First adjusted some typos in comments inside the function. Second,
change the naming of some variable to reduce confusion.
A special case has been inserted when advance is done inside a GAP block
and this block is the last of the buffer. In this case, the whole buffer
will be emptied, equivalent to a ncb_init() operation.
A new function ncb_advance() is implemented. This is used to advance the
buffer head pointer. This will consume the front data while forming a
new gap at the end for future data.
On success NCB_RET_OK is returned. The operation can be rejected if a
too small new gap is formed in front of the buffer.
Define three different ways to proceed insertion. This configures how
overlapping data is treated.
- NCB_ADD_PRESERVE : in this mode, old data are kept during insertion.
- NCB_ADD_OVERWRT : new data will overwrite old ones.
- NCB_ADD_COMPARE : this mode adds a new test in check stage. The
overlapping old and new data must be identical or else the insertion
is not conducted. An error NCB_RET_DATA_REJ is used in this case.
The mode is specified with a new argument to ncb_add() function.
Implement a new function ncb_add() to insert data in ncbuf. This
operation is conducted in two stages. First, a simulation will be run to
ensure that insertion can be proceeded. If a gap is formed, either
before or after the new data, it must be big enough to store its header,
or else the insertion is aborted.
After this check stage, the insertion is conducted block by block with
the function pair ncb_fill_data_blk()/ncb_fill_gap_blk().
A new type ncb_ret is used as a return value. For the moment, only
success or gap-size error is used. It is planned to add new error types
in the future when insertion will be extended.
Implement two new functions to report the total data stored accross the
whole buffer and the data stored at a specific offset until the next gap
or the buffer end.
To facilitate implementation of these new functions and also future
add/delete operations, a new abstraction is introduced : ncb_blk. This
structure represents a block of either data or gap in the buffer. It
simplifies operation when moving forward in the buffer. The first buffer
block can be retrieved via ncb_blk_first(buf). The block at a specific
offset is accessed via ncb_blk_find(buf, off).
This abstraction is purely used in functions but not stored in the ncbuf
structure per-se. This is necessary to keep the minimal memory
footprint.
Define the new type ncbuf. It can be used as a buffer with
non-contiguous data and wrapping support.
To reduce as much as possible the memory footprint, size of data and
gaps are stored in the gaps themselves. This put some limitation on the
buffer usage. A reserved space is present just before the head to store
the size of the first data block. Also, add and delete operations will
be constrained to ensure minimal gap sizes are preserved.
The sizes stored in the gaps are represented by a custom type named
ncb_sz_t. This type is a typedef to easily change it : this has a
direct impact on the maximum buffer size (MAX(ncb_sz_t) - sizeof(ncb_sz_t))
and the minimal gap sizes (sizeof(ncb_sz_t) * 2)).
Currently, it is set to uint32_t.
