/brz/remove-bazaar

/*

 * diff-delta.c: generate a delta between two buffers

 *

 * This code was greatly inspired by parts of LibXDiff from Davide Libenzi

 * http://www.xmailserver.org/xdiff-lib.html

 *

 * Rewritten for GIT by Nicolas Pitre <nico@cam.org>, (C) 2005-2007

 *

 * This code is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License version 2 as

 * published by the Free Software Foundation.

 */

#include "delta.h"

#include <assert.h>

/* maximum hash entry list for the same hash bucket */

#define HASH_LIMIT 64

#define RABIN_SHIFT 23

#define RABIN_WINDOW 16

static const unsigned int T[256] = {

	0x00000000, 0xab59b4d1, 0x56b369a2, 0xfdeadd73, 0x063f6795, 0xad66d344,

	0x508c0e37, 0xfbd5bae6, 0x0c7ecf2a, 0xa7277bfb, 0x5acda688, 0xf1941259,

	0x0a41a8bf, 0xa1181c6e, 0x5cf2c11d, 0xf7ab75cc, 0x18fd9e54, 0xb3a42a85,

	0x4e4ef7f6, 0xe5174327, 0x1ec2f9c1, 0xb59b4d10, 0x48719063, 0xe32824b2,

	0x1483517e, 0xbfdae5af, 0x423038dc, 0xe9698c0d, 0x12bc36eb, 0xb9e5823a,

	0x440f5f49, 0xef56eb98, 0x31fb3ca8, 0x9aa28879, 0x6748550a, 0xcc11e1db,

	0x37c45b3d, 0x9c9defec, 0x6177329f, 0xca2e864e, 0x3d85f382, 0x96dc4753,

	0x6b369a20, 0xc06f2ef1, 0x3bba9417, 0x90e320c6, 0x6d09fdb5, 0xc6504964,

	0x2906a2fc, 0x825f162d, 0x7fb5cb5e, 0xd4ec7f8f, 0x2f39c569, 0x846071b8,

	0x798aaccb, 0xd2d3181a, 0x25786dd6, 0x8e21d907, 0x73cb0474, 0xd892b0a5,

	0x23470a43, 0x881ebe92, 0x75f463e1, 0xdeadd730, 0x63f67950, 0xc8afcd81,

	0x354510f2, 0x9e1ca423, 0x65c91ec5, 0xce90aa14, 0x337a7767, 0x9823c3b6,

	0x6f88b67a, 0xc4d102ab, 0x393bdfd8, 0x92626b09, 0x69b7d1ef, 0xc2ee653e,

	0x3f04b84d, 0x945d0c9c, 0x7b0be704, 0xd05253d5, 0x2db88ea6, 0x86e13a77,

	0x7d348091, 0xd66d3440, 0x2b87e933, 0x80de5de2, 0x7775282e, 0xdc2c9cff,

	0x21c6418c, 0x8a9ff55d, 0x714a4fbb, 0xda13fb6a, 0x27f92619, 0x8ca092c8,

	0x520d45f8, 0xf954f129, 0x04be2c5a, 0xafe7988b, 0x5432226d, 0xff6b96bc,

