[Ffmpeg-devel] [PATCH] simple internal lzo decoder

Reimar Döffinger Reimar.Doeffinger
Sun Jan 15 18:27:55 CET 2006


Hi,
On Sat, Jan 14, 2006 at 04:21:44PM +0100, Reimar D?ffinger wrote:
> Also instead of the last patch I'd like to propose the attached one,

A last try, the speed is really nice (though only tested on my system).
But it needs a bit of padding for the buffers - since it is done in
other place I guess this is okay even if I personally don't like it
much.
Ok, here are the values: first comes liblzo, then minilzo and then this
implementation with the patch. And then the same but for gcc 4.0.0 (I
know, outdated, but that's what I had).

file all zeroes, 56325B comp:
8.90 8.90 0.80 8.87 8.46 0.75

nwnmod, 2675408B comp:
7.39 6.98 6.87 7.35 7.18 6.39

/dev/urandom, 10527740B comp:
4.28 4.13 1.72 4.28 4.24 1.73

Oh, and the image of my RE drawing is up as well :-) :
http://www.stud.uni-karlsruhe.de/~uvhe/LZODraw_bw.png

Greetings,
Reimar D?ffinger
-------------- next part --------------
Index: libavcodec/cscd.c
===================================================================
RCS file: /cvsroot/ffmpeg/ffmpeg/libavcodec/cscd.c,v
retrieving revision 1.3
diff -u -r1.3 cscd.c
--- libavcodec/cscd.c	12 Jan 2006 22:43:14 -0000	1.3
+++ libavcodec/cscd.c	15 Jan 2006 17:17:11 -0000
@@ -232,7 +232,7 @@
     c->linelen = avctx->width * avctx->bits_per_sample / 8;
     c->height = avctx->height;
     c->decomp_size = c->height * c->linelen;
-    c->decomp_buf = av_malloc(c->decomp_size);
+    c->decomp_buf = av_malloc(c->decomp_size + LZO_OUTPUT_PADDING);
     if (!c->decomp_buf) {
         av_log(avctx, AV_LOG_ERROR, "Can't allocate decompression buffer.\n");
         return 1;
Index: libavcodec/lzo.c
===================================================================
RCS file: /cvsroot/ffmpeg/ffmpeg/libavcodec/lzo.c,v
retrieving revision 1.4
diff -u -r1.4 lzo.c
--- libavcodec/lzo.c	14 Jan 2006 14:59:11 -0000	1.4
+++ libavcodec/lzo.c	15 Jan 2006 17:17:15 -0000
@@ -17,12 +17,18 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 #include "common.h"
+//! avoid e.g. MPlayers fast_memcpy, it slows things down here
+#undef memcpy
+#include <string.h>
 #include "lzo.h"
 
+//! define if we may write up to 12 bytes beyond the output buffer
+#define OUTBUF_PADDED 1
+//! define if we may read up to 4 bytes beyond the input buffer
+#define INBUF_PADDED 1
 typedef struct LZOContext {
     uint8_t *in, *in_end;
-    uint8_t *out, *out_end;
-    int out_size;
+    uint8_t *out_start, *out, *out_end;
     int error;
 } LZOContext;
 
@@ -57,17 +63,29 @@
  * \param cnt number of bytes to copy, must be > 0
  */
 static inline void copy(LZOContext *c, int cnt) {
-    if (c->in + cnt > c->in_end) {
-        cnt = c->in_end - c->in;
+    register uint8_t *src = c->in;
+    register uint8_t *dst = c->out;
+    if (src + cnt > c->in_end) {
+        cnt = c->in_end - src;
         c->error |= LZO_INPUT_DEPLETED;
     }
-    if (c->out + cnt > c->out_end) {
-        cnt = c->out_end - c->out;
+    if (dst + cnt > c->out_end) {
+        cnt = c->out_end - dst;
         c->error |= LZO_OUTPUT_FULL;
     }
-    do {
-        *c->out++ = *c->in++;
-    } while (--cnt);
+#if defined(INBUF_PADDED) && defined(OUTBUF_PADDED)
+    dst[0] = src[0];
+    dst[1] = src[1];
+    dst[2] = src[2];
+    dst[3] = src[3];
+    src += 4;
+    dst += 4;
+    cnt -= 4;
+    if (cnt > 0)
+#endif
+        memcpy(dst, src, cnt);
+    c->in = src + cnt;
+    c->out = dst + cnt;
 }
 
