Rockbox open source high quality audio player as a Music Player Daemon
mpris
rockbox
mpd
libadwaita
audio
rust
zig
deno
buflib: optimize getting start of block from end of block
The block header has a variable length due to the embedded name.
The name length is stored at the back of the header after the
name, in order to allow finding the start of the header if only
the user data pointer is known (eg. from the handle table).
The name length is actually not interesting in itself; storing
the total length of the block header instead is marginally more
efficient, saving one addition in handle_to_block().
Instead the extra arithmetic must be done by buflib_get_name(),
which is a much less common operation than handle_to_block().
Change-Id: Ia339a1d2f556a11a49deae0871203e70548bd234
+12
-10
+12
-10
firmware/buflib.c
+12
-10
firmware/buflib.c
···
65
65
* H - handle table entry pointer
66
66
* C - pointer to struct buflib_callbacks
67
67
* c - variable sized string identifier
68
-
* L2 - second length marker for string identifier
68
+
* L2 - length of the metadata
69
69
* crc - crc32 protecting buflib metadata integrity
70
70
* X - actual payload
71
71
* Y - unallocated space
···
240
240
* has already been allocated but not the data */
241
241
if (!data)
242
242
return NULL;
243
-
volatile size_t len = data[-2].val;
244
-
return data - (len + 4);
243
+
244
+
return data - data[-2].val;
245
245
}
246
246
247
247
/* Shrink the handle table, returning true if its size was reduced, false if
···
627
627
/* Set up the allocated block, by marking the size allocated, and storing
628
628
* a pointer to the handle.
629
629
*/
630
-
union buflib_data *name_len_slot, *crc_slot;
630
+
union buflib_data *header_size_slot, *crc_slot;
631
631
block->val = size;
632
632
block[1].handle = handle;
633
633
block[2].ops = ops;
634
634
if (name_len > 0)
635
635
strcpy(block[3].name, name);
636
-
name_len_slot = (union buflib_data*)B_ALIGN_UP(block[3].name + name_len);
637
-
name_len_slot->val = 1 + name_len/sizeof(union buflib_data);
638
-
crc_slot = (union buflib_data*)(name_len_slot + 1);
636
+
header_size_slot = (union buflib_data*)B_ALIGN_UP(block[3].name + name_len);
637
+
header_size_slot->val = 5 + name_len/sizeof(union buflib_data);
638
+
crc_slot = (union buflib_data*)(header_size_slot + 1);
639
639
crc_slot->crc = crc_32((void *)block,
640
640
(crc_slot - block)*sizeof(union buflib_data),
641
641
0xffffffff);
···
742
742
free_space_at_end(struct buflib_context* ctx)
743
743
{
744
744
/* subtract 5 elements for
745
-
* val, handle, name_len, ops and the handle table entry*/
745
+
* val, handle, meta_len, ops and the handle table entry*/
746
746
ptrdiff_t diff = (ctx->last_handle - ctx->alloc_end - 5);
747
747
diff -= 16; /* space for future handles */
748
748
diff *= sizeof(union buflib_data); /* make it bytes */
···
933
933
{
934
934
union buflib_data *data = ALIGN_DOWN(buflib_get_data(ctx, handle), sizeof (*data));
935
935
size_t len = data[-2].val;
936
-
if (len <= 1)
936
+
if (len <= 5)
937
937
return NULL;
938
-
return data[-len-1].name;
938
+
939
+
data -= len;
940
+
return data[3].name;
939
941
}
940
942
941
943
#ifdef DEBUG