LE bitstream reader based upon a patch by (Balatoni Denes <dbalatoni programozo hu)

Originally committed as revision 4215 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/bitstream.c

@@ -132,14 +132,14 @@ static int build_table(VLC *vlc, int table_nb_bits,
                        int nb_codes,
                        const void *bits, int bits_wrap, int bits_size,
                        const void *codes, int codes_wrap, int codes_size,
-                       uint32_t code_prefix, int n_prefix, int use_static)
+                       uint32_t code_prefix, int n_prefix, int flags)
 {
-    int i, j, k, n, table_size, table_index, nb, n1, index;
+    int i, j, k, n, table_size, table_index, nb, n1, index, code_prefix2;
     uint32_t code;
     VLC_TYPE (*table)[2];
 
     table_size = 1 << table_nb_bits;
-    table_index = alloc_table(vlc, table_size, use_static);
+    table_index = alloc_table(vlc, table_size, flags & INIT_VLC_USE_STATIC);
 #ifdef DEBUG_VLC
     printf("new table index=%d size=%d code_prefix=%x n=%d\n",
            table_index, table_size, code_prefix, n_prefix);
@@ -165,12 +165,18 @@ static int build_table(VLC *vlc, int table_nb_bits,
 #endif
         /* if code matches the prefix, it is in the table */
         n -= n_prefix;
-        if (n > 0 && (code >> n) == code_prefix) {
+        if(flags & INIT_VLC_LE)
+            code_prefix2= code & (n_prefix>=32 ? 0xffffffff : (1 << n_prefix)-1);
+        else
+            code_prefix2= code >> n;
+        if (n > 0 && code_prefix2 == code_prefix) {
             if (n <= table_nb_bits) {
                 /* no need to add another table */
                 j = (code << (table_nb_bits - n)) & (table_size - 1);
                 nb = 1 << (table_nb_bits - n);
                 for(k=0;k<nb;k++) {
+                    if(flags & INIT_VLC_LE)
+                        j = (code >> n_prefix) + (k<<n);
 #ifdef DEBUG_VLC
                     av_log(NULL, AV_LOG_DEBUG, "%4x: code=%d n=%d\n",
                            j, i, n);
@@ -185,7 +191,7 @@ static int build_table(VLC *vlc, int table_nb_bits,
                 }
             } else {
                 n -= table_nb_bits;
-                j = (code >> n) & ((1 << table_nb_bits) - 1);
+                j = (code >> ((flags & INIT_VLC_LE) ? n_prefix : n)) & ((1 << table_nb_bits) - 1);
 #ifdef DEBUG_VLC
                 printf("%4x: n=%d (subtable)\n",
                        j, n);
@@ -211,8 +217,8 @@ static int build_table(VLC *vlc, int table_nb_bits,
             index = build_table(vlc, n, nb_codes,
                                 bits, bits_wrap, bits_size,
                                 codes, codes_wrap, codes_size,
-                                (code_prefix << table_nb_bits) | i,
-                                n_prefix + table_nb_bits, use_static);
+                                (flags & INIT_VLC_LE) ? (code_prefix | (i << n_prefix)) : ((code_prefix << table_nb_bits) | i),
+                                n_prefix + table_nb_bits, flags);
             if (index < 0)
                 return -1;
             /* note: realloc has been done, so reload tables */

libavcodec/bitstream.h

@@ -368,6 +368,16 @@ static inline int unaligned32_be(const void *v)
 #endif
 }
 
+static inline int unaligned32_le(const void *v)
+{
+#ifdef CONFIG_ALIGN
+       const uint8_t *p=v;
+       return (((p[3]<<8) | p[2])<<16) | (p[1]<<8) | (p[0]);
+#else
+       return le2me_32( unaligned32(v)); //original
+#endif
+}
+
 #ifdef ALT_BITSTREAM_READER
 #   define MIN_CACHE_BITS 25
 
@@ -378,11 +388,19 @@ static inline int unaligned32_be(const void *v)
 #   define CLOSE_READER(name, gb)\
         (gb)->index= name##_index;\
 
+# ifdef ALT_BITSTREAM_READER_LE
+#   define UPDATE_CACHE(name, gb)\
+        name##_cache= unaligned32_le( ((const uint8_t *)(gb)->buffer)+(name##_index>>3) ) >> (name##_index&0x07);\
+
+#   define SKIP_CACHE(name, gb, num)\
+        name##_cache >>= (num);
+# else
 #   define UPDATE_CACHE(name, gb)\
         name##_cache= unaligned32_be( ((const uint8_t *)(gb)->buffer)+(name##_index>>3) ) << (name##_index&0x07);\
 
 #   define SKIP_CACHE(name, gb, num)\
-        name##_cache <<= (num);\
+        name##_cache <<= (num);
+# endif
 
 // FIXME name?
 #   define SKIP_COUNTER(name, gb, num)\
@@ -397,8 +415,13 @@ static inline int unaligned32_be(const void *v)
 #   define LAST_SKIP_BITS(name, gb, num) SKIP_COUNTER(name, gb, num)
 #   define LAST_SKIP_CACHE(name, gb, num) ;
 
+# ifdef ALT_BITSTREAM_READER_LE
+#   define SHOW_UBITS(name, gb, num)\
+        ((name##_cache) & (NEG_USR32(0xffffffff,num)))
+# else
 #   define SHOW_UBITS(name, gb, num)\
         NEG_USR32(name##_cache, num)
+# endif
 
 #   define SHOW_SBITS(name, gb, num)\
         NEG_SSR32(name##_cache, num)
@@ -616,8 +639,13 @@ static inline unsigned int get_bits1(GetBitContext *s){
 #ifdef ALT_BITSTREAM_READER
     int index= s->index;
     uint8_t result= s->buffer[ index>>3 ];
+#ifdef ALT_BITSTREAM_READER_LE
+    result>>= (index&0x07);
+    result&= 1;
+#else
     result<<= (index&0x07);
     result>>= 8 - 1;
+#endif
     index++;
     s->index= index;
 
@@ -687,7 +715,9 @@ void align_get_bits(GetBitContext *s);
 int init_vlc(VLC *vlc, int nb_bits, int nb_codes,
              const void *bits, int bits_wrap, int bits_size,
              const void *codes, int codes_wrap, int codes_size,
-             int use_static);
+             int flags);
+#define INIT_VLC_USE_STATIC 1
+#define INIT_VLC_LE         2
 void free_vlc(VLC *vlc);
 
 /**