libmpeg3/video/idct.c

   1 #include "idct.h"
   2 #include <stdlib.h>
   3
   4 /**********************************************************/
   5 /* inverse two dimensional DCT, Chen-Wang algorithm       */
   6 /* (cf. IEEE ASSP-32, pp. 803-816, Aug. 1984)             */
   7 /* 32-bit integer arithmetic (8 bit coefficients)         */
   8 /* 11 mults, 29 adds per DCT                              */
   9 /*                                      sE, 18.8.91       */
  10 /**********************************************************/
  11 /* coefficients extended to 12 bit for IEEE1180-1990      */
  12 /* compliance                           sE,  2.1.94       */
  13 /**********************************************************/
  14
  15 /* this code assumes >> to be a two's-complement arithmetic */
  16 /* right shift: (-2)>>1 == -1 , (-3)>>1 == -2               */
  17
  18 #define W1 2841 /* 2048*sqrt(2)*cos(1*pi/16) */
  19 #define W2 2676 /* 2048*sqrt(2)*cos(2*pi/16) */
  20 #define W3 2408 /* 2048*sqrt(2)*cos(3*pi/16) */
  21 #define W5 1609 /* 2048*sqrt(2)*cos(5*pi/16) */
  22 #define W6 1108 /* 2048*sqrt(2)*cos(6*pi/16) */
  23 #define W7 565  /* 2048*sqrt(2)*cos(7*pi/16) */
  24
  25 /* row (horizontal) IDCT
  26  *
  27  *           7                       pi         1
  28  * dst[k] = sum c[l] * src[l] * cos( -- * ( k + - ) * l )
  29  *          l=0                      8          2
  30  *
  31  * where: c[0]    = 128
  32  *        c[1..7] = 128*sqrt(2)
  33  */
  34
  35 int mpeg3video_idctrow(short *blk)
  36 {
  37         int x0, x1, x2, x3, x4, x5, x6, x7, x8;
  38
  39         /* shortcut */
  40         if (!((x1 = blk[4]<<11) | (x2 = blk[6]) | (x3 = blk[2]) |
  41           (x4 = blk[1]) | (x5 = blk[7]) | (x6 = blk[5]) | (x7 = blk[3])))
  42         {
  43       blk[0]=blk[1]=blk[2]=blk[3]=blk[4]=blk[5]=blk[6]=blk[7]=blk[0]<<3;
  44       return 0;
  45         }
  46
  47         x0 = (blk[0]<<11) + 128; /* for proper rounding in the fourth stage */
  48
  49         /* first stage */
  50         x8 = W7*(x4+x5);
  51         x4 = x8 + (W1-W7)*x4;
  52         x5 = x8 - (W1+W7)*x5;
  53         x8 = W3*(x6+x7);
  54         x6 = x8 - (W3-W5)*x6;
  55         x7 = x8 - (W3+W5)*x7;
  56
  57         /* second stage */
  58         x8 = x0 + x1;
  59         x0 -= x1;
  60         x1 = W6*(x3+x2);
  61         x2 = x1 - (W2+W6)*x2;
  62         x3 = x1 + (W2-W6)*x3;
  63         x1 = x4 + x6;
  64         x4 -= x6;
  65         x6 = x5 + x7;
  66         x5 -= x7;
  67
  68         /* third stage */
  69         x7 = x8 + x3;
  70         x8 -= x3;
  71         x3 = x0 + x2;
  72         x0 -= x2;
  73         x2 = (181*(x4+x5)+128)>>8;
  74         x4 = (181*(x4-x5)+128)>>8;
  75
  76         /* fourth stage */
  77         blk[0] = (x7+x1)>>8;
  78         blk[1] = (x3+x2)>>8;
  79         blk[2] = (x0+x4)>>8;
  80         blk[3] = (x8+x6)>>8;
  81         blk[4] = (x8-x6)>>8;
  82         blk[5] = (x0-x4)>>8;
  83         blk[6] = (x3-x2)>>8;
  84         blk[7] = (x7-x1)>>8;
  85         return 0;
  86 }
  87
  88 /* column (vertical) IDCT
  89  *
  90  *             7                         pi         1
  91  * dst[8*k] = sum c[l] * src[8*l] * cos( -- * ( k + - ) * l )
  92  *            l=0                        8          2
  93  *
  94  * where: c[0]    = 1/1024
  95  *        c[1..7] = (1/1024)*sqrt(2)
  96  */
  97
  98 int mpeg3video_idctcol(short *blk)
  99 {
 100   int x0, x1, x2, x3, x4, x5, x6, x7, x8;
 101
 102   /* shortcut */
 103   if (!((x1 = (blk[8 * 4]<<8)) | (x2 = blk[8 * 6]) | (x3 = blk[8 * 2]) |
 104         (x4 = blk[8*1]) | (x5 = blk[8 * 7]) | (x6 = blk[8 * 5]) | (x7 = blk[8 * 3]))){
 105     blk[8*0]=blk[8*1]=blk[8 * 2]=blk[8 * 3]=blk[8 * 4]=blk[8 * 5]=blk[8 * 6]=blk[8 * 7]=
 106       (blk[8*0]+32)>>6;
 107     return 0;
 108   }
 109
 110         x0 = (blk[8*0]<<8) + 8192;
 111
 112         /* first stage */
 113         x8 = W7*(x4+x5) + 4;
 114         x4 = (x8+(W1-W7)*x4)>>3;
 115         x5 = (x8-(W1+W7)*x5)>>3;
 116         x8 = W3*(x6+x7) + 4;
 117         x6 = (x8-(W3-W5)*x6)>>3;
 118         x7 = (x8-(W3+W5)*x7)>>3;
 119
 120         /* second stage */
 121         x8 = x0 + x1;
 122         x0 -= x1;
 123         x1 = W6*(x3+x2) + 4;
 124         x2 = (x1-(W2+W6)*x2)>>3;
 125         x3 = (x1+(W2-W6)*x3)>>3;
 126         x1 = x4 + x6;
 127         x4 -= x6;
 128         x6 = x5 + x7;
 129         x5 -= x7;
 130
 131         /* third stage */
 132         x7 = x8 + x3;
 133         x8 -= x3;
 134         x3 = x0 + x2;
 135         x0 -= x2;
 136         x2 = (181 * (x4 + x5) + 128) >> 8;
 137         x4 = (181 * (x4 - x5) + 128) >> 8;
 138
 139         /* fourth stage */
 140         blk[8 * 0] = (x7 + x1) >> 14;
 141         blk[8 * 1] = (x3 + x2) >> 14;
 142         blk[8 * 2] = (x0 + x4) >> 14;
 143         blk[8 * 3] = (x8 + x6) >> 14;
 144         blk[8 * 4] = (x8 - x6) >> 14;
 145         blk[8 * 5] = (x0 - x4) >> 14;
 146         blk[8 * 6] = (x3 - x2) >> 14;
 147         blk[8 * 7] = (x7 - x1) >> 14;
 148         return 0;
 149 }
 150
 151
 152 /* two dimensional inverse discrete cosine transform */
 153 void mpeg3video_idct_conversion(short* block)
 154 {
 155         int i;
 156         for(i = 0; i < 8; i++) mpeg3video_idctrow(block + 8 * i);
 157         for(i = 0; i < 8; i++) mpeg3video_idctcol(block + i);
 158 }