[thirdparty/git.git] / pack-revindex.c

#include "cache.h"
#include "pack-revindex.h"

/*
 * Pack index for existing packs give us easy access to the offsets into
 * corresponding pack file where each object's data starts, but the entries
 * do not store the size of the compressed representation (uncompressed
 * size is easily available by examining the pack entry header).  It is
 * also rather expensive to find the sha1 for an object given its offset.
 *
 * We build a hashtable of existing packs (pack_revindex), and keep reverse
 * index here -- pack index file is sorted by object name mapping to offset;
 * this pack_revindex[].revindex array is a list of offset/index_nr pairs
 * ordered by offset, so if you know the offset of an object, next offset
 * is where its packed representation ends and the index_nr can be used to
 * get the object sha1 from the main index.
 */

struct pack_revindex {
	struct packed_git *p;
	struct revindex_entry *revindex;
};

static struct pack_revindex *pack_revindex;
static int pack_revindex_hashsz;

static int pack_revindex_ix(struct packed_git *p)
{
	unsigned long ui = (unsigned long)p;
	int i;

	ui = ui ^ (ui >> 16); /* defeat structure alignment */
	i = (int)(ui % pack_revindex_hashsz);
	while (pack_revindex[i].p) {
		if (pack_revindex[i].p == p)
			return i;
		if (++i == pack_revindex_hashsz)
			i = 0;
	}
	return -1 - i;
}

static void init_pack_revindex(void)
{
	int num;
	struct packed_git *p;

	for (num = 0, p = packed_git; p; p = p->next)
		num++;
	if (!num)
		return;
	pack_revindex_hashsz = num * 11;
	pack_revindex = xcalloc(sizeof(*pack_revindex), pack_revindex_hashsz);
	for (p = packed_git; p; p = p->next) {
		num = pack_revindex_ix(p);
		num = - 1 - num;
		pack_revindex[num].p = p;
	}
	/* revindex elements are lazily initialized */
}

/*
 * This is a least-significant-digit radix sort.
 *
 * It sorts each of the "n" items in "entries" by its offset field. The "max"
 * parameter must be at least as large as the largest offset in the array,
 * and lets us quit the sort early.
 */
static void sort_revindex(struct revindex_entry *entries, unsigned n, off_t max)
{
	/*
	 * We use a "digit" size of 16 bits. That keeps our memory
	 * usage reasonable, and we can generally (for a 4G or smaller
	 * packfile) quit after two rounds of radix-sorting.
	 */
#define DIGIT_SIZE (16)
#define BUCKETS (1 << DIGIT_SIZE)
	/*
	 * We want to know the bucket that a[i] will go into when we are using
	 * the digit that is N bits from the (least significant) end.
	 */
#define BUCKET_FOR(a, i, bits) (((a)[(i)].offset >> (bits)) & (BUCKETS-1))

	/*
	 * We need O(n) temporary storage. Rather than do an extra copy of the
	 * partial results into "entries", we sort back and forth between the
	 * real array and temporary storage. In each iteration of the loop, we
	 * keep track of them with alias pointers, always sorting from "from"
	 * to "to".
	 */
	struct revindex_entry *tmp = xmalloc(n * sizeof(*tmp));
	struct revindex_entry *from = entries, *to = tmp;
	int bits;
	unsigned *pos = xmalloc(BUCKETS * sizeof(*pos));

	/*
	 * If (max >> bits) is zero, then we know that the radix digit we are
	 * on (and any higher) will be zero for all entries, and our loop will
	 * be a no-op, as everybody lands in the same zero-th bucket.
	 */
	for (bits = 0; max >> bits; bits += DIGIT_SIZE) {
		struct revindex_entry *swap;
		unsigned i;

		memset(pos, 0, BUCKETS * sizeof(*pos));

		/*
		 * We want pos[i] to store the index of the last element that
		 * will go in bucket "i" (actually one past the last element).
		 * To do this, we first count the items that will go in each
		 * bucket, which gives us a relative offset from the last
		 * bucket. We can then cumulatively add the index from the
		 * previous bucket to get the true index.
		 */
		for (i = 0; i < n; i++)
			pos[BUCKET_FOR(from, i, bits)]++;
		for (i = 1; i < BUCKETS; i++)
			pos[i] += pos[i-1];

