split the diff-delta interface

This patch splits the diff-delta interface into index creation and delta
generation.  A wrapper is provided to preserve the diff-delta() call.

This will allow for an optimization in pack-objects.c where the source
object could be fixed and a full window of objects tentatively tried
against
that same source object without recomputing the source index each time.

This patch only restructure things, plus a couple cleanups for good
measure. There is no performance change yet.

Signed-off-by: Nicolas Pitre <nico@cam.org>

diff --git a/delta.h b/delta.h
index 9464f3e9b08b959d11305688ce194867a4017817..727ae30e9eb973b2bd4a512be78041fee40fa039 100644 (file)
--- a/delta.h
+++ b/delta.h
@@ -1,12 +1,73 @@
 #ifndef DELTA_H
 #define DELTA_H
 
-/* handling of delta buffers */
-extern 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);
-extern void *patch_delta(void *src_buf, unsigned long src_size,
-                        void *delta_buf, unsigned long delta_size,
+/* opaque object for delta index */
+struct 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 delta_index *
+create_delta_index(const void *buf, unsigned long bufsize);
+
+/*
+ * free_delta_index: free the index created by create_delta_index()
+ */
+extern void free_delta_index(struct 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 *
+create_delta(const struct 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.
+ */
+static inline void *
+diff_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 delta_index *index = create_delta_index(src_buf, src_bufsize);
+       if (index) {
+               void *delta = create_delta(index, trg_buf, trg_bufsize,
+                                          delta_size, max_delta_size);
+               free_delta_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 *patch_delta(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 */
@@ -14,7 +75,7 @@ extern void *patch_delta(void *src_buf, unsigned long src_size,
 
 /*
  * This must be called twice on the delta data buffer, first to get the
- * expected reference buffer size, and again to get the result buffer size.
+ * expected source buffer size, and again to get the target buffer size.
  */
 static inline unsigned long get_delta_hdr_size(const unsigned char **datap,
                                               const unsigned char *top)

diff --git a/diff-delta.c b/diff-delta.c
index 1188b31cd0f1e2f3a1fc2096a10243a03b439021..fdedf94ccec935732a5234708557f7810b5b8bfd 100644 (file)
--- a/diff-delta.c
+++ b/diff-delta.c
@@ -27,53 +27,70 @@
 /* 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 GR_PRIME 0x9e370001
 #define HASH(v, shift) (((unsigned int)(v) * GR_PRIME) >> (shift))
 
-struct index {
+struct index_entry {
        const unsigned char *ptr;
        unsigned int val;
-       struct index *next;
+       struct index_entry *next;
 };
 
-static struct index ** delta_index(const unsigned char *buf,
-                                  unsigned long bufsize,
-                                  unsigned long trg_bufsize,
-                                  unsigned int *hash_shift)
+struct delta_index {
+       const void *src_buf;
+       unsigned long src_size;
+       unsigned int hash_shift;
+       struct index_entry *hash[0];
+};
+
+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, hshift, entries, *hash_count;
+       const unsigned char *data, *buffer = buf;
+       struct delta_index *index;
+       struct index_entry *entry, **hash;
        void *mem;
 
+       if (!buf || !bufsize)
+               return NULL;
+
        /* determine index hash size */
        entries = bufsize  / BLK_SIZE;
        hsize = entries / 4;
        for (i = 4; (1 << i) < hsize && i < 31; i++);
        hsize = 1 << i;
        hshift = 32 - i;
-       *hash_shift = hshift;
 
        /* allocate lookup index */
-       mem = malloc(hsize * sizeof(*hash) + entries * sizeof(*entry));
+       mem = malloc(sizeof(*index) +
+                    sizeof(*hash) * hsize +
+                    sizeof(*entry) * entries);
        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_shift = hshift;
        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) {
+       data = buffer + entries * BLK_SIZE - BLK_SIZE;
+       while (data >= buffer) {
                unsigned int val = adler32(0, data, BLK_SIZE);
                i = HASH(val, hshift);
                entry->ptr = data;
@@ -91,27 +108,18 @@ 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);
@@ -120,7 +128,12 @@ static struct index ** delta_index(const unsigned char *buf,
        }
        free(hash_count);
 
-       return hash;
+       return index;
+}
+
+void free_delta_index(struct delta_index *index)
+{
+       free(index);
 }
 
 /* provide the size of the copy opcode given the block offset and size */
@@ -131,21 +144,17 @@ static struct index ** delta_index(const unsigned char *buf,
 /* the maximum size for any opcode */
 #define MAX_OP_SIZE COPYOP_SIZE(0xffffffff, 0xffffffff)
 
-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, hash_shift;
        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;
@@ -153,60 +162,55 @@ 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;
        }
+       out[outpos++] = i;
 
+       ref_data = index->src_buf;
+       ref_top = ref_data + index->src_size;
+       data = trg_buf;
+       top = trg_buf + trg_size;
+       hash_shift = index->hash_shift;
        inscnt = 0;
 
        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;
+               unsigned int val = adler32(0, data, BLK_SIZE);
+               i = HASH(val, hash_shift);
+               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;
                        }
                }
 
@@ -271,7 +275,6 @@ void *diff_delta(void *from_buf, unsigned long from_size,
                                out = realloc(out, outsize);
                        if (!out) {
                                free(tmp);
-                               free(hash);
                                return NULL;
                        }
                }
@@ -280,7 +283,6 @@ void *diff_delta(void *from_buf, unsigned long from_size,
        if (inscnt)
                out[outpos - inscnt - 1] = inscnt;
 
-       free(hash);
        *delta_size = outpos;
        return out;
 }

diff --git a/patch-delta.c b/patch-delta.c
index d95f0d9721dd87c0d4aff485e32e0a68623ee5cc..8f318ed8aaf180419f97887501317fc1d2b54c09 100644 (file)
--- a/patch-delta.c
+++ b/patch-delta.c
@@ -13,8 +13,8 @@
 #include <string.h>
 #include "delta.h"
 
-void *patch_delta(void *src_buf, unsigned long src_size,
-                 void *delta_buf, unsigned long delta_size,
+void *patch_delta(const void *src_buf, unsigned long src_size,
+                 const void *delta_buf, unsigned long delta_size,
                  unsigned long *dst_size)
 {
        const unsigned char *data, *top;