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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 or altered
  13 * before free_delta_index() is called.  The returned pointer must be freed
  14 * using free_delta_index().
  15 */
  16struct 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 */
  24void free_delta_index(struct delta_index *index);
  25
  26/*
  27 * sizeof_delta_index: returns memory usage of delta index
  28 *
  29 * Given pointer must be what create_delta_index() returned, or NULL.
  30 */
  31unsigned long sizeof_delta_index(struct delta_index *index);
  32
  33/*
  34 * create_delta: create a delta from given index for the given buffer
  35 *
  36 * This function may be called multiple times with different buffers using
  37 * the same delta_index pointer.  If max_delta_size is non-zero and the
  38 * resulting delta is to be larger than max_delta_size then NULL is returned.
  39 * On success, a non-NULL pointer to the buffer with the delta data is
  40 * returned and *delta_size is updated with its size.  The returned buffer
  41 * must be freed by the caller.
  42 */
  43void *
  44create_delta(const struct delta_index *index,
  45             const void *buf, unsigned long bufsize,
  46             unsigned long *delta_size, unsigned long max_delta_size);
  47
  48/*
  49 * diff_delta: create a delta from source buffer to target buffer
  50 *
  51 * If max_delta_size is non-zero and the resulting delta is to be larger
  52 * than max_delta_size then NULL is returned.  On success, a non-NULL
  53 * pointer to the buffer with the delta data is returned and *delta_size is
  54 * updated with its size.  The returned buffer must be freed by the caller.
  55 */
  56static inline void *
  57diff_delta(const void *src_buf, unsigned long src_bufsize,
  58           const void *trg_buf, unsigned long trg_bufsize,
  59           unsigned long *delta_size, unsigned long max_delta_size)
  60{
  61        struct delta_index *index = create_delta_index(src_buf, src_bufsize);
  62        if (index) {
  63                void *delta = create_delta(index, trg_buf, trg_bufsize,
  64                                           delta_size, max_delta_size);
  65                free_delta_index(index);
  66                return delta;
  67        }
  68        return NULL;
  69}
  70
  71/*
  72 * patch_delta: recreate target buffer given source buffer and delta data
  73 *
  74 * On success, a non-NULL pointer to the target buffer is returned and
  75 * *trg_bufsize is updated with its size.  On failure a NULL pointer is
  76 * returned.  The returned buffer must be freed by the caller.
  77 */
  78void *patch_delta(const void *src_buf, unsigned long src_size,
  79                  const void *delta_buf, unsigned long delta_size,
  80                  unsigned long *dst_size);
  81
  82/* the smallest possible delta size is 4 bytes */
  83#define DELTA_SIZE_MIN  4
  84
  85/*
  86 * This must be called twice on the delta data buffer, first to get the
  87 * expected source buffer size, and again to get the target buffer size.
  88 */
  89static inline unsigned long get_delta_hdr_size(const unsigned char **datap,
  90                                               const unsigned char *top)
  91{
  92        const unsigned char *data = *datap;
  93        unsigned long cmd, size = 0;
  94        int i = 0;
  95        do {
  96                cmd = *data++;
  97                size |= (cmd & 0x7f) << i;
  98                i += 7;
  99        } while (cmd & 0x80 && data < top);
 100        *datap = data;
 101        return size;
 102}
 103
 104#endif