		/*
		 * Now we can drop the elements into their correct buckets (in
		 * our temporary array).  We iterate the pos counter backwards
		 * to avoid using an extra index to count up. And since we are
		 * going backwards there, we must also go backwards through the
		 * array itself, to keep the sort stable.
		 *
		 * Note that we use an unsigned iterator to make sure we can
		 * handle 2^32-1 objects, even on a 32-bit system. But this
		 * means we cannot use the more obvious "i >= 0" loop condition
		 * for counting backwards, and must instead check for
		 * wrap-around with UINT_MAX.
		 */
		for (i = n - 1; i != UINT_MAX; i--)
			to[--pos[BUCKET_FOR(from, i, bits)]] = from[i];

		/*
		 * Now "to" contains the most sorted list, so we swap "from" and
		 * "to" for the next iteration.
		 */
		swap = from;
		from = to;
		to = swap;
	}

	/*
	 * If we ended with our data in the original array, great. If not,
	 * we have to move it back from the temporary storage.
	 */
	if (from != entries)
		memcpy(entries, tmp, n * sizeof(*entries));
	free(tmp);
	free(pos);

#undef BUCKET_FOR
#undef BUCKETS
#undef DIGIT_SIZE
}

/*
 * Ordered list of offsets of objects in the pack.
 */
static void create_pack_revindex(struct pack_revindex *rix)
{
	struct packed_git *p = rix->p;
	unsigned num_ent = p->num_objects;
	unsigned i;
	const char *index = p->index_data;

	rix->revindex = xmalloc(sizeof(*rix->revindex) * (num_ent + 1));
	index += 4 * 256;

	if (p->index_version > 1) {
		const uint32_t *off_32 =
			(uint32_t *)(index + 8 + p->num_objects * (20 + 4));
		const uint32_t *off_64 = off_32 + p->num_objects;
		for (i = 0; i < num_ent; i++) {
			uint32_t off = ntohl(*off_32++);
			if (!(off & 0x80000000)) {
				rix->revindex[i].offset = off;
			} else {
				rix->revindex[i].offset =
					((uint64_t)ntohl(*off_64++)) << 32;
				rix->revindex[i].offset |=
					ntohl(*off_64++);
			}
			rix->revindex[i].nr = i;
		}
	} else {
		for (i = 0; i < num_ent; i++) {
			uint32_t hl = *((uint32_t *)(index + 24 * i));
			rix->revindex[i].offset = ntohl(hl);
			rix->revindex[i].nr = i;
		}
	}

	/* This knows the pack format -- the 20-byte trailer
	 * follows immediately after the last object data.
	 */
	rix->revindex[num_ent].offset = p->pack_size - 20;
	rix->revindex[num_ent].nr = -1;
	sort_revindex(rix->revindex, num_ent, p->pack_size);
}

struct revindex_entry *find_pack_revindex(struct packed_git *p, off_t ofs)
{
	int num;
	unsigned lo, hi;
	struct pack_revindex *rix;
	struct revindex_entry *revindex;

	if (!pack_revindex_hashsz)
		init_pack_revindex();
	num = pack_revindex_ix(p);
	if (num < 0)
		die("internal error: pack revindex fubar");

	rix = &pack_revindex[num];
	if (!rix->revindex)
		create_pack_revindex(rix);
	revindex = rix->revindex;

	lo = 0;
	hi = p->num_objects + 1;
	do {
		unsigned mi = lo + (hi - lo) / 2;
		if (revindex[mi].offset == ofs) {
			return revindex + mi;
		} else if (ofs < revindex[mi].offset)
			hi = mi;
		else
			lo = mi + 1;
	} while (lo < hi);
	error("bad offset for revindex");
	return NULL;
}

