#include "cache.h"
#include "pack-revindex.h"
+#include "object-store.h"
/*
* Pack index for existing packs give us easy access to the offsets into
* 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
+ * The pack index file is sorted by object name mapping to offset;
+ * this 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)
+/*
+ * 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)
{
- 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;
+ /*
+ * 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, *from, *to;
+ int bits;
+ unsigned *pos;
+
+ ALLOC_ARRAY(pos, BUCKETS);
+ ALLOC_ARRAY(tmp, n);
+ from = entries;
+ to = tmp;
+
+ /*
+ * 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) {
+ 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, to);
}
- /* revindex elements are lazily initialized */
-}
-static int cmp_offset(const void *a_, const void *b_)
-{
- const struct revindex_entry *a = a_;
- const struct revindex_entry *b = b_;
- return (a->offset < b->offset) ? -1 : (a->offset > b->offset) ? 1 : 0;
+ /*
+ * 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)
+ COPY_ARRAY(entries, tmp, n);
+ 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)
+static void create_pack_revindex(struct packed_git *p)
{
- struct packed_git *p = rix->p;
- int num_ent = p->num_objects;
- int i;
+ unsigned num_ent = p->num_objects;
+ unsigned i;
const char *index = p->index_data;
- rix->revindex = xmalloc(sizeof(*rix->revindex) * (num_ent + 1));
+ ALLOC_ARRAY(p->revindex, num_ent + 1);
index += 4 * 256;
if (p->index_version > 1) {
for (i = 0; i < num_ent; i++) {
uint32_t off = ntohl(*off_32++);
if (!(off & 0x80000000)) {
- rix->revindex[i].offset = off;
+ p->revindex[i].offset = off;
} else {
- rix->revindex[i].offset =
- ((uint64_t)ntohl(*off_64++)) << 32;
- rix->revindex[i].offset |=
- ntohl(*off_64++);
+ p->revindex[i].offset = get_be64(off_64);
+ off_64 += 2;
}
- rix->revindex[i].nr = i;
+ p->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;
+ p->revindex[i].offset = ntohl(hl);
+ p->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;
- qsort(rix->revindex, num_ent, sizeof(*rix->revindex), cmp_offset);
+ p->revindex[num_ent].offset = p->pack_size - 20;
+ p->revindex[num_ent].nr = -1;
+ sort_revindex(p->revindex, num_ent, p->pack_size);
}
-struct revindex_entry *find_pack_revindex(struct packed_git *p, off_t ofs)
+void load_pack_revindex(struct packed_git *p)
{
- int num;
- int 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;
+ if (!p->revindex)
+ create_pack_revindex(p);
+}
+
+int find_revindex_position(struct packed_git *p, off_t ofs)
+{
+ int lo = 0;
+ int hi = p->num_objects + 1;
+ struct revindex_entry *revindex = p->revindex;
+
do {
- int mi = (lo + hi) / 2;
+ unsigned mi = lo + (hi - lo) / 2;
if (revindex[mi].offset == ofs) {
- return revindex + mi;
+ return mi;
} else if (ofs < revindex[mi].offset)
hi = mi;
else
lo = mi + 1;
} while (lo < hi);
+
error("bad offset for revindex");
- return NULL;
+ return -1;
}
-void discard_revindex(void)
+struct revindex_entry *find_pack_revindex(struct packed_git *p, off_t ofs)
{
- 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;
- }
+ int pos;
+
+ load_pack_revindex(p);
+ pos = find_revindex_position(p, ofs);
+
+ if (pos < 0)
+ return NULL;
+
+ return p->revindex + pos;
}
projects / platform / upstream / git.git / blobdiff