From 6ba10f338ae8fe06faa1ed830ce07ce036cc2fdc Mon Sep 17 00:00:00 2001
From: Peter Ross <pross@xvid.org>
Date: Wed, 6 Aug 2008 08:17:03 +0000
Subject: [PATCH] Add av_memcpy_backptr(): deliberately overlapping memcpy
variant.
Originally committed as revision 14641 to svn://svn.ffmpeg.org/ffmpeg/trunk
---
libavutil/lzo.c | 24 +++++++++++++++++++++---
libavutil/lzo.h | 2 ++
2 files changed, 23 insertions(+), 3 deletions(-)
diff --git a/libavutil/lzo.c b/libavutil/lzo.c
index d5d11867f80..12d3b894b50 100644
--- a/libavutil/lzo.c
+++ b/libavutil/lzo.c
@@ -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);
}
/**
diff --git a/libavutil/lzo.h b/libavutil/lzo.h
index e7795f7718e..6c5e5a31bcb 100644
--- a/libavutil/lzo.h
+++ b/libavutil/lzo.h
@@ -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 */
--
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