 /**
@@ -78,17 +96,55 @@
  * cnt > back is valid, this will copy the bytes we just copied.
  */
 static inline void copy_backptr(LZOContext *c, int back, int cnt) {
-    if (c->out - back < c->out_end - c->out_size) {
+    register uint8_t *src = &c->out[-back];
+    register uint8_t *dst = c->out;
+    if (src < c->out_start) {
         c->error |= LZO_INVALID_BACKPTR;
         return;
     }
-    if (c->out + cnt > c->out_end) {
-        cnt = c->out_end - c->out;
+    if (dst + cnt > c->out_end) {
+        cnt = c->out_end - dst;
         c->error |= LZO_OUTPUT_FULL;
     }
-    do {
-        *c->out++ = c->out[-back];
-    } while (--cnt);
+    if (back == 1) {
+        memset(dst, *src, cnt);
+        dst += cnt;
+    } else {
+#ifdef OUTBUF_PADDED
+        dst[0] = src[0];
+        dst[1] = src[1];
+        dst[2] = src[2];
+        dst[3] = src[3];
+        src += 4;
+        dst += 4;
+        cnt -= 4;
+        if (cnt > 0) {
+            dst[0] = src[0];
+            dst[1] = src[1];
+            dst[2] = src[2];
+            dst[3] = src[3];
+            dst[4] = src[4];
+            dst[5] = src[5];
+            dst[6] = src[6];
+            dst[7] = src[7];
+            src += 8;
+            dst += 8;
+            cnt -= 8;
+        }
+#endif
+        if (cnt > 0) {
+            int blocklen = back;
+            while (cnt > blocklen) {
+                memcpy(dst, src, blocklen);
+                dst += blocklen;
+                cnt -= blocklen;
+                blocklen <<= 1;
+            }
+            memcpy(dst, src, cnt);
+        }
+        dst += cnt;
+    }
+    c->out = dst;
 }
 
 /**
@@ -98,6 +154,9 @@
  * \param in input buffer
  * \param inlen size of input buffer, number of bytes left are returned here
  * \return 0 on success, otherwise error flags, see lzo.h
+ *
+ * make sure all buffers are appropriately padded, in must provide
+ * LZO_INPUT_PADDING, out must provide LZO_OUTPUT_PADDING additional bytes
  */
 int lzo1x_decode(void *out, int *outlen, void *in, int *inlen) {
     enum {COPY, BACKPTR} state = COPY;
@@ -105,9 +164,8 @@
     LZOContext c;
     c.in = in;
     c.in_end = in + *inlen;
-    c.out = out;
+    c.out = c.out_start = out;
     c.out_end = out + * outlen;
-    c.out_size = *outlen;
     c.error = 0;
     x = get_byte(&c);
     if (x > 17) {
Index: libavcodec/lzo.h
===================================================================
RCS file: /cvsroot/ffmpeg/ffmpeg/libavcodec/lzo.h,v
retrieving revision 1.1
diff -u -r1.1 lzo.h
--- libavcodec/lzo.h	12 Jan 2006 17:52:41 -0000	1.1
+++ libavcodec/lzo.h	15 Jan 2006 17:17:15 -0000
@@ -6,6 +6,9 @@
 #define LZO_INVALID_BACKPTR 4
 #define LZO_ERROR 8
 
+#define LZO_INPUT_PADDING 4
+#define LZO_OUTPUT_PADDING 12
+
 int lzo1x_decode(void *out, int *outlen, void *in, int *inlen);
 
 #endif



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