	0x02814bcf, 0xa9d8ff1e, 0x5e738ad2, 0xf52a3e03, 0x08c0e370, 0xa39957a1,

	0x584ced47, 0xf3155996, 0x0eff84e5, 0xa5a63034, 0x4af0dbac, 0xe1a96f7d,

	0x1c43b20e, 0xb71a06df, 0x4ccfbc39, 0xe79608e8, 0x1a7cd59b, 0xb125614a,

	0x468e1486, 0xedd7a057, 0x103d7d24, 0xbb64c9f5, 0x40b17313, 0xebe8c7c2,

	0x16021ab1, 0xbd5bae60, 0x6cb54671, 0xc7ecf2a0, 0x3a062fd3, 0x915f9b02,

	0x6a8a21e4, 0xc1d39535, 0x3c394846, 0x9760fc97, 0x60cb895b, 0xcb923d8a,

	0x3678e0f9, 0x9d215428, 0x66f4eece, 0xcdad5a1f, 0x3047876c, 0x9b1e33bd,

	0x7448d825, 0xdf116cf4, 0x22fbb187, 0x89a20556, 0x7277bfb0, 0xd92e0b61,

	0x24c4d612, 0x8f9d62c3, 0x7836170f, 0xd36fa3de, 0x2e857ead, 0x85dcca7c,

	0x7e09709a, 0xd550c44b, 0x28ba1938, 0x83e3ade9, 0x5d4e7ad9, 0xf617ce08,

	0x0bfd137b, 0xa0a4a7aa, 0x5b711d4c, 0xf028a99d, 0x0dc274ee, 0xa69bc03f,

	0x5130b5f3, 0xfa690122, 0x0783dc51, 0xacda6880, 0x570fd266, 0xfc5666b7,

	0x01bcbbc4, 0xaae50f15, 0x45b3e48d, 0xeeea505c, 0x13008d2f, 0xb85939fe,

	0x438c8318, 0xe8d537c9, 0x153feaba, 0xbe665e6b, 0x49cd2ba7, 0xe2949f76,

	0x1f7e4205, 0xb427f6d4, 0x4ff24c32, 0xe4abf8e3, 0x19412590, 0xb2189141,

	0x0f433f21, 0xa41a8bf0, 0x59f05683, 0xf2a9e252, 0x097c58b4, 0xa225ec65,

	0x5fcf3116, 0xf49685c7, 0x033df00b, 0xa86444da, 0x558e99a9, 0xfed72d78,

	0x0502979e, 0xae5b234f, 0x53b1fe3c, 0xf8e84aed, 0x17bea175, 0xbce715a4,

	0x410dc8d7, 0xea547c06, 0x1181c6e0, 0xbad87231, 0x4732af42, 0xec6b1b93,

	0x1bc06e5f, 0xb099da8e, 0x4d7307fd, 0xe62ab32c, 0x1dff09ca, 0xb6a6bd1b,

	0x4b4c6068, 0xe015d4b9, 0x3eb80389, 0x95e1b758, 0x680b6a2b, 0xc352defa,

	0x3887641c, 0x93ded0cd, 0x6e340dbe, 0xc56db96f, 0x32c6cca3, 0x999f7872,

	0x6475a501, 0xcf2c11d0, 0x34f9ab36, 0x9fa01fe7, 0x624ac294, 0xc9137645,

	0x26459ddd, 0x8d1c290c, 0x70f6f47f, 0xdbaf40ae, 0x207afa48, 0x8b234e99,

	0x76c993ea, 0xdd90273b, 0x2a3b52f7, 0x8162e626, 0x7c883b55, 0xd7d18f84,

	0x2c043562, 0x875d81b3, 0x7ab75cc0, 0xd1eee811

};

