Additional optimization to new bisection search codebook decode

svn path=/trunk/vorbis/; revision=2970

diff --git a/lib/codebook.c b/lib/codebook.c
index b89f077..469a530 100644 (file)
--- a/lib/codebook.c
+++ b/lib/codebook.c
@@ -11,7 +11,7 @@
  ********************************************************************
 
  function: basic codebook pack/unpack/code/decode operations
- last mod: $Id: codebook.c,v 1.36 2002/01/19 04:52:39 xiphmont Exp $
+ last mod: $Id: codebook.c,v 1.37 2002/01/21 20:51:28 xiphmont Exp $
 
  ********************************************************************/
 
@@ -315,39 +315,40 @@ static ogg_uint32_t bitreverse(ogg_uint32_t x){
   return((x>> 1)&0x55555555) | ((x<< 1)&0xaaaaaaaa);
 }
 
+
 static long decode_packed_entry_number(codebook *book, oggpack_buffer *b){
-  int read;
+  int  read=book->dec_maxlength;
+  long lo,hi;
   long lok = oggpack_look(b, book->dec_firsttablen);
 
   if (lok >= 0) {
     long entry = book->dec_firsttable[lok];
-    if(entry>=0){
-      oggpack_adv(b, book->dec_codelengths[entry]);
-      return(entry);
+    if(entry&0x80000000UL){
+      lo=(entry>>15)&0x7fff;
+      hi=book->used_entries-(entry&0x7fff);
+    }else{
+      oggpack_adv(b, book->dec_codelengths[entry-1]);
+      return(entry-1);
     }
+  }else{
+    lo=0;
+    hi=book->used_entries;
   }
 
-  read=book->dec_maxlength;
   lok = oggpack_look(b, read);
-
   while(lok<0 && read>1)
     lok = oggpack_look(b, --read);
-
   if(lok<0)return -1;
 
   /* bisect search for the codeword in the ordered list */
   {
     ogg_uint32_t testword=bitreverse((ogg_uint32_t)lok);
-
-    long lo=0;
-    long hi=book->used_entries;
     long p=(lo+hi)>>1;
 
     while(hi-lo>1){
-      if(book->codelist[p]<=testword)
-       lo=p;
-      else
-       hi=p;
+      long test=(book->codelist[p]<=testword)-1;
+      lo+=(p-lo)&(~test);
+      hi-=(hi-p)&test;
       p=(lo+hi)>>1;
     }
 

diff --git a/lib/codebook.h b/lib/codebook.h
index 538169f..5800546 100644 (file)
--- a/lib/codebook.h
+++ b/lib/codebook.h
@@ -11,7 +11,7 @@
  ********************************************************************
 
  function: basic shared codebook operations
- last mod: $Id: codebook.h,v 1.11 2002/01/19 04:52:40 xiphmont Exp $
+ last mod: $Id: codebook.h,v 1.12 2002/01/21 20:51:28 xiphmont Exp $
 
  ********************************************************************/
 
@@ -110,7 +110,7 @@ typedef struct codebook{
 
   int          *dec_index;  /* only used if sparseness collapsed */
   char         *dec_codelengths;
-  int          *dec_firsttable;
+  ogg_uint32_t *dec_firsttable;
   int           dec_firsttablen;
   int           dec_maxlength;
 

diff --git a/lib/sharedbook.c b/lib/sharedbook.c
index e6746c3..40235fc 100644 (file)
--- a/lib/sharedbook.c
+++ b/lib/sharedbook.c
@@ -11,7 +11,7 @@
  ********************************************************************
 
  function: basic shared codebook operations
- last mod: $Id: sharedbook.c,v 1.24 2002/01/19 05:01:44 xiphmont Exp $
+ last mod: $Id: sharedbook.c,v 1.25 2002/01/21 20:51:28 xiphmont Exp $
 
  ********************************************************************/
 
@@ -312,7 +312,6 @@ static int sort32a(const void *a,const void *b){
   return ( (**(ogg_uint32_t **)a>**(ogg_uint32_t **)b)<<1)-1;
 }
 
-
 /* decode codebook arrangement is more heavily optimized than encode */
 int vorbis_book_init_decode(codebook *c,const static_codebook *s){
   int i,j,n=0,tabn;
@@ -382,8 +381,7 @@ int vorbis_book_init_decode(codebook *c,const static_codebook *s){
   if(c->dec_firsttablen>8)c->dec_firsttablen=8;
 
   tabn=1<<c->dec_firsttablen;
-  c->dec_firsttable=_ogg_malloc(tabn*sizeof(*c->dec_firsttable));
-  for(i=0;i<tabn;i++)c->dec_firsttable[i]=-1;
+  c->dec_firsttable=_ogg_calloc(tabn,sizeof(*c->dec_firsttable));
   c->dec_maxlength=0;
 
   for(i=0;i<n;i++){
@@ -392,9 +390,37 @@ int vorbis_book_init_decode(codebook *c,const static_codebook *s){
     if(c->dec_codelengths[i]<=c->dec_firsttablen){
       ogg_uint32_t orig=bitreverse(c->codelist[i]);
       for(j=0;j<(1<<(c->dec_firsttablen-c->dec_codelengths[i]));j++)
-       c->dec_firsttable[orig|(j<<c->dec_codelengths[i])]=i;
+       c->dec_firsttable[orig|(j<<c->dec_codelengths[i])]=i+1;
+    }
+  }
+
+  /* now fill in 'unused' entries in the firsttable with hi/lo search
+     hints for the non-direct-hits */
+  {
+    ogg_uint32_t mask=0xfffffffeUL<<(31-c->dec_firsttablen);
+
+    for(i=0;i<tabn;i++){
+      if(c->dec_firsttable[i]==0){
+       ogg_uint32_t testword=bitreverse(i);
+       long lo=0,hi=0;
+       while((lo+1)<n && c->codelist[lo+1]<=testword)lo++;
+       while(    hi<n && testword>=(c->codelist[hi]&mask))hi++;
+
+       /* we only actually have 15 bits per hint to play with here.
+           In order to overflow gracefully (nothing breaks, efficiency
+           just drops), encode as the difference from the extremes. */
+       {
+         unsigned long loval=lo;
+         unsigned long hival=n-hi;
+
+         if(loval>0x7fff)loval=0x7fff;
+         if(hival>0x7fff)hival=0x7fff;
+         c->dec_firsttable[i]=0x80000000UL | (loval<<15) | hival;
+       }
+      }
     }
   }
+  
 
   return(0);
  err_out: