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h264: refactor NAL decode loop

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Write out the NAL decoding loops in full so that they are easier
to parse for a preprocessor without it having to be aware of macros
or other such things in C code.

This also makes the code more readable.

Signed-off-by: Luca Barbato <lu_zero@gentoo.org>
This commit is contained in:
Ronald S. Bultje 2012-07-22 20:46:10 -07:00 committed by Luca Barbato
parent 08cd95e8a3
commit 58db34aa1e
1 changed files with 25 additions and 17 deletions
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42
libavcodec/h264.c
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@ -175,42 +175,50 @@ const uint8_t *ff_h264_decode_nal(H264Context *h, const uint8_t *src,
src++; src++;
length--; length--;
#define STARTCODE_TEST \
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 #if HAVE_FAST_UNALIGNED
#define FIND_FIRST_ZERO \
if (i > 0 && !src[i]) \
i--; \
while (src[i]) \
i++
#if HAVE_FAST_64BIT #if HAVE_FAST_64BIT
#define RS 7
for (i = 0; i + 1 < length; i += 9) { for (i = 0; i + 1 < length; i += 9) {
if (!((~AV_RN64A(src + i) & if (!((~AV_RN64A(src + i) &
(AV_RN64A(src + i) - 0x0100010001000101ULL)) & (AV_RN64A(src + i) - 0x0100010001000101ULL)) &
0x8000800080008080ULL)) 0x8000800080008080ULL))
continue;
FIND_FIRST_ZERO;
STARTCODE_TEST;
i -= 7;
}
#else #else
#define RS 3
for (i = 0; i + 1 < length; i += 5) { for (i = 0; i + 1 < length; i += 5) {
if (!((~AV_RN32A(src + i) & if (!((~AV_RN32A(src + i) &
(AV_RN32A(src + i) - 0x01000101U)) & (AV_RN32A(src + i) - 0x01000101U)) &
0x80008080U)) 0x80008080U))
#endif
continue; continue;
if (i > 0 && !src[i]) FIND_FIRST_ZERO;
i--; STARTCODE_TEST;
while (src[i]) i -= 3;
i++; }
#endif
#else #else
#define RS 0
for (i = 0; i + 1 < length; i += 2) { for (i = 0; i + 1 < length; i += 2) {
if (src[i]) if (src[i])
continue; continue;
if (i > 0 && src[i - 1] == 0) if (i > 0 && src[i - 1] == 0)
i--; i--;
#endif STARTCODE_TEST;
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;
}
i -= RS;
} }
#endif
if (i >= length - 1) { // no escaped 0 if (i >= length - 1) { // no escaped 0
*dst_length = length; *dst_length = length;