thodg/libgit2

diff --git a/src/delta.c b/src/delta.c
new file mode 100644
index 0000000..49f7df0
--- /dev/null
+++ b/src/delta.c
@@ -0,0 +1,491 @@
+/*
+ * 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@fluxnic.net>, (C) 2005-2007
+ *
+ * Modified for libgit2 by Michael Schubert <schu@schu.io>, (C) 2012
+ *
+ * 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"
+
+/* 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;
+	unsigned int val;
+};
+
+struct unpacked_index_entry {
+	struct index_entry entry;
+	struct unpacked_index_entry *next;
+};
+
+struct git_delta_index {
+	unsigned long memsize;
+	const void *src_buf;
+	unsigned long src_size;
+	unsigned int hash_mask;
+	struct index_entry *hash[GIT_FLEX_ARRAY];
+};
+
+struct git_delta_index *
+git_delta_create_index(const void *buf, unsigned long bufsize)
+{
+	unsigned int i, hsize, hmask, entries, prev_val, *hash_count;
+	const unsigned char *data, *buffer = buf;
+	struct git_delta_index *index;
+	struct unpacked_index_entry *entry, **hash;
+	struct index_entry *packed_entry, **packed_hash;
+	void *mem;
+	unsigned long memsize;
+
+	if (!buf || !bufsize)
+		return NULL;
+
+	/* Determine index hash size.  Note that indexing skips the
+	   first byte to allow for optimizing the Rabin's polynomial
+	   initialization in create_delta(). */
+	entries = (bufsize - 1) / RABIN_WINDOW;
+	if (bufsize >= 0xffffffffUL) {
+		/*
+		 * Current delta format can't encode offsets into
+		 * reference buffer with more than 32 bits.
+		 */
+		entries = 0xfffffffeU / RABIN_WINDOW;
+	}
+	hsize = 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) * entries;
+	mem = git__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 entries */
+	hash_count = calloc(hsize, sizeof(*hash_count));
+	if (!hash_count) {
+		git__free(hash);
+		return NULL;
+	}
+
+	/* then populate the index */
+	prev_val = ~0;
+	for (data = buffer + 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;
+			--entries;
+		} else {
+			prev_val = val;
+			i = val & hmask;
+			entry->entry.ptr = data + RABIN_WINDOW;
+			entry->entry.val = val;
+			entry->next = hash[i];
+			hash[i] = entry++;
+			hash_count[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);
+	}
+	git__free(hash_count);
+
+	/*
+	 * Now create the packed index in array form
+	 * rather than linked lists.
+	 */
+	memsize = sizeof(*index)
+		+ sizeof(*packed_hash) * (hsize+1)
+		+ sizeof(*packed_entry) * entries;
+	mem = git__malloc(memsize);
+	if (!mem) {
+		git__free(hash);
+		return NULL;
+	}
+
+	index = mem;
+	index->memsize = memsize;
+	index->src_buf = buf;
+	index->src_size = bufsize;
+	index->hash_mask = hmask;
+
+	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 == entries);
+	git__free(hash);
+
+	return index;
+}
+
+void git_delta_free_index(struct git_delta_index *index)
+{
+	git__free(index);
+}
+
+unsigned long git_delta_sizeof_index(struct git_delta_index *index)
+{
+	if (index)
+		return index->memsize;
+	else
+		return 0;
+}
+
+/*
+ * The maximum size for any opcode sequence, including the initial header
+ * plus Rabin window plus biggest copy.
