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Add av_memcpy_backptr(): deliberately overlapping memcpy variant. 

Originally committed as revision 14641 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Peter Ross 2008-08-06 08:17:03 +00:00
parent c0f0b34bba
commit 6ba10f338a
2 changed files with 23 additions and 3 deletions
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24
libavutil/lzo.c
View File

@ -106,6 +106,8 @@ static inline void copy(LZOContext *c, int cnt) {
c->out = dst + cnt;
}
static inline void memcpy_backptr(uint8_t *dst, int back, int cnt);
/**
* \brief copy previously decoded bytes to current position
* \param back how many bytes back we start
@ -125,9 +127,14 @@ static inline void copy_backptr(LZOContext *c, int back, int cnt) {
cnt = FFMAX(c->out_end - dst, 0);
c->error |= LZO_OUTPUT_FULL;
}
memcpy_backptr(dst, back, cnt);
c->out = dst + cnt;
}
static inline void memcpy_backptr(uint8_t *dst, int back, int cnt) {
const uint8_t *src = &dst[-back];
if (back == 1) {
memset(dst, *src, cnt);
dst += cnt;
} else {
#ifdef OUTBUF_PADDED
COPY2(dst, src);
@ -155,9 +162,20 @@ static inline void copy_backptr(LZOContext *c, int back, int cnt) {
}
memcpy(dst, src, cnt);
}
dst += cnt;
}
c->out = dst;
}
/**
* \brief deliberately overlapping memcpy implementation
* \param dst destination buffer; must be padded with 12 additional bytes
* \param back how many bytes back we start (the initial size of the overlapping window)
* \param cnt number of bytes to copy, must be >= 0
*
* cnt > back is valid, this will copy the bytes we just copied,
* thus creating a repeating pattern with a period length of back.
*/
void av_memcpy_backptr(uint8_t *dst, int back, int cnt) {
memcpy_backptr(dst, back, cnt);
}
/**

2
libavutil/lzo.h
View File

@ -32,4 +32,6 @@
int lzo1x_decode(void *out, int *outlen, const void *in, int *inlen);
void av_memcpy_backptr(uint8_t *dst, int back, int cnt);
#endif /* FFMPEG_LZO_H */