static const unsigned int U[256] = {

	0x00000000, 0x7eb5200d, 0x5633f4cb, 0x2886d4c6, 0x073e5d47, 0x798b7d4a,

	0x510da98c, 0x2fb88981, 0x0e7cba8e, 0x70c99a83, 0x584f4e45, 0x26fa6e48,

	0x0942e7c9, 0x77f7c7c4, 0x5f711302, 0x21c4330f, 0x1cf9751c, 0x624c5511,

	0x4aca81d7, 0x347fa1da, 0x1bc7285b, 0x65720856, 0x4df4dc90, 0x3341fc9d,

	0x1285cf92, 0x6c30ef9f, 0x44b63b59, 0x3a031b54, 0x15bb92d5, 0x6b0eb2d8,

	0x4388661e, 0x3d3d4613, 0x39f2ea38, 0x4747ca35, 0x6fc11ef3, 0x11743efe,

	0x3eccb77f, 0x40799772, 0x68ff43b4, 0x164a63b9, 0x378e50b6, 0x493b70bb,

	0x61bda47d, 0x1f088470, 0x30b00df1, 0x4e052dfc, 0x6683f93a, 0x1836d937,

	0x250b9f24, 0x5bbebf29, 0x73386bef, 0x0d8d4be2, 0x2235c263, 0x5c80e26e,

	0x740636a8, 0x0ab316a5, 0x2b7725aa, 0x55c205a7, 0x7d44d161, 0x03f1f16c,

	0x2c4978ed, 0x52fc58e0, 0x7a7a8c26, 0x04cfac2b, 0x73e5d470, 0x0d50f47d,

	0x25d620bb, 0x5b6300b6, 0x74db8937, 0x0a6ea93a, 0x22e87dfc, 0x5c5d5df1,

	0x7d996efe, 0x032c4ef3, 0x2baa9a35, 0x551fba38, 0x7aa733b9, 0x041213b4,

	0x2c94c772, 0x5221e77f, 0x6f1ca16c, 0x11a98161, 0x392f55a7, 0x479a75aa,

	0x6822fc2b, 0x1697dc26, 0x3e1108e0, 0x40a428ed, 0x61601be2, 0x1fd53bef,

	0x3753ef29, 0x49e6cf24, 0x665e46a5, 0x18eb66a8, 0x306db26e, 0x4ed89263,

	0x4a173e48, 0x34a21e45, 0x1c24ca83, 0x6291ea8e, 0x4d29630f, 0x339c4302,

	0x1b1a97c4, 0x65afb7c9, 0x446b84c6, 0x3adea4cb, 0x1258700d, 0x6ced5000,

	0x4355d981, 0x3de0f98c, 0x15662d4a, 0x6bd30d47, 0x56ee4b54, 0x285b6b59,

	0x00ddbf9f, 0x7e689f92, 0x51d01613, 0x2f65361e, 0x07e3e2d8, 0x7956c2d5,

	0x5892f1da, 0x2627d1d7, 0x0ea10511, 0x7014251c, 0x5facac9d, 0x21198c90,

	0x099f5856, 0x772a785b, 0x4c921c31, 0x32273c3c, 0x1aa1e8fa, 0x6414c8f7,

	0x4bac4176, 0x3519617b, 0x1d9fb5bd, 0x632a95b0, 0x42eea6bf, 0x3c5b86b2,

	0x14dd5274, 0x6a687279, 0x45d0fbf8, 0x3b65dbf5, 0x13e30f33, 0x6d562f3e,

	0x506b692d, 0x2ede4920, 0x06589de6, 0x78edbdeb, 0x5755346a, 0x29e01467,

	0x0166c0a1, 0x7fd3e0ac, 0x5e17d3a3, 0x20a2f3ae, 0x08242768, 0x76910765,

	0x59298ee4, 0x279caee9, 0x0f1a7a2f, 0x71af5a22, 0x7560f609, 0x0bd5d604,

	0x235302c2, 0x5de622cf, 0x725eab4e, 0x0ceb8b43, 0x246d5f85, 0x5ad87f88,

	0x7b1c4c87, 0x05a96c8a, 0x2d2fb84c, 0x539a9841, 0x7c2211c0, 0x029731cd,

	0x2a11e50b, 0x54a4c506, 0x69998315, 0x172ca318, 0x3faa77de, 0x411f57d3,

	0x6ea7de52, 0x1012fe5f, 0x38942a99, 0x46210a94, 0x67e5399b, 0x19501996,

	0x31d6cd50, 0x4f63ed5d, 0x60db64dc, 0x1e6e44d1, 0x36e89017, 0x485db01a,

	0x3f77c841, 0x41c2e84c, 0x69443c8a, 0x17f11c87, 0x38499506, 0x46fcb50b,

	0x6e7a61cd, 0x10cf41c0, 0x310b72cf, 0x4fbe52c2, 0x67388604, 0x198da609,

	0x36352f88, 0x48800f85, 0x6006db43, 0x1eb3fb4e, 0x238ebd5d, 0x5d3b9d50,

	0x75bd4996, 0x0b08699b, 0x24b0e01a, 0x5a05c017, 0x728314d1, 0x0c3634dc,

	0x2df207d3, 0x534727de, 0x7bc1f318, 0x0574d315, 0x2acc5a94, 0x54797a99,

	0x7cffae5f, 0x024a8e52, 0x06852279, 0x78300274, 0x50b6d6b2, 0x2e03f6bf,

	0x01bb7f3e, 0x7f0e5f33, 0x57888bf5, 0x293dabf8, 0x08f998f7, 0x764cb8fa,

	0x5eca6c3c, 0x207f4c31, 0x0fc7c5b0, 0x7172e5bd, 0x59f4317b, 0x27411176,

	0x1a7c5765, 0x64c97768, 0x4c4fa3ae, 0x32fa83a3, 0x1d420a22, 0x63f72a2f,

	0x4b71fee9, 0x35c4dee4, 0x1400edeb, 0x6ab5cde6, 0x42331920, 0x3c86392d,

	0x133eb0ac, 0x6d8b90a1, 0x450d4467, 0x3bb8646a

};

struct index_entry {

	const unsigned char *ptr;

	const struct source_info *src;

	unsigned int val;