void discard_revindex(void)
{
	if (pack_revindex_hashsz) {
		int i;
		for (i = 0; i < pack_revindex_hashsz; i++)
			free(pack_revindex[i].revindex);
		free(pack_revindex);
		pack_revindex_hashsz = 0;
	}
}
Commit	Line	Data
3449f8c4 NP	1	#include "cache.h"
	2	#include "pack-revindex.h"
	3
	4	/*
	5	* Pack index for existing packs give us easy access to the offsets into
	6	* corresponding pack file where each object's data starts, but the entries
	7	* do not store the size of the compressed representation (uncompressed
	8	* size is easily available by examining the pack entry header). It is
	9	* also rather expensive to find the sha1 for an object given its offset.
	10	*
	11	* We build a hashtable of existing packs (pack_revindex), and keep reverse
	12	* index here -- pack index file is sorted by object name mapping to offset;
	13	* this pack_revindex[].revindex array is a list of offset/index_nr pairs
	14	* ordered by offset, so if you know the offset of an object, next offset
	15	* is where its packed representation ends and the index_nr can be used to
	16	* get the object sha1 from the main index.
	17	*/
	18
	19	struct pack_revindex {
	20	struct packed_git *p;
	21	struct revindex_entry *revindex;
	22	};
	23
	24	static struct pack_revindex *pack_revindex;
	25	static int pack_revindex_hashsz;
	26
	27	static int pack_revindex_ix(struct packed_git *p)
	28	{
	29	unsigned long ui = (unsigned long)p;
	30	int i;
	31
	32	ui = ui ^ (ui >> 16); /* defeat structure alignment */
	33	i = (int)(ui % pack_revindex_hashsz);
	34	while (pack_revindex[i].p) {
	35	if (pack_revindex[i].p == p)
	36	return i;
	37	if (++i == pack_revindex_hashsz)
	38	i = 0;
	39	}
	40	return -1 - i;
	41	}
	42
1f5c74f6	43	static void init_pack_revindex(void)
3449f8c4 NP	44	{
	45	int num;
	46	struct packed_git *p;
	47
	48	for (num = 0, p = packed_git; p; p = p->next)
	49	num++;
	50	if (!num)
	51	return;
	52	pack_revindex_hashsz = num * 11;
	53	pack_revindex = xcalloc(sizeof(*pack_revindex), pack_revindex_hashsz);
	54	for (p = packed_git; p; p = p->next) {
	55	num = pack_revindex_ix(p);
	56	num = - 1 - num;
	57	pack_revindex[num].p = p;
	58	}
	59	/* revindex elements are lazily initialized */
	60	}
	61
8b8dfd51 JK	62	/*
	63	* This is a least-significant-digit radix sort.
	64	*
	65	* It sorts each of the "n" items in "entries" by its offset field. The "max"
	66	* parameter must be at least as large as the largest offset in the array,
	67	* and lets us quit the sort early.
	68	*/
	69	static void sort_revindex(struct revindex_entry *entries, unsigned n, off_t max)
3449f8c4	70	{
8b8dfd51 JK	71	/*
	72	* We use a "digit" size of 16 bits. That keeps our memory
	73	* usage reasonable, and we can generally (for a 4G or smaller
	74	* packfile) quit after two rounds of radix-sorting.
	75	*/
	76	#define DIGIT_SIZE (16)
	77	#define BUCKETS (1 << DIGIT_SIZE)
	78	/*
	79	* We want to know the bucket that a[i] will go into when we are using
	80	* the digit that is N bits from the (least significant) end.
	81	*/
	82	#define BUCKET_FOR(a, i, bits) (((a)[(i)].offset >> (bits)) & (BUCKETS-1))
	83
	84	/*
	85	* We need O(n) temporary storage. Rather than do an extra copy of the
	86	* partial results into "entries", we sort back and forth between the
	87	* real array and temporary storage. In each iteration of the loop, we
	88	* keep track of them with alias pointers, always sorting from "from"
	89	* to "to".
	90	*/
	91	struct revindex_entry tmp = xmalloc(n sizeof(*tmp));
	92	struct revindex_entry from = entries, to = tmp;
	93	int bits;
	94	unsigned pos = xmalloc(BUCKETS sizeof(*pos));
	95
	96	/*
	97	* If (max >> bits) is zero, then we know that the radix digit we are
	98	* on (and any higher) will be zero for all entries, and our loop will
	99	* be a no-op, as everybody lands in the same zero-th bucket.
	100	*/
	101	for (bits = 0; max >> bits; bits += DIGIT_SIZE) {
	102	struct revindex_entry *swap;
	103	unsigned i;
	104
	105	memset(pos, 0, BUCKETS * sizeof(*pos));
	106
	107	/*
	108	* We want pos[i] to store the index of the last element that
	109	* will go in bucket "i" (actually one past the last element).
	110	* To do this, we first count the items that will go in each
