalen;
enum object_type obj_type;
if (!buf)
die("unable to read %s", sha1_to_hex(entry->sha1));
@ -67,18 +101,18 @@ static unsigned long write_object(struct sha1file *f, struct object_entry *entry
* length, except for deltas that has the 20 bytes of delta sha
* instead.
*/
header[0] = entry->type;
hdrlen = 5;
obj_type = entry->type;
if (entry->delta) {
header[0] = 'D';
memcpy(header+5, entry->delta, 20);
buf = delta_against(buf, size, entry);
size = entry->delta_size;
hdrlen = 25;
obj_type = OBJ_DELTA;
}
datalen = htonl(size);
memcpy(header+1, &datalen, 4);
hdrlen = encode_header(obj_type, size, header);
sha1write(f, header, hdrlen);
if (entry->delta) {
sha1write(f, entry->delta, 20);
hdrlen += 20;
}
datalen = sha1write_compressed(f, buf, size);
free(buf);
return hdrlen + datalen;
@ -88,13 +122,19 @@ static void write_pack_file(void)
{
int i;
struct sha1file *f;
unsigned long offset = 0;
unsigned long offset;
unsigned long mb;
struct pack_header hdr;
if (!base_name)
f = sha1fd(1, "<stdout>");
else
f = sha1create("%s.%s", base_name, "pack");
hdr.hdr_signature = htonl(PACK_SIGNATURE);
hdr.hdr_version = htonl(1);
hdr.hdr_entries = htonl(nr_objects);
sha1write(f, &hdr, sizeof(hdr));
offset = sizeof(hdr);
for (i = 0; i < nr_objects; i++) {
struct object_entry *entry = objects + i;
entry->offset = offset;
@ -168,13 +208,13 @@ static void check_object(struct object_entry *entry)
if (!sha1_object_info(entry->sha1, type, &entry->size)) {
if (!strcmp(type, "commit")) {
entry->type = 'C';
entry->type = OBJ_COMMIT;
} else if (!strcmp(type, "tree")) {
entry->type = 'T';
entry->type = OBJ_TREE;
} else if (!strcmp(type, "blob")) {
entry->type = 'B';
entry->type = OBJ_BLOB;
} else if (!strcmp(type, "tag")) {
entry->type = 'G';
entry->type = OBJ_TAG;
} else
die("unable to pack object %s of type %s",
sha1_to_hex(entry->sha1), type);