faster ff_sqrt()

Originally committed as revision 859 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/common.c

@@ -20,6 +20,13 @@
  */
 #include "avcodec.h"
 
+const UINT8 ff_sqrt_tab[128]={
+        0, 1, 1, 1, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5,
+        5, 5, 5, 5, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
+        8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9,
+        9, 9, 9, 9,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,11,11,11,11,11,11,11
+};
+
 void init_put_bits(PutBitContext *s, 
                    UINT8 *buffer, int buffer_size,
                    void *opaque,

libavcodec/common.h

@@ -901,6 +901,8 @@ static inline int clip(int a, int amin, int amax)
 }
 
 /* math */
+extern const UINT8 ff_sqrt_tab[128];
+
 int ff_gcd(int a, int b);
 
 static inline int ff_sqrt(int a)
@@ -909,6 +911,8 @@ static inline int ff_sqrt(int a)
     int s;
     int ret_sq=0;
     
+    if(a<128) return ff_sqrt_tab[a];
+    
     for(s=15; s>=0; s--){
         int b= ret_sq + (1<<(s*2)) + (ret<<s)*2;
         if(b<=a){