[SCM] libav/experimental: get_vlc() optimization

[siretart at users.alioth.debian.org]

The following commit has been merged in the experimental branch:
commit cceabc8656118f2a5478a17264df434a63838691
Author: Michael Niedermayer <michaelni at gmx.at>
Date:   Wed Jul 10 17:32:59 2002 +0000

    get_vlc() optimization
    
    Originally committed as revision 735 to svn://svn.ffmpeg.org/ffmpeg/trunk

diff --git a/libavcodec/common.c b/libavcodec/common.c
index 63d17b6..abfa190 100644
--- a/libavcodec/common.c
+++ b/libavcodec/common.c
@@ -286,7 +286,7 @@ static int build_table(VLC *vlc, int table_nb_bits,
                 return -1;
             /* note: realloc has been done, so reload tables */
             table = &vlc->table[table_index];
-            table[i][0] = index; //code
+            table[i][0] = index - table_index; //code
         }
     }
     return table_index;
diff --git a/libavcodec/common.h b/libavcodec/common.h
index 61eee5f..35c04a8 100644
--- a/libavcodec/common.h
+++ b/libavcodec/common.h
@@ -732,64 +732,54 @@ int init_vlc(VLC *vlc, int nb_bits, int nb_codes,
              const void *codes, int codes_wrap, int codes_size);
 void free_vlc(VLC *vlc);
 
+//note table will be trashed (pointer increased)
+#define GET_VLC(code, name, gb, table, bits, max_depth)\
+{\
+    int n, index, nb_bits;\
+\
+    index= SHOW_UBITS(name, gb, bits);\
+    code = table[index][0];\
+    n    = table[index][1];\
+\
+    if(max_depth > 1 && n < 0){\
+        LAST_SKIP_BITS(name, gb, bits)\
+        UPDATE_CACHE(name, gb)\
+\
+        nb_bits = -n;\
+        table += code;\
+\
+        index= SHOW_UBITS(name, gb, nb_bits);\
+        code = table[index][0];\
+        n    = table[index][1];\
+        if(max_depth > 2 && n < 0){\
+            LAST_SKIP_BITS(name, gb, nb_bits)\
+            UPDATE_CACHE(name, gb)\
+\
+            nb_bits = -n;\
+            table += code;\
+\
+            index= SHOW_UBITS(name, gb, nb_bits);\
+            code = table[index][0];\
+            n    = table[index][1];\
+        }\
+    }\
+    SKIP_BITS(name, gb, n)\
+}
+
 static inline int get_vlc(GetBitContext *s, VLC *vlc)
 {
-    int code, n, nb_bits, index;
-    VLC_TYPE (*table)[2];
+    int code;
+    VLC_TYPE (*table)[2]= vlc->table;
+    
     OPEN_READER(re, s)
-
     UPDATE_CACHE(re, s)
 
-    nb_bits = vlc->bits;
-    table = vlc->table;
-
-#ifdef FAST_GET_FIRST_VLC
-    index= SHOW_UBITS(re, s, nb_bits);
-    code = table[index][0];
-    n = table[index][1];
-    if (n > 0) {
-        /* most common case (90%)*/
-        LAST_SKIP_BITS(re, s, n)
-        CLOSE_READER(re, s)
-        return code;
-    } else if (n == 0) {
-        return -1;
-    } else {
-        LAST_SKIP_BITS(re, s, nb_bits)
-        UPDATE_CACHE(re, s) //this isnt needed but its faster if its here
+    GET_VLC(code, re, s, table, vlc->bits, 3)    
 
-        nb_bits = -n;
-        table = vlc->table + code;
-    }
-#endif
-    for(;;) {
-        index= SHOW_UBITS(re, s, nb_bits);
-        code = table[index][0];
-        n = table[index][1];
-        if (n > 0) {
-            /* most common case */
-            SKIP_BITS(re, s, n)
-#ifdef STATS
-            st_bit_counts[st_current_index] += n;
-#endif
-            break;
-        } else if (n == 0) {
-            return -1;
-        } else {
-            LAST_SKIP_BITS(re, s, nb_bits)
-            UPDATE_CACHE(re, s)
-#ifdef STATS
-            st_bit_counts[st_current_index] += nb_bits;
-#endif
-            nb_bits = -n;
-            table = vlc->table + code;
-        }
-    }
     CLOSE_READER(re, s)
     return code;
 }
 
-
 /* define it to include statistics code (useful only for optimizing
    codec efficiency */
 //#define STATS

-- 
Libav/FFmpeg packaging