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canvas_base: Avoid misaligned access decoding LZ4 data

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Make code faster on platforms not supporting unaligned access by
default.
SPICE_UNALIGNED_CAST is just silencing possible alignment warning and,
if enabled, produces some logs, however in this case we know that the
pointer can be misaligned.
Use packed structures to tell compiler to generate best code possible.
For more details see comment on commit 74e50b57ae ("Make the
compiler work out better way to write unaligned memory").

Signed-off-by: Frediano Ziglio <fziglio@redhat.com>
Acked-by: Christophe Fergeau <cfergeau@redhat.com>
This commit is contained in:
Frediano Ziglio 2017-12-24 13:21:45 +00:00
parent 6496437e80
commit bb8d75bf31
1 changed files with 9 additions and 1 deletions
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10
common/canvas_base.c
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@ -45,6 +45,14 @@
#include "mem.h"
#include "macros.h"
#include <spice/start-packed.h>
typedef struct SPICE_ATTR_PACKED {
uint32_t v;
} uint32_unaligned_t;
#include <spice/end-packed.h>
#define read_uint32_be(ptr) ntohl(((uint32_unaligned_t *)(ptr))->v)
#define ROUND(_x) ((int)floor((_x) + 0.5))
static inline int fix_to_int(SPICE_FIXED28_4 fixed)
@ -572,7 +580,7 @@ static pixman_image_t *canvas_get_lz4(CanvasBase *canvas, SpiceImage *image)
do {
// Read next compressed block
enc_size = ntohl(*SPICE_UNALIGNED_CAST(uint32_t *, data));
enc_size = read_uint32_be(data);
data += 4;
dec_size = LZ4_decompress_safe_continue(stream, (const char *) data,
(char *) dest, enc_size, available);