};

struct unpacked_index_entry {

	struct index_entry entry;

	struct unpacked_index_entry *next;

};

struct delta_index {

	unsigned long memsize; /* Total bytes pointed to by this index */

	const struct source_info *last_src; /* Information about the referenced source */

	unsigned int hash_mask; /* val & hash_mask gives the hash index for a given

							   entry */

	unsigned int num_entries; /* The total number of entries in this index */

	struct index_entry *last_entry; /* Pointer to the last valid entry */

	struct index_entry *hash[];

};

static unsigned int

limit_hash_buckets(struct unpacked_index_entry **hash,

				   unsigned int *hash_count, unsigned int hsize,

				   unsigned int entries)

{

	struct unpacked_index_entry *entry;

	unsigned int i;

	/*

	 * Determine a limit on the number of entries in the same hash

	 * bucket.	This guards us against pathological data sets causing

	 * really bad hash distribution with most entries in the same hash

	 * bucket that would bring us to O(m*n) computing costs (m and n

	 * corresponding to reference and target buffer sizes).

	 *

	 * Make sure none of the hash buckets has more entries than

	 * we're willing to test.  Otherwise we cull the entry list

	 * uniformly to still preserve a good repartition across

	 * the reference buffer.

	 */

	for (i = 0; i < hsize; i++) {

		int acc;

		if (hash_count[i] <= HASH_LIMIT)

			continue;

		/* We leave exactly HASH_LIMIT entries in the bucket */

		entries -= hash_count[i] - HASH_LIMIT;

		entry = hash[i];

		acc = 0;

		/*

		 * Assume that this loop is gone through exactly

		 * HASH_LIMIT times and is entered and left with

		 * acc==0.	So the first statement in the loop

		 * contributes (hash_count[i]-HASH_LIMIT)*HASH_LIMIT

		 * to the accumulator, and the inner loop consequently

		 * is run (hash_count[i]-HASH_LIMIT) times, removing

		 * one element from the list each time.  Since acc

		 * balances out to 0 at the final run, the inner loop

		 * body can't be left with entry==NULL.  So we indeed

		 * encounter entry==NULL in the outer loop only.

		 */

		do {

			acc += hash_count[i] - HASH_LIMIT;

			if (acc > 0) {

				struct unpacked_index_entry *keep = entry;

				do {

					entry = entry->next;

					acc -= HASH_LIMIT;

				} while (acc > 0);

				keep->next = entry->next;

			}

			entry = entry->next;

		} while (entry);

	}

	return entries;

}

static struct delta_index *

pack_delta_index(struct unpacked_index_entry **hash, unsigned int hsize,

				 unsigned int num_entries)

{

	unsigned int i, memsize;

	struct unpacked_index_entry *entry;

	struct delta_index *index;

	struct index_entry *packed_entry, **packed_hash;

	void *mem;

	/*

	 * Now create the packed index in array form

	 * rather than linked lists.

	 */

	memsize = sizeof(*index)

		+ sizeof(*packed_hash) * (hsize+1)

		+ sizeof(*packed_entry) * num_entries;

	mem = malloc(memsize);

	if (!mem) {

		return NULL;

	}

	index = mem;

	index->memsize = memsize;

	index->hash_mask = hsize - 1;

	index->num_entries = num_entries;

	mem = index->hash;

	packed_hash = mem;

	mem = packed_hash + (hsize+1);

	packed_entry = mem;

	for (i = 0; i < hsize; i++) {

		/*

		 * Coalesce all entries belonging to one linked list

		 * into consecutive array entries.

		 */

		packed_hash[i] = packed_entry;

		for (entry = hash[i]; entry; entry = entry->next)

			*packed_entry++ = entry->entry;

	}

	/* Sentinel value to indicate the length of the last hash bucket */

	packed_hash[hsize] = packed_entry;

	assert(packed_entry - (struct index_entry *)mem == num_entries);

	index->last_entry = (packed_entry - 1);

	return index;

}

void include_entries_from_index(struct unpacked_index_entry **hash,

								unsigned int *hash_count,

								unsigned int hsize,

								struct unpacked_index_entry *entry,

								const struct delta_index *old)

{

	unsigned int i, hmask, masked_val;

	struct index_entry *old_entry;

	hmask = hsize - 1;

	/* Iterate backwards through the existing entries

	 * This is so that matches early in the file end up being the first pointer

	 * in the linked list.

