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libjpeg库分析----5.提取出的fdct算法

分类： LINUX

2016-07-08 19:02:15

在libgpeg-6b的jfdctint.c中是fdct的算法，现在提取出来单独研究，看能不能搞懂。



2. 代码 
出自jpeg-6b/jfdctint.c，这儿只是加了输入与输出
  1. #include <stdio.h>
  2. #include <stdlib.h>
  3. #include <math.h>
  4. #define DCTSIZE 8
  5. #define CONST_BITS 13
  6. #define PASS1_BITS 2

  8. #define RIGHT_SHIFT(x,shft) ((x) >> (shft))
  9. #define ONE ((int) 1)
  10. #define CONST_SCALE (ONE << CONST_BITS)

  12. #define FIX(x) ((int) ((x) * CONST_SCALE + 0.5))

  14. #define DESCALE(x,n) RIGHT_SHIFT((x) + (ONE << ((n)-1)), n)

  16. #define MULTIPLY16C16(var,const) ((var) * (const))

  18. /* Some C compilers fail to reduce "FIX(constant)" at compile time, thus
  19.  * causing a lot of useless floating-point operations at run time.
  20.  * To get around this we use the following pre-calculated constants.
  21.  * If you change CONST_BITS you may want to add appropriate values.
  22.  * (With a reasonable C compiler, you can just rely on the FIX() macro...)
  23.  */
  24. #define FIX_0_298631336 ((int) 2446)    /* FIX(0.298631336) */
  25. #define FIX_0_390180644 ((int) 3196)    /* FIX(0.390180644) */
  26. #define FIX_0_541196100 ((int) 4433)    /* FIX(0.541196100) */
  27. #define FIX_0_765366865 ((int) 6270)    /* FIX(0.765366865) */
  28. #define FIX_0_899976223 ((int) 7373)    /* FIX(0.899976223) */
  29. #define FIX_1_175875602 ((int) 9633)    /* FIX(1.175875602) */
  30. #define FIX_1_501321110 ((int) 12299)    /* FIX(1.501321110) */
  31. #define FIX_1_847759065 ((int) 15137)    /* FIX(1.847759065) */
  32. #define FIX_1_961570560 ((int) 16069)    /* FIX(1.961570560) */
  33. #define FIX_2_053119869 ((int) 16819)    /* FIX(2.053119869) */
  34. #define FIX_2_562915447 ((int) 20995)    /* FIX(2.562915447) */
  35. #define FIX_3_072711026 ((int) 25172)    /* FIX(3.072711026) */

  37. /* Multiply an int variable by an int constant to yield an INT32 result.
  38.  * For 8-bit samples with the recommended scaling, all the variable
  39.  * and constant values involved are no more than 16 bits wide, so a
  40.  * 16x16->32 bit multiply can be used instead of a full 32x32 multiply.
  41.  * For 12-bit samples, a full 32-bit multiplication will be needed.
  42.  */
  43. #define MULTIPLY(var,const) MULTIPLY16C16(var,const)

  45. /*
  46.  * Perform the forward DCT on one block of samples.
  47.  */

  49. void jpeg_fdct_islow (int * data)
  50. {
  51.     int tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
  52.     int tmp10, tmp11, tmp12, tmp13;
  53.     int z1, z2, z3, z4, z5;
  54.     int *dataptr;
  55.     int ctr;

  57.     /* Pass 1: process rows. */
  58.     /* Note results are scaled up by sqrt(8) compared to a true DCT; */
  59.     /* furthermore, we scale the results by 2**PASS1_BITS. */

  61.     dataptr = data;
  62.     for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
  63.         tmp0 = dataptr[0] + dataptr[7];
  64.         tmp7 = dataptr[0] - dataptr[7];
  65.         tmp1 = dataptr[1] + dataptr[6];
  66.         tmp6 = dataptr[1] - dataptr[6];
  67.         tmp2 = dataptr[2] + dataptr[5];
  68.         tmp5 = dataptr[2] - dataptr[5];
  69.         tmp3 = dataptr[3] + dataptr[4];
  70.         tmp4 = dataptr[3] - dataptr[4];

  72.         /* Even part per LL&M figure 1 --- note that published figure is faulty;
  73.          * rotator "sqrt(2)*c1" should be "sqrt(2)*c6".
  74.          */

