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  1. So I was scrolling through twinvq_tables.h and almost all of it is just a shitload of VQ tables and yes the spec really DOES explicitly define each and every single one of them. However, if you get to the very end, you'll notice a surprise:
  2.  
  3. #include <stdint.h>
  4. static inline unsigned int av_log2(unsigned int x) {                            
  5.    unsigned int ret;
  6.    x |= 1;                                                          
  7.    __asm__ volatile("bsr %1, %0 \n\t" :"=a"(ret) :"r"(x));                                              
  8.    return ret;                                                                
  9. }
  10.  
  11. static const uint8_t tab7[][35] = {
  12.    {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,1,0,0,0},
  13.    {0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0},
  14.    {0,0,0,1,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0},
  15.    {0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0},
  16.    {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,1,0,0,0},
  17.    {0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0},
  18.    {0,0,0,1,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0},
  19.    {0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0},
  20.    {0,0,1,0,1,0,0,1,0,1,0,0,1,0,1,0,0,1,0,1,0,0,1,0,1,0,0,1,0,1,0,0,1,0,1},
  21.    {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0},
  22.    {0,0,0,0,0,0,1,0,0,1,0,0,0,0,0,0,0,0,0,0,0,1,0,0,1,0,0,0,0,0,0,0,0,0,0}
  23. };
  24.  
  25. static const uint8_t tab8[][5] = {
  26.    {0, 0, 0, 1, 1},
  27.    {0, 1, 0, 0, 1},
  28.    {1, 1, 0, 0, 0},
  29.    {1, 0, 0, 1, 0},
  30.    {0, 0, 0, 1, 1},
  31.    {0, 1, 0, 0, 1},
  32.    {1, 1, 0, 0, 0},
  33.    {1, 0, 0, 1, 0},
  34.    {0, 0, 0, 1, 1},
  35.    {0, 1, 0, 0, 1},
  36.    {1, 1, 0, 0, 0},
  37.    {0, 0, 0, 0, 0},
  38.    {0, 1, 0, 1, 0}
  39. };
  40.  
  41. static const uint8_t tab9[][45] = {
  42.    {
  43.     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  44.     0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0
  45.    },{
  46.     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  47.     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0
  48.    },{
  49.     0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  50.     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
  51.    },{
  52.     0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  53.     0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
  54.    },{
  55.     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  56.     0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0
  57.    },{
  58.     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  59.     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0
  60.    },{
  61.     0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  62.     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
  63.    },{
  64.     0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  65.     0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
  66.    },{
  67.     0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1,
  68.     1, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0
  69.    },{
  70.     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0,
  71.     0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
  72.    }
  73. };
  74.  
  75. static const uint8_t tab10[][25] =
  76. {
  77.    {1, 1, 0, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 0, 1, 0, 0, 1, 0, 1, 1, 0, 1, 1, 0},
  78.    {1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 0, 1, 0, 0, 1, 0, 0, 1, 0, 0, 1, 0, 0},
  79.    {1, 1, 1, 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 1, 1, 1, 0, 0, 0},
  80.    {1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0},
  81.    {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1},
  82.    {0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1},
  83.    {0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1},
  84.    {1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0},
  85.    {0, 1, 0, 1, 1, 0, 1, 0, 1, 0, 1, 0, 0, 1, 0, 1, 0, 1, 0, 1, 0, 0, 1, 0, 1}
  86. };
  87.  
  88. static const uint8_t tab11[][55] = {
  89.    {  
  90.        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  91.        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0,
  92.        0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0
  93.    },{
  94.        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0,
  95.        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  96.        0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0,
  97.    },{
  98.        0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0,
  99.        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  100.        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  101.    },{
  102.        0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  103.        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0,
  104.        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  105.    }, {
  106.        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  107.        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0,
  108.        0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0,
  109.    },{
  110.        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0,
  111.        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  112.        0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0,
  113.    },{
  114.        0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0,
  115.        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  116.        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  117.    },{
  118.        0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  119.        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0,
  120.        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  121.    },{
  122.        0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0,
  123.        0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  124.        1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0,
  125.    }
  126. };
  127.  
  128. static const uint8_t tab12[][15] = {
  129.    {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0},
  130.    {0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0},
  131.    {0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
  132.    {0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0},
  133.    {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0},
  134.    {0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0},
  135.    {0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
  136.    {0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0},
  137.    {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0},
  138.    {0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0},
  139.    {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1},
  140. };
  141.  
  142. static const struct {
  143.    int size;
  144.    const uint8_t *tab;
  145. } tabs[] = {
  146.    {0 , NULL},
  147.    {5 , &tab8 [0][0]},{5 , &tab8 [0][0]}, {15, &tab12[0][0]},
  148.    {5 , &tab8 [0][0]},{25, &tab10[0][0]}, {15, &tab12[0][0]},
  149.    {35, &tab7 [0][0]},{5 , &tab8 [0][0]}, {45, &tab9 [0][0]},
  150.    {25, &tab10[0][0]},{55, &tab11[0][0]}, {15, &tab12[0][0]}
  151. };
  152.  
  153. /* In twinqv.c */
  154. /**
  155. * Evaluate a*b/400 rounded to the nearest integer. When, for example,
  156. * a*b == 200 and the nearest integer is ill-defined, use a table to emulate
  157. * the following broken float-based implementation used by the binary decoder:
  158. *
  159. * \code
  160. * static int very_broken_op(int a, int b)
  161. * {
  162. *    static float test; // Ugh, force gcc to do the division first...
  163. *
  164. *    test = a/400.;
  165. *    return b * test +  0.5;
  166. * }
  167. * \endcode
  168. *
  169. * @note if this function is replaced by just ROUNDED_DIV(a*b,400.), the stddev
  170. * between the original file (before encoding with Yamaha encoder) and the
  171. * decoded output increases, which leads one to believe that the encoder expects
  172. * exactly this broken calculation.
  173. */
  174. int very_broken_op(int a, int b)
  175. {
  176.    int x = a*b + 200;
  177.    int size;
  178.    const uint8_t *rtab;
  179.  
  180.    if (x%400 || b%5)
  181.        return x/400;
  182.  
  183.    x /= 400;
  184.  
  185.    size = tabs[b/5].size;
  186.    rtab = tabs[b/5].tab;
  187.    return x - rtab[size*av_log2(2*(x - 1)/size)+(x - 1)%size];
  188. }
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