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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 */
  22extern void free_delta_index(struct delta_index *index);
  23
  24/*
  25 * create_delta: create a delta from given index for the given buffer
  26 *
  27 * This function may be called multiple times with different buffers using
  28 * the same delta_index pointer.  If max_delta_size is non-zero and the
  29 * resulting delta is to be larger than max_delta_size then NULL is returned.
  30 * On success, a non-NULL pointer to the buffer with the delta data is
  31 * returned and *delta_size is updated with its size.  The returned buffer
  32 * must be freed by the caller.
  33 */
  34extern void *
  35create_delta(const struct delta_index *index,
  36             const void *buf, unsigned long bufsize,
  37             unsigned long *delta_size, unsigned long max_delta_size);
  38
  39/*
  40 * diff_delta: create a delta from source buffer to target buffer
  41 *
  42 * If max_delta_size is non-zero and the resulting delta is to be larger
  43 * than max_delta_size then NULL is returned.  On success, a non-NULL
  44 * pointer to the buffer with the delta data is returned and *delta_size is
  45 * updated with its size.  The returned buffer must be freed by the caller.
  46 */
  47static inline void *
  48diff_delta(const void *src_buf, unsigned long src_bufsize,
  49           const void *trg_buf, unsigned long trg_bufsize,
  50           unsigned long *delta_size, unsigned long max_delta_size)
  51{
  52        struct delta_index *index = create_delta_index(src_buf, src_bufsize);
  53        if (index) {
  54                void *delta = create_delta(index, trg_buf, trg_bufsize,
  55                                           delta_size, max_delta_size);
  56                free_delta_index(index);
  57                return delta;
  58        }
  59        return NULL;
  60}
  61
  62/*
  63 * patch_delta: recreate target buffer given source buffer and delta data
  64 *
  65 * On success, a non-NULL pointer to the target buffer is returned and
  66 * *trg_bufsize is updated with its size.  On failure a NULL pointer is
  67 * returned.  The returned buffer must be freed by the caller.
  68 */
  69extern void *patch_delta(const void *src_buf, unsigned long src_size,
  70                         const void *delta_buf, unsigned long delta_size,
  71                         unsigned long *dst_size);
  72
  73/* the smallest possible delta size is 4 bytes */
  74#define DELTA_SIZE_MIN  4
  75
  76/*
  77 * This must be called twice on the delta data buffer, first to get the
  78 * expected source buffer size, and again to get the target buffer size.
  79 */
  80static inline unsigned long get_delta_hdr_size(const unsigned char **datap,
  81                                               const unsigned char *top)
  82{
  83        const unsigned char *data = *datap;
  84        unsigned char cmd;
  85        unsigned long size = 0;
  86        int i = 0;
  87        do {
  88                cmd = *data++;
  89                size |= (cmd & ~0x80) << i;
  90                i += 7;
  91        } while (cmd & 0x80 && data < top);
  92        *datap = data;
  93        return size;
  94}
  95
  96#endif