  76.         tmp10 = tmp0 + tmp3;
  77.         tmp13 = tmp0 - tmp3;
  78.         tmp11 = tmp1 + tmp2;
  79.         tmp12 = tmp1 - tmp2;

  81.         dataptr[0] = (int) ((tmp10 + tmp11) << PASS1_BITS);
  82.         dataptr[4] = (int) ((tmp10 - tmp11) << PASS1_BITS);

  84.         z1 = MULTIPLY(tmp12 + tmp13, FIX_0_541196100);
  85.         dataptr[2] = (int) DESCALE(z1 + MULTIPLY(tmp13, FIX_0_765366865),
  86.                 CONST_BITS-PASS1_BITS);
  87.         dataptr[6] = (int) DESCALE(z1 + MULTIPLY(tmp12, - FIX_1_847759065),
  88.                 CONST_BITS-PASS1_BITS);

  90.         /* Odd part per figure 8 --- note paper omits factor of sqrt(2).
  91.          * cK represents cos(K*pi/16).
  92.          * i0..i3 in the paper are tmp4..tmp7 here.
  93.          */

  95.         z1 = tmp4 + tmp7;
  96.         z2 = tmp5 + tmp6;
  97.         z3 = tmp4 + tmp6;
  98.         z4 = tmp5 + tmp7;
  99.         z5 = MULTIPLY(z3 + z4, FIX_1_175875602); /* sqrt(2) * c3 */

  101.         tmp4 = MULTIPLY(tmp4, FIX_0_298631336); /* sqrt(2) * (-c1+c3+c5-c7) */
  102.         tmp5 = MULTIPLY(tmp5, FIX_2_053119869); /* sqrt(2) * ( c1+c3-c5+c7) */
  103.         tmp6 = MULTIPLY(tmp6, FIX_3_072711026); /* sqrt(2) * ( c1+c3+c5-c7) */
  104.         tmp7 = MULTIPLY(tmp7, FIX_1_501321110); /* sqrt(2) * ( c1+c3-c5-c7) */
  105.         z1 = MULTIPLY(z1, - FIX_0_899976223); /* sqrt(2) * (c7-c3) */
  106.         z2 = MULTIPLY(z2, - FIX_2_562915447); /* sqrt(2) * (-c1-c3) */
  107.         z3 = MULTIPLY(z3, - FIX_1_961570560); /* sqrt(2) * (-c3-c5) */
  108.         z4 = MULTIPLY(z4, - FIX_0_390180644); /* sqrt(2) * (c5-c3) */

  110.         z3 += z5;
  111.         z4 += z5;

  113.         dataptr[7] = (int) DESCALE(tmp4 + z1 + z3, CONST_BITS-PASS1_BITS);
  114.         dataptr[5] = (int) DESCALE(tmp5 + z2 + z4, CONST_BITS-PASS1_BITS);
  115.         dataptr[3] = (int) DESCALE(tmp6 + z2 + z3, CONST_BITS-PASS1_BITS);
  116.         dataptr[1] = (int) DESCALE(tmp7 + z1 + z4, CONST_BITS-PASS1_BITS);

  118.         dataptr += DCTSIZE;        /* advance pointer to next row */
  119.     }

  121.     /* Pass 2: process columns.
  122.      * We remove the PASS1_BITS scaling, but leave the results scaled up
  123.      * by an overall factor of 8.
  124.      */

  126.     dataptr = data;
  127.     for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
  128.         tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*7];
  129.         tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7];
  130.         tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6];
  131.         tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6];
  132.         tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5];
  133.         tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5];
  134.         tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4];
  135.         tmp4 = dataptr[DCTSIZE*3] - dataptr[DCTSIZE*4];

  137.         /* Even part per LL&M figure 1 --- note that published figure is faulty;
  138.          * rotator "sqrt(2)*c1" should be "sqrt(2)*c6".
  139.          */

  141.         tmp10 = tmp0 + tmp3;
  142.         tmp13 = tmp0 - tmp3;
  143.         tmp11 = tmp1 + tmp2;
  144.         tmp12 = tmp1 - tmp2;

  146.         dataptr[DCTSIZE*0] = (int) DESCALE(tmp10 + