Merge branch 'np/pack'
[gitweb.git] / diff-delta.c
index aaee7be4d20dade99d351f6bdd70632cf249230e..25a798d050c6319f3d524c9c605ab70ea35ae7a1 100644 (file)
 
 #include <stdlib.h>
 #include <string.h>
-#include <zlib.h>
 #include "delta.h"
 
 
-/* block size: min = 16, max = 64k, power of 2 */
-#define BLK_SIZE 16
-
-#define MIN(a, b) ((a) < (b) ? (a) : (b))
+/* 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
+};
 
-#define GR_PRIME 0x9e370001
-#define HASH(v, shift) (((unsigned int)(v) * GR_PRIME) >> (shift))
+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 {
+struct index_entry {
        const unsigned char *ptr;
        unsigned int val;
-       struct index *next;
+       struct index_entry *next;
+};
+
+struct delta_index {
+       const void *src_buf;
+       unsigned long src_size;
+       unsigned int hash_mask;
+       struct index_entry *hash[0];
 };
 
-static struct index ** delta_index(const unsigned char *buf,
-                                  unsigned long bufsize,
-                                  unsigned long trg_bufsize,
-                                  unsigned int *hash_shift)
+struct delta_index * create_delta_index(const void *buf, unsigned long bufsize)
 {
-       unsigned int i, hsize, hshift, hlimit, entries, *hash_count;
-       const unsigned char *data;
-       struct index *entry, **hash;
+       unsigned int i, hsize, hmask, entries, prev_val, *hash_count;
+       const unsigned char *data, *buffer = buf;
+       struct delta_index *index;
+       struct index_entry *entry, **hash;
        void *mem;
+       unsigned long memsize;
 
-       /* determine index hash size */
-       entries = bufsize  / BLK_SIZE;
+       if (!buf || !bufsize)
+               return NULL;
+
+       /* Determine index hash size.  Note that indexing skips the
+          first byte to allow for optimizing the rabin polynomial
+          initialization in create_delta(). */
+       entries = (bufsize - 1)  / RABIN_WINDOW;
        hsize = entries / 4;
        for (i = 4; (1 << i) < hsize && i < 31; i++);
        hsize = 1 << i;
-       hshift = 32 - i;
-       *hash_shift = hshift;
+       hmask = hsize - 1;
 
        /* allocate lookup index */
-       mem = malloc(hsize * sizeof(*hash) + entries * sizeof(*entry));
+       memsize = sizeof(*index) +
+                 sizeof(*hash) * hsize +
+                 sizeof(*entry) * entries;
+       mem = malloc(memsize);
        if (!mem)
                return NULL;
+       index = mem;
+       mem = index + 1;
        hash = mem;
-       entry = mem + hsize * sizeof(*hash);
+       mem = hash + hsize;
+       entry = mem;
+
+       index->src_buf = buf;
+       index->src_size = bufsize;
+       index->hash_mask = hmask;
        memset(hash, 0, hsize * sizeof(*hash));
 
        /* allocate an array to count hash entries */
        hash_count = calloc(hsize, sizeof(*hash_count));
        if (!hash_count) {
-               free(hash);
+               free(index);
                return NULL;
        }
 
        /* then populate the index */
-       data = buf + entries * BLK_SIZE - BLK_SIZE;
-       while (data >= buf) {
-               unsigned int val = adler32(0, data, BLK_SIZE);
-               i = HASH(val, hshift);
-               entry->ptr = data;
-               entry->val = val;
-               entry->next = hash[i];
-               hash[i] = entry++;
-               hash_count[i]++;
-               data -= BLK_SIZE;
-       }
+       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].ptr = data + RABIN_WINDOW;
+               } else {
+                       prev_val = val;
+                       i = val & hmask;
+                       entry->ptr = data + RABIN_WINDOW;
+                       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
@@ -91,27 +209,18 @@ static struct index ** delta_index(const unsigned char *buf,
         * bucket that would bring us to O(m*n) computing costs (m and n
         * corresponding to reference and target buffer sizes).
         *
-        * The more the target buffer is large, the more it is important to
-        * have small entry lists for each hash buckets.  With such a limit
-        * the cost is bounded to something more like O(m+n).
-        */
-       hlimit = (1 << 26) / trg_bufsize;
-       if (hlimit < 4*BLK_SIZE)
-               hlimit = 4*BLK_SIZE;
-
-       /*
-        * Now make sure none of the hash buckets has more entries than
+        * 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++) {
-               if (hash_count[i] < hlimit)
+               if (hash_count[i] < HASH_LIMIT)
                        continue;
                entry = hash[i];
                do {
-                       struct index *keep = entry;
-                       int skip = hash_count[i] / hlimit / 2;
+                       struct index_entry *keep = entry;
+                       int skip = hash_count[i] / HASH_LIMIT / 2;
                        do {
                                entry = entry->next;
                        } while(--skip && entry);
@@ -120,31 +229,31 @@ static struct index ** delta_index(const unsigned char *buf,
        }
        free(hash_count);
 
-       return hash;
+       return index;
 }
 
-/* provide the size of the copy opcode given the block offset and size */
-#define COPYOP_SIZE(o, s) \
-    (!!(o & 0xff) + !!(o & 0xff00) + !!(o & 0xff0000) + !!(o & 0xff000000) + \
-     !!(s & 0xff) + !!(s & 0xff00) + 1)
+void free_delta_index(struct delta_index *index)
+{
+       free(index);
+}
 