	 * TODO: We know that all old entries are going to occur before the new

	 *		 entries, and that we are going to follow this with a limit and

	 *		 then pack step. There is probably a way we could optimize this

	 *		 step, so that we wouldn't have to copy everything into a new

	 *		 buffer, and then copy everything again into yet another buffer.

	 */

	for (old_entry = old->last_entry, i = 0; i < old->num_entries;

		 i++, old_entry--) {

		masked_val = old_entry->val & hmask;

		entry->entry = *old_entry;

		entry->next = hash[masked_val];

		hash[masked_val] = entry++;

		hash_count[masked_val]++;

	}

}

struct delta_index *

create_index_from_old_and_hash(const struct delta_index *old,

							   struct unpacked_index_entry **hash,

							   unsigned int hsize,

							   unsigned int num_entries)

{

	unsigned int i, memsize, total_num_entries;

	struct unpacked_index_entry *entry;

	struct delta_index *index;

	struct index_entry *packed_entry, **packed_hash;

	struct index_entry *copy_from_start, *copy_to_start;

	size_t total_copy, to_copy;

	unsigned int num_ops;

	unsigned int bytes_copied;

	void *mem;

	/*

	 * Now create the packed index in array form

	 * rather than linked lists.

	 */

	total_num_entries = num_entries + old->num_entries;

	memsize = sizeof(*index)

		+ sizeof(*packed_hash) * (hsize+1)

		+ sizeof(*packed_entry) * total_num_entries;

	mem = malloc(memsize);

	if (!mem) {

		return NULL;

	}

	index = mem;

	index->memsize = memsize;

	index->hash_mask = hsize - 1;

	index->num_entries = total_num_entries;

	mem = index->hash;

	packed_hash = mem;

	mem = packed_hash + (hsize+1);

	packed_entry = mem;

	total_copy = 0;

	bytes_copied = 0;

	num_ops = 0;

	copy_from_start = copy_to_start = NULL;

	for (i = 0; i < hsize; i++) {

		/*

		 * Coalesce all entries belonging to one linked list

		 * into consecutive array entries.

		 * The entries in old all come before the entries in hash.

		 */

		packed_hash[i] = packed_entry;

		to_copy = (old->hash[i+1] - old->hash[i]);

		if (to_copy > 0) {

			/* This next range can be copied wholesale. However, we will wait

			 * until we have to insert something from the new data before we

			 * copy everything.

			 * So for now, just reserve space for the copy.

			 */

			if (total_copy == 0) {

				copy_from_start = old->hash[i];

				copy_to_start = packed_entry;

			}

			packed_entry += to_copy;

			total_copy += to_copy;

			assert((packed_entry - copy_to_start) == total_copy);

			assert((old->hash[i+1] - copy_from_start) == total_copy);

		}

		for (entry = hash[i]; entry; entry = entry->next) {

			/* We have an entry to insert, so flush the copy buffer */

			if (total_copy > 0) {

				assert(copy_to_start != NULL);

				assert(copy_from_start != NULL);

				memcpy(copy_to_start, copy_from_start,

					   total_copy * sizeof(struct index_entry));

				bytes_copied += (total_copy * sizeof(struct index_entry));

				total_copy = 0;

				copy_from_start = copy_to_start = NULL;

				num_ops += 1;

			}

			*packed_entry++ = entry->entry;

		}

	}

	if (total_copy > 0) {

		assert(copy_to_start != NULL);

		assert(copy_from_start != NULL);

		memcpy(copy_to_start, copy_from_start,

			   total_copy * sizeof(struct index_entry));

		bytes_copied += (total_copy * sizeof(struct index_entry));

		num_ops += 1;

	}

	/* Sentinel value to indicate the length of the last hash bucket */

	packed_hash[hsize] = packed_entry;

	assert(packed_entry - (struct index_entry *)mem == total_num_entries);

	index->last_entry = (packed_entry - 1);

	return index;

}

struct delta_index * create_delta_index(const struct source_info *src,

										const struct delta_index *old)

{

	unsigned int i, hsize, hmask, num_entries, prev_val, *hash_count;

	unsigned int total_num_entries;

	const unsigned char *data, *buffer;

	struct delta_index *index;

	struct unpacked_index_entry *entry, **hash;

	void *mem;

	unsigned long memsize;

	if (!src->buf || !src->size)

		return NULL;

	buffer = src->buf;