	111	* bucket, which gives us a relative offset from the last
	112	* bucket. We can then cumulatively add the index from the
	113	* previous bucket to get the true index.
	114	*/
	115	for (i = 0; i < n; i++)
	116	pos[BUCKET_FOR(from, i, bits)]++;
	117	for (i = 1; i < BUCKETS; i++)
	118	pos[i] += pos[i-1];
	119
	120	/*
	121	* Now we can drop the elements into their correct buckets (in
	122	* our temporary array). We iterate the pos counter backwards
	123	* to avoid using an extra index to count up. And since we are
	124	* going backwards there, we must also go backwards through the
	125	* array itself, to keep the sort stable.
	126	*
	127	* Note that we use an unsigned iterator to make sure we can
	128	* handle 2^32-1 objects, even on a 32-bit system. But this
	129	* means we cannot use the more obvious "i >= 0" loop condition
	130	* for counting backwards, and must instead check for
	131	* wrap-around with UINT_MAX.
	132	*/
	133	for (i = n - 1; i != UINT_MAX; i--)
	134	to[--pos[BUCKET_FOR(from, i, bits)]] = from[i];
135
136	/*
137	* Now "to" contains the most sorted list, so we swap "from" and
138	* "to" for the next iteration.
139	*/
140	swap = from;
141	from = to;
142	to = swap;
143	}
144
145	/*
146	* If we ended with our data in the original array, great. If not,
147	* we have to move it back from the temporary storage.
148	*/
149	if (from != entries)
150	memcpy(entries, tmp, n * sizeof(*entries));
151	free(tmp);
152	free(pos);
153
154	#undef BUCKET_FOR
155	#undef BUCKETS
156	#undef DIGIT_SIZE
3449f8c4 NP	157	}
	158
	159	/*
	160	* Ordered list of offsets of objects in the pack.
	161	*/
	162	static void create_pack_revindex(struct pack_revindex *rix)
	163	{
	164	struct packed_git *p = rix->p;
012b32bb JK	165	unsigned num_ent = p->num_objects;
012b32bb JK	166	unsigned i;
3449f8c4 NP	167	const char *index = p->index_data;
	168
	169	rix->revindex = xmalloc(sizeof(rix->revindex) (num_ent + 1));
	170	index += 4 * 256;
	171
	172	if (p->index_version > 1) {
	173	const uint32_t *off_32 =
	174	(uint32_t )(index + 8 + p->num_objects (20 + 4));
	175	const uint32_t *off_64 = off_32 + p->num_objects;
	176	for (i = 0; i < num_ent; i++) {
	177	uint32_t off = ntohl(*off_32++);
	178	if (!(off & 0x80000000)) {
	179	rix->revindex[i].offset = off;
	180	} else {
	181	rix->revindex[i].offset =
	182	((uint64_t)ntohl(*off_64++)) << 32;
	183	rix->revindex[i].offset \|=
	184	ntohl(*off_64++);
	185	}
	186	rix->revindex[i].nr = i;
	187	}
	188	} else {
	189	for (i = 0; i < num_ent; i++) {
	190	uint32_t hl = ((uint32_t )(index + 24 * i));
	191	rix->revindex[i].offset = ntohl(hl);
	192	rix->revindex[i].nr = i;
	193	}
	194	}
	195
	196	/* This knows the pack format -- the 20-byte trailer
	197	* follows immediately after the last object data.
	198	*/
	199	rix->revindex[num_ent].offset = p->pack_size - 20;
	200	rix->revindex[num_ent].nr = -1;
8b8dfd51	201	sort_revindex(rix->revindex, num_ent, p->pack_size);
3449f8c4 NP	202	}
	203
	204	struct revindex_entry find_pack_revindex(struct packed_git p, off_t ofs)
	205	{
	206	int num;
012b32bb	207	unsigned lo, hi;
3449f8c4 NP	208	struct pack_revindex *rix;
	209	struct revindex_entry *revindex;
	210
1f5c74f6 NP	211	if (!pack_revindex_hashsz)
1f5c74f6 NP	212	init_pack_revindex();
3449f8c4 NP	213	num = pack_revindex_ix(p);
3449f8c4 NP	214	if (num < 0)
1f5c74f6	215	die("internal error: pack revindex fubar");
3449f8c4 NP	216
	217	rix = &pack_revindex[num];
	218	if (!rix->revindex)
	219	create_pack_revindex(rix);
	220	revindex = rix->revindex;
	221
	222	lo = 0;
	223	hi = p->num_objects + 1;
	224	do {
012b32bb	225	unsigned mi = lo + (hi - lo) / 2;
3449f8c4 NP	226	if (revindex[mi].offset == ofs) {
	227	return revindex + mi;
	228	} else if (ofs < revindex[mi].offset)
	229	hi = mi;
	230	else
	231	lo = mi + 1;
	232	} while (lo < hi);
08698b1e NP	233	error("bad offset for revindex");
08698b1e NP	234	return NULL;
3449f8c4	235	}
4b480c67 NP	236
	237	void discard_revindex(void)
	238	{
	239	if (pack_revindex_hashsz) {
	240	int i;
	241	for (i = 0; i < pack_revindex_hashsz; i++)
24deea52	242	free(pack_revindex[i].revindex);
4b480c67 NP	243	free(pack_revindex);
	244	pack_revindex_hashsz = 0;
	245	}
	246	}