+ */
+#define MAX_OP_SIZE	(5 + 5 + 1 + RABIN_WINDOW + 7)
+
+void *
+git_delta_create(const struct git_delta_index *index,
+		 const void *trg_buf, unsigned long trg_size,
+		 unsigned long *delta_size, unsigned long max_size)
+{
+	unsigned int i, outpos, outsize, moff, msize, val;
+	int inscnt;
+	const unsigned char *ref_data, *ref_top, *data, *top;
+	unsigned char *out;
+
+	if (!trg_buf || !trg_size)
+		return NULL;
+
+	outpos = 0;
+	outsize = 8192;
+	if (max_size && outsize >= max_size)
+		outsize = max_size + MAX_OP_SIZE + 1;
+	out = git__malloc(outsize);
+	if (!out)
+		return NULL;
+
+	/* store reference buffer size */
+	i = index->src_size;
+	while (i >= 0x80) {
+		out[outpos++] = i | 0x80;
+		i >>= 7;
+	}
+	out[outpos++] = i;
+
+	/* store target buffer size */
+	i = trg_size;
+	while (i >= 0x80) {
+		out[outpos++] = i | 0x80;
+		i >>= 7;
+	}
+	out[outpos++] = i;
+
+	ref_data = index->src_buf;
+	ref_top = ref_data + index->src_size;
+	data = trg_buf;
+	top = (const unsigned char *) trg_buf + trg_size;
+
+	outpos++;
+	val = 0;
+	for (i = 0; i < RABIN_WINDOW && data < top; i++, data++) {
+		out[outpos++] = *data;
+		val = ((val << 8) | *data) ^ T[val >> RABIN_SHIFT];
+	}
+	inscnt = i;
+
+	moff = 0;
+	msize = 0;
+	while (data < top) {
+		if (msize < 4096) {
+			struct index_entry *entry;
+			val ^= U[data[-RABIN_WINDOW]];
+			val = ((val << 8) | *data) ^ T[val >> RABIN_SHIFT];
+			i = val & index->hash_mask;
+			for (entry = index->hash[i]; entry < index->hash[i+1]; entry++) {
+				const unsigned char *ref = entry->ptr;
+				const unsigned char *src = data;
+				unsigned int ref_size = ref_top - ref;
+				if (entry->val != val)
+					continue;
+				if (ref_size > (unsigned int)(top - src))
+					ref_size = top - src;
+				if (ref_size <= msize)
+					break;
+				while (ref_size-- && *src++ == *ref)
+					ref++;
+				if (msize < (unsigned int)(ref - entry->ptr)) {
+					/* this is our best match so far */
+					msize = ref - entry->ptr;
+					moff = entry->ptr - ref_data;
+					if (msize >= 4096) /* good enough */
+						break;
+				}
+			}
+		}
+
+		if (msize < 4) {
+			if (!inscnt)
+				outpos++;
+			out[outpos++] = *data++;
+			inscnt++;
+			if (inscnt == 0x7f) {
+				out[outpos - inscnt - 1] = inscnt;
+				inscnt = 0;
+			}
+			msize = 0;
+		} else {
+			unsigned int left;
+			unsigned char *op;
+
+			if (inscnt) {
+				while (moff && ref_data[moff-1] == data[-1]) {
+					/* we can match one byte back */
+					msize++;
+					moff--;
+					data--;
+					outpos--;
+					if (--inscnt)
+						continue;
+					outpos--;  /* remove count slot */
+					inscnt--;  /* make it -1 */
+					break;
+				}
+				out[outpos - inscnt - 1] = inscnt;
+				inscnt = 0;
+			}
+
+			/* A copy op is currently limited to 64KB (pack v2) */
+			left = (msize < 0x10000) ? 0 : (msize - 0x10000);
+			msize -= left;
+
+			op = out + outpos++;
+			i = 0x80;
+
+			if (moff & 0x000000ff)
+				out[outpos++] = moff >> 0,  i |= 0x01;
+			if (moff & 0x0000ff00)
+				out[outpos++] = moff >> 8,  i |= 0x02;
+			if (moff & 0x00ff0000)
+				out[outpos++] = moff >> 16, i |= 0x04;
+			if (moff & 0xff000000)
+				out[outpos++] = moff >> 24, i |= 0x08;
+
+			if (msize & 0x00ff)
+				out[outpos++] = msize >> 0, i |= 0x10;
+			if (msize & 0xff00)
+				out[outpos++] = msize >> 8, i |= 0x20;
+
+			*op = i;
+
+			data += msize;
+			moff += msize;
+			msize = left;
+
+			if (msize < 4096) {
+				int j;
+				val = 0;
+				for (j = -RABIN_WINDOW; j < 0; j++)
+					val = ((val << 8) | data[j])
+					      ^ T[val >> RABIN_SHIFT];
+			}
+		}
+
+		if (outpos >= outsize - MAX_OP_SIZE) {
+			void *tmp = out;
+			outsize = outsize * 3 / 2;
+			if (max_size && outsize >= max_size)
+				outsize = max_size + MAX_OP_SIZE + 1;
+			if (max_size && outpos > max_size)
+				break;
+			out = git__realloc(out, outsize);
+			if (!out) {
+				git__free(tmp);
+				return NULL;
+			}
+		}
+	}
+
+	if (inscnt)
+		out[outpos - inscnt - 1] = inscnt;
+
+	if (max_size && outpos > max_size) {
+		git__free(out);
+		return NULL;
+	}
+
+	*delta_size = outpos;
+	return out;
+}
diff --git a/src/delta.h b/src/delta.h
new file mode 100644
index 0000000..b0b8e41
--- /dev/null
+++ b/src/delta.h
@@ -0,0 +1,112 @@
+/*
+ * diff-delta code taken from git.git. See diff-delta.c for details.