-/* the maximum size for any opcode */
-#define MAX_OP_SIZE COPYOP_SIZE(0xffffffff, 0xffffffff)
+/*
+ * 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 *diff_delta(void *from_buf, unsigned long from_size,
-                void *to_buf, unsigned long to_size,
-                unsigned long *delta_size,
-                unsigned long max_size)
+void *
+create_delta(const struct delta_index *index,
+            const void *trg_buf, unsigned long trg_size,
+            unsigned long *delta_size, unsigned long max_size)
 {
-       unsigned int i, outpos, outsize, inscnt, hash_shift;
+       unsigned int i, outpos, outsize, val;
+       int inscnt;
        const unsigned char *ref_data, *ref_top, *data, *top;
        unsigned char *out;
-       struct index *entry, **hash;
 
-       if (!from_size || !to_size)
-               return NULL;
-       hash = delta_index(from_buf, from_size, to_size, &hash_shift);
-       if (!hash)
+       if (!trg_buf || !trg_size)
                return NULL;
 
        outpos = 0;
@@ -152,64 +261,66 @@ void *diff_delta(void *from_buf, unsigned long from_size,
        if (max_size && outsize >= max_size)
                outsize = max_size + MAX_OP_SIZE + 1;
        out = malloc(outsize);
-       if (!out) {
-               free(hash);
+       if (!out)
                return NULL;
-       }
-
-       ref_data = from_buf;
-       ref_top = from_buf + from_size;
-       data = to_buf;
-       top = to_buf + to_size;
 
        /* store reference buffer size */
-       out[outpos++] = from_size;
-       from_size >>= 7;
-       while (from_size) {
-               out[outpos - 1] |= 0x80;
-               out[outpos++] = from_size;
-               from_size >>= 7;
+       i = index->src_size;
+       while (i >= 0x80) {
+               out[outpos++] = i | 0x80;
+               i >>= 7;
        }
+       out[outpos++] = i;
 
        /* store target buffer size */
-       out[outpos++] = to_size;
-       to_size >>= 7;
-       while (to_size) {
-               out[outpos - 1] |= 0x80;
-               out[outpos++] = to_size;
-               to_size >>= 7;
+       i = trg_size;
+       while (i >= 0x80) {
+               out[outpos++] = i | 0x80;
+               i >>= 7;
        }
-
-       inscnt = 0;
+       out[outpos++] = i;
+
+       ref_data = index->src_buf;
+       ref_top = ref_data + index->src_size;
+       data = trg_buf;
+       top = 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;
 
        while (data < top) {
                unsigned int moff = 0, msize = 0;
-               if (data + BLK_SIZE <= top) {
-                       unsigned int val = adler32(0, data, BLK_SIZE);
-                       i = HASH(val, hash_shift);
-                       for (entry = hash[i]; entry; entry = entry->next) {
-                               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 > top - src)
-                                       ref_size = top - src;
-                               if (ref_size > 0x10000)
-                                       ref_size = 0x10000;
-                               if (ref_size <= msize)
-                                       break;
-                               while (ref_size-- && *src++ == *ref)
-                                       ref++;
-                               if (msize < ref - entry->ptr) {
-                                       /* this is our best match so far */
-                                       msize = ref - entry->ptr;
-                                       moff = entry->ptr - ref_data;
-                               }
+               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; entry = entry->next) {
+                       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 > top - src)
+                               ref_size = top - src;
+                       if (ref_size > 0x10000)
+                               ref_size = 0x10000;
+                       if (ref_size <= msize)
+                               break;
+                       while (ref_size-- && *src++ == *ref)
+                               ref++;
+                       if (msize < ref - entry->ptr) {
+                               /* this is our best match so far */
+                               msize = ref - entry->ptr;
+                               moff = entry->ptr - ref_data;
                        }
                }
 
-               if (!msize || msize < COPYOP_SIZE(moff, msize)) {
+               if (msize < 4) {
                        if (!inscnt)
                                outpos++;
                        out[outpos++] = *data++;
@@ -221,7 +332,35 @@ void *diff_delta(void *from_buf, unsigned long from_size,
                } else {
                        unsigned char *op;
 
+                       if (msize >= RABIN_WINDOW) {
+                               const unsigned char *sk;
+                               sk = data + msize - RABIN_WINDOW;
+                               val = 0;
+                               for (i = 0; i < RABIN_WINDOW; i++)
+                                       val = ((val << 8) | *sk++) ^ T[val >> RABIN_SHIFT];
+                       } else {
+                               const unsigned char *sk = data + 1;
+                               for (i = 1; i < msize; i++) {
+                                       val ^= U[sk[-RABIN_WINDOW]];
+                                       val = ((val << 8) | *sk++) ^ T[val >> RABIN_SHIFT];
+                               }
+                       }
+
                        if (inscnt) {
+                               while (moff && ref_data[moff-1] == data[-1]) {
+                                       if (msize == 0x10000)
+                                               break;
+                                       /* 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;
                        }
@@ -251,12 +390,10 @@ void *diff_delta(void *from_buf, unsigned long from_size,
                        if (max_size && outsize >= max_size)
                                outsize = max_size + MAX_OP_SIZE + 1;
                        if (max_size && outpos > max_size)
-                               out = NULL;
-                       else
-                               out = realloc(out, outsize);
+                               break;
+                       out = realloc(out, outsize);
                        if (!out) {
                                free(tmp);
-                               free(hash);
                                return NULL;
                        }
                }
@@ -265,7 +402,11 @@ void *diff_delta(void *from_buf, unsigned long from_size,
        if (inscnt)
                out[outpos - inscnt - 1] = inscnt;
 
-       free(hash);
+       if (max_size && outpos > max_size) {
+               free(out);
+               return NULL;
+       }
+
        *delta_size = outpos;
        return out;
 }