	/* Determine index hash size.  Note that indexing skips the

	   first byte to allow for optimizing the Rabin's polynomial

	   initialization in create_delta(). */

	num_entries = (src->size - 1)  / RABIN_WINDOW;

	if (old != NULL)

		total_num_entries = num_entries + old->num_entries;

	else

		total_num_entries = num_entries;

	hsize = total_num_entries / 4;

	for (i = 4; (1u << i) < hsize && i < 31; i++);

	hsize = 1 << i;

	hmask = hsize - 1;

	/* allocate lookup index */

	memsize = sizeof(*hash) * hsize +

		  sizeof(*entry) * total_num_entries;

	mem = malloc(memsize);

	if (!mem)

		return NULL;

	hash = mem;

	mem = hash + hsize;

	entry = mem;

	memset(hash, 0, hsize * sizeof(*hash));

	/* allocate an array to count hash num_entries */

	hash_count = calloc(hsize, sizeof(*hash_count));

	if (!hash_count) {

		free(hash);

		return NULL;

	}

	/* then populate the index for the new data */

	prev_val = ~0;

	for (data = buffer + num_entries * RABIN_WINDOW - RABIN_WINDOW;

		 data >= buffer;

		 data -= RABIN_WINDOW) {

		unsigned int val = 0;

		for (i = 1; i <= RABIN_WINDOW; i++)

			val = ((val << 8) | data[i]) ^ T[val >> RABIN_SHIFT];

		if (val == prev_val) {

			/* keep the lowest of consecutive identical blocks */

			entry[-1].entry.ptr = data + RABIN_WINDOW;

			--num_entries;

			--total_num_entries;

		} else {

			prev_val = val;

			i = val & hmask;

			entry->entry.ptr = data + RABIN_WINDOW;

			entry->entry.val = val;

			entry->entry.src = src;

			entry->next = hash[i];

			hash[i] = entry++;

			hash_count[i]++;

		}

	}

	/* If we have an existing delta_index, we want to bring its info into the

	 * new structure. We assume that the existing structure's objects all occur

	 * before the new source, so they get first precedence in the index.

	 */

	if (old != NULL)

		include_entries_from_index(hash, hash_count, hsize, entry, old);

	total_num_entries = limit_hash_buckets(hash, hash_count, hsize,

										   total_num_entries);

	free(hash_count);

	index = pack_delta_index(hash, hsize, total_num_entries);

	index->last_src = src;

	free(hash);

	if (!index) {

		return NULL;

	}

	return index;

}

struct delta_index * create_delta_index_from_delta(

										const struct source_info *src,

										const struct delta_index *old)

{

	unsigned int i, hsize, hmask, num_entries, prev_val, *hash_count;

	unsigned int total_num_entries;

	const unsigned char *data, *buffer, *top;

	unsigned char cmd;

	struct delta_index *index;

	struct unpacked_index_entry *entry, **hash;

	void *mem;

	unsigned long memsize;

	if (!src->buf || !src->size)

		return NULL;

	buffer = src->buf;

	top = buffer + src->size;

	/* Determine index hash size.  Note that indexing skips the

	   first byte to allow for optimizing the Rabin's polynomial

	   initialization in create_delta().

	   This computes the maximum number of entries that could be held. The

	   actual number will be recomputed during processing.

	   */

	num_entries = (src->size - 1)  / RABIN_WINDOW;

	if (old != NULL)

		total_num_entries = num_entries + old->num_entries;

	else

		total_num_entries = num_entries;

	hsize = total_num_entries / 4;

	for (i = 4; (1u << i) < hsize && i < 31; i++);

	hsize = 1 << i;

	hmask = hsize - 1;

	/* allocate lookup index */

	memsize = sizeof(*hash) * hsize +

		  sizeof(*entry) * total_num_entries;

	mem = malloc(memsize);

	if (!mem)

		return NULL;

	hash = mem;

	mem = hash + hsize;

	entry = mem;

	memset(hash, 0, hsize * sizeof(*hash));

	/* allocate an array to count hash num_entries */

	hash_count = calloc(hsize, sizeof(*hash_count));

	if (!hash_count) {

		free(hash);

		return NULL;

	}

	/* then populate the index for the new data */

	/* The create_delta_index code starts at the end and works backward,

	 * because it is easier to update the entry pointers (you always update the

	 * head, rather than updating the tail).

	 * However, we can't walk the delta structure that way.

	 */

	prev_val = ~0;

	data = buffer;