+ *
+ */
+#ifndef INCLUDE_git_delta_h__
+#define INCLUDE_git_delta_h__
+
+#include "common.h"
+
+/* opaque object for delta index */
+struct git_delta_index;
+
+/*
+ * create_delta_index: compute index data from given buffer
+ *
+ * This returns a pointer to a struct delta_index that should be passed to
+ * subsequent create_delta() calls, or to free_delta_index().  A NULL pointer
+ * is returned on failure.  The given buffer must not be freed nor altered
+ * before free_delta_index() is called.  The returned pointer must be freed
+ * using free_delta_index().
+ */
+extern struct git_delta_index *
+git_delta_create_index(const void *buf, unsigned long bufsize);
+
+/*
+ * free_delta_index: free the index created by create_delta_index()
+ *
+ * Given pointer must be what create_delta_index() returned, or NULL.
+ */
+extern void git_delta_free_index(struct git_delta_index *index);
+
+/*
+ * sizeof_delta_index: returns memory usage of delta index
+ *
+ * Given pointer must be what create_delta_index() returned, or NULL.
+ */
+extern unsigned long git_delta_sizeof_index(struct git_delta_index *index);
+
+/*
+ * create_delta: create a delta from given index for the given buffer
+ *
+ * This function may be called multiple times with different buffers using
+ * the same delta_index pointer.  If max_delta_size is non-zero and the
+ * resulting delta is to be larger than max_delta_size then NULL is returned.
+ * On success, a non-NULL pointer to the buffer with the delta data is
+ * returned and *delta_size is updated with its size.  The returned buffer
+ * must be freed by the caller.
+ */
+extern void *
+git_delta_create(const struct git_delta_index *index,
+		 const void *buf, unsigned long bufsize,
+		 unsigned long *delta_size,
+		 unsigned long max_delta_size);
+
+/*
+ * diff_delta: create a delta from source buffer to target buffer
+ *
+ * If max_delta_size is non-zero and the resulting delta is to be larger
+ * than max_delta_size then NULL is returned.  On success, a non-NULL
+ * pointer to the buffer with the delta data is returned and *delta_size is
+ * updated with its size.  The returned buffer must be freed by the caller.
+ */
+GIT_INLINE(void *)
+git_delta(const void *src_buf, unsigned long src_bufsize,
+	  const void *trg_buf, unsigned long trg_bufsize,
+	  unsigned long *delta_size, unsigned long max_delta_size)
+{
+	struct git_delta_index *index = git_delta_create_index(src_buf, src_bufsize);
+	if (index) {
+		void *delta = git_delta_create(index, trg_buf, trg_bufsize,
+					       delta_size, max_delta_size);
+		git_delta_free_index(index);
+		return delta;
+	}
+	return NULL;
+}
+
+/*
+ * patch_delta: recreate target buffer given source buffer and delta data
+ *
+ * On success, a non-NULL pointer to the target buffer is returned and
+ * *trg_bufsize is updated with its size.  On failure a NULL pointer is
+ * returned.  The returned buffer must be freed by the caller.
+ */
+extern void *git_delta_patch(const void *src_buf, unsigned long src_size,
+			     const void *delta_buf, unsigned long delta_size,
+			     unsigned long *dst_size);
+
+/* the smallest possible delta size is 4 bytes */
+#define GIT_DELTA_SIZE_MIN	4
+
+/*
+ * This must be called twice on the delta data buffer, first to get the
+ * expected source buffer size, and again to get the target buffer size.
+ */
+GIT_INLINE(unsigned long)
+git_delta_get_hdr_size(const unsigned char **datap,
+		       const unsigned char *top)
+{
+	const unsigned char *data = *datap;
+	unsigned long cmd, size = 0;
+	int i = 0;
+	do {
+		cmd = *data++;
+		size |= (cmd & 0x7f) << i;
+		i += 7;
+	} while (cmd & 0x80 && data < top);
+	*datap = data;
+	return size;
+}
+
+#endif