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buffering: leave a comment to explain what is broken in the code and link to FS#10605

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git-svn-id: svn://svn.rockbox.org/rockbox/trunk@23344 a1c6a512-1295-4272-9138-f99709370657
This commit is contained in:
Rafaël Carré 2009-10-25 11:03:59 +00:00
parent 0b302f0cb9
commit f3944cb694
1 changed files with 25 additions and 0 deletions
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25
apps/buffering.c
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@ -486,6 +486,31 @@ static bool move_handle(struct memory_handle **h, size_t *delta,
cur_handle = dest;
if (overlap > 0) {
/* FIXME : this code is broken and can leave the data corrupted when
* the amount of data to move is close to the whole buffer size.
*
* Example : ('S' is the source data, '-' is empty buffer)
* Size of the buffer is 8 bytes, starts at 0.
* Size of the data to move is 7 bytes.
*
* -SSSSSSS
* ^-------- start of source data == 1
*
* DD-DDDDD ('D' is desired destination data)
* ^------ start of destination data == 3
*
* memmove(3, 1, 5);
* memmove(0, 7, 2);
*
* First memmove() call will leave the buffer in this state:
*
* -SSDDDDD
* ^^
* \--- data to be moved by the second memmove() call, but
* overwritten by the first call.
*
* See FS#10605 for more details
*/
size_t first_part = size_to_move - overlap;
memmove(dest, src, first_part);
memmove(buffer, (const char *)src + first_part, overlap);