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   1#ifndef DELTA_H
   2#define DELTA_H
   3
   4/* opaque object for delta index */
   5struct delta_index;
   6
   7/*
   8 * create_delta_index: compute index data from given buffer
   9 *
  10 * This returns a pointer to a struct delta_index that should be passed to
  11 * subsequent create_delta() calls, or to free_delta_index().  A NULL pointer
  12 * is returned on failure.  The given buffer must not be freed nor altered
  13 * before free_delta_index() is called.  The returned pointer must be freed
  14 * using free_delta_index().
  15 */
  16extern struct delta_index *
  17create_delta_index(const void *buf, unsigned long bufsize);
  18
  19/*
  20 * free_delta_index: free the index created by create_delta_index()
  21 *
  22 * Given pointer must be what create_delta_index() returned, or NULL.
  23 */
  24extern void free_delta_index(struct delta_index *index);
  25
  26/*
  27 * create_delta: create a delta from given index for the given buffer
  28 *
  29 * This function may be called multiple times with different buffers using
  30 * the same delta_index pointer.  If max_delta_size is non-zero and the
  31 * resulting delta is to be larger than max_delta_size then NULL is returned.
  32 * On success, a non-NULL pointer to the buffer with the delta data is
  33 * returned and *delta_size is updated with its size.  The returned buffer
  34 * must be freed by the caller.
  35 */
  36extern void *
  37create_delta(const struct delta_index *index,
  38             const void *buf, unsigned long bufsize,
  39             unsigned long *delta_size, unsigned long max_delta_size);
  40
  41/*
  42 * diff_delta: create a delta from source buffer to target buffer
  43 *
  44 * If max_delta_size is non-zero and the resulting delta is to be larger
  45 * than max_delta_size then NULL is returned.  On success, a non-NULL
  46 * pointer to the buffer with the delta data is returned and *delta_size is
  47 * updated with its size.  The returned buffer must be freed by the caller.
  48 */
  49static inline void *
  50diff_delta(const void *src_buf, unsigned long src_bufsize,
  51           const void *trg_buf, unsigned long trg_bufsize,
  52           unsigned long *delta_size, unsigned long max_delta_size)
  53{
  54        struct delta_index *index = create_delta_index(src_buf, src_bufsize);
  55        if (index) {
  56                void *delta = create_delta(index, trg_buf, trg_bufsize,
  57                                           delta_size, max_delta_size);
  58                free_delta_index(index);
  59                return delta;
  60        }
  61        return NULL;
  62}
  63
  64/*
  65 * patch_delta: recreate target buffer given source buffer and delta data
  66 *
  67 * On success, a non-NULL pointer to the target buffer is returned and
  68 * *trg_bufsize is updated with its size.  On failure a NULL pointer is
  69 * returned.  The returned buffer must be freed by the caller.
  70 */
  71extern void *patch_delta(const void *src_buf, unsigned long src_size,
  72                         const void *delta_buf, unsigned long delta_size,
  73                         unsigned long *dst_size);
  74
  75/* the smallest possible delta size is 4 bytes */
  76#define DELTA_SIZE_MIN  4
  77
  78/*
  79 * This must be called twice on the delta data buffer, first to get the
  80 * expected source buffer size, and again to get the target buffer size.
  81 */
  82static inline unsigned long get_delta_hdr_size(const unsigned char **datap,
  83                                               const unsigned char *top)
  84{
  85        const unsigned char *data = *datap;
  86        unsigned char cmd;
  87        unsigned long size = 0;
  88        int i = 0;
  89        do {
  90                cmd = *data++;
  91                size |= (cmd & ~0x80) << i;
  92                i += 7;
  93        } while (cmd & 0x80 && data < top);
  94        *datap = data;
  95        return size;
  96}
  97
  98#endif