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Improve move_handle's semantics. Shoudl have no functional impact

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git-svn-id: svn://svn.rockbox.org/rockbox/trunk@15351 a1c6a512-1295-4272-9138-f99709370657
This commit is contained in:
Brandon Low 2007-10-28 20:18:59 +00:00
parent 94b133ad33
commit 4feab10a0c
1 changed files with 37 additions and 25 deletions
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62
apps/buffering.c
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@ -377,37 +377,43 @@ static struct memory_handle *find_handle(const unsigned int handle_id)
return m;
}
/* Move a memory handle and data_size of its data of delta.
Return a pointer to the new location of the handle (null if it hasn't moved).
delta is the value of which to move the struct data, modified to the actual
distance moved.
data_size is the amount of data to move along with the struct. */
/* Move a memory handle and data_size of its data delta bytes along the buffer.
delta maximum bytes available to move the handle. If the move is performed
it is set to the actual distance moved.
data_size is the amount of data to move along with the struct.
returns a valid memory_handle if the move is successful
NULL if the handle is NULL, the move would be less than the size of
a memory_handle after correcting for wraps or if the handle is not
found in the linked list for adjustment. This function has no side
effects if NULL is returned. */
static struct memory_handle *move_handle(const struct memory_handle *h,
size_t *delta, const size_t data_size)
{
struct memory_handle *dest;
size_t newpos;
size_t size_to_move;
size_t new_delta = *delta;
int overlap;
if (*delta < sizeof(struct memory_handle)) {
/* It's not worth trying to move such a short distance, and it would
* complicate the overlap calculations below */
if (h == NULL)
return NULL;
size_to_move = sizeof(struct memory_handle) + data_size;
/* Align to four bytes, down */
new_delta &= ~3;
if (new_delta < sizeof(struct memory_handle)) {
/* It's not legal to move less than the size of the struct */
return NULL;
}
mutex_lock(&llist_mutex);
size_to_move = sizeof(struct memory_handle) + data_size;
/* Align to four bytes, down */
*delta &= ~3;
newpos = RINGBUF_ADD((void *)h - (void *)buffer, *delta);
newpos = RINGBUF_ADD((void *)h - (void *)buffer, new_delta);
overlap = RINGBUF_ADD_CROSS(newpos, size_to_move, buffer_len - 1);
/* This means that moving the data will put it on the wrap */
if (overlap > 0) {
/* This means that the memory_handle struct would wrap */
/* Some part of the struct + data would wrap, maybe ok */
size_t correction;
/* If the overlap lands inside the memory_handle */
if ((unsigned)overlap > data_size) {
@ -415,19 +421,22 @@ static struct memory_handle *move_handle(const struct memory_handle *h,
* wrapping, this guarantees an aligned delta, I think */
correction = overlap - data_size;
} else {
/* Otherwise it falls in the data area and must all be backed out */
/* Otherwise the overlap falls in the data area and must all be
* backed out. This may become conditional if ever we move
* data that is allowed to wrap (ie audio) */
correction = overlap;
/* Align to four bytes, up */
/* Align correction to four bytes, up */
correction = (correction+3) & ~3;
if (*delta <= correction) {
/* After correcting, no movement (or, impossibly, backwards) */
mutex_unlock(&llist_mutex);
return NULL;
}
}
if (new_delta < correction + sizeof(struct memory_handle)) {
/* Delta cannot end up less than the size of the struct */
mutex_unlock(&llist_mutex);
return NULL;
}
newpos -= correction;
overlap -= correction;
*delta -= correction;
overlap -= correction; /* Used below to know how to split the data */
new_delta -= correction;
}
dest = (struct memory_handle *)(&buffer[newpos]);
@ -440,7 +449,7 @@ static struct memory_handle *move_handle(const struct memory_handle *h,
while (m && m->next != h) {
m = m->next;
}
if (h && m && m->next == h) {
if (m && m->next == h) {
m->next = dest;
} else {
mutex_unlock(&llist_mutex);
@ -448,6 +457,9 @@ static struct memory_handle *move_handle(const struct memory_handle *h,
}
}
/* All checks pass, update the caller with how far we're moving */
*delta = new_delta;
/* Update the cache to prevent it from keeping the old location of h */
if (h == cached_handle)
cached_handle = dest;