Hi,
On Sat, Jul 21, 2012 at 5:19 PM, Måns Rullgård <m...@mansr.com> wrote:
> "Ronald S. Bultje" <rsbul...@gmail.com> writes:
>
>> From: "Ronald S. Bultje" <rsbul...@gmail.com>
>>
>> This removes some code duplication between the 3 different versions,
>> and aligns brackets in such a way that it is now possible to pull
>> this code through a naive pre-processor that doesn't necessarily have
>> to be aware of compiler-macros.
>> ---
>> libavcodec/h264.c | 36 ++++++++++++++++++++----------------
>> 1 file changed, 20 insertions(+), 16 deletions(-)
>>
>> diff --git a/libavcodec/h264.c b/libavcodec/h264.c
>> index a4afcc8..20fa7c3 100644
>> --- a/libavcodec/h264.c
>> +++ b/libavcodec/h264.c
>> @@ -178,30 +178,34 @@ const uint8_t *ff_h264_decode_nal(H264Context *h,
>> const uint8_t *src,
>> #if HAVE_FAST_UNALIGNED
>> #if HAVE_FAST_64BIT
>> #define RS 7
>> - for (i = 0; i + 1 < length; i += 9) {
>> - if (!((~AV_RN64A(src + i) &
>> - (AV_RN64A(src + i) - 0x0100010001000101ULL)) &
>> +#define MASKCHECK \
>> + if (!((~AV_RN64A(src + i) & \
>> + (AV_RN64A(src + i) - 0x0100010001000101ULL)) & \
>> 0x8000800080008080ULL))
>> #else
>> #define RS 3
>> - for (i = 0; i + 1 < length; i += 5) {
>> - if (!((~AV_RN32A(src + i) &
>> - (AV_RN32A(src + i) - 0x01000101U)) &
>> +#define MASKCHECK \
>> + if (!((~AV_RN32A(src + i) & \
>> + (AV_RN32A(src + i) - 0x01000101U)) & \
>> 0x80008080U))
>> #endif
>> - continue;
>> - if (i > 0 && !src[i])
>> - i--;
>> - while (src[i])
>> - i++;
>> +#define LOOPCHECK \
>> + MASKCHECK \
>> + continue; \
>> + if (i > 0 && !src[i]) \
>> + i--; \
>> + while (src[i]) \
>> + i++
>> #else
>> #define RS 0
>> - for (i = 0; i + 1 < length; i += 2) {
>> - if (src[i])
>> - continue;
>> - if (i > 0 && src[i - 1] == 0)
>> - i--;
>> +#define LOOPCHECK \
>> + if (src[i]) \
>> + continue; \
>> + if (i > 0 && src[i - 1] == 0) \
>> + i--
>> #endif
>> + for (i = 0; i + 1 < length; i += RS + 2) {
>> + LOOPCHECK;
>> if (i + 2 < length && src[i + 1] == 0 && src[i + 2] <= 3) {
>> if (src[i + 2] != 3) {
>> /* startcode, so we must be past the end */
>> --
>
> This manner of splitting things is incredibly weird-looking. Instead of
> trying to unify these rather different fragments, turning the second
> half of the loop into a macro and writing out separate loops, each
> calling the macro for the common part, would probably look much more
> sane.
#define LOOP_COMMON_PART \
if (i + 2 < length && src[i + 1] == 0 && src[i + 2] <= 3) { \
if (src[i + 2] != 3) { \
/* startcode, so we must be past the end */ \
length = i; \
} \
break; \
}
#if HAVE_FAST_UNALIGNED
#define CHECK_COMMON_PART \
if (i > 0 && !src[i]) \
i--; \
while (src[i]) \
i++
#if HAVE_FAST_64BIT
for (i = 0; i + 1 < length; i += 9) {
if (!((~AV_RN64A(src + i) &
(AV_RN64A(src + i) - 0x0100010001000101ULL)) &
0x8000800080008080ULL))
continue;
CHECK_COMMON_PART;
LOOP_COMMON_PART;
i -= 7;
}
#else
for (i = 0; i + 1 < length; i += 5) {
if (!((~AV_RN32A(src + i) &
(AV_RN32A(src + i) - 0x01000101U)) &
0x80008080U))
continue;
CHECK_COMMON_PART;
LOOP_COMMON_PART;
i -= 3;
}
#endif
#else
for (i = 0; i + 1 < length; i += 2) {
if (src[i])
continue;
if (i > 0 && src[i - 1] == 0)
i--;
LOOP_COMMON_PART;
}
#endif
Pick your bet and commit whichever is nicer; both work with the
preprocessor. (I think the earlier one looks better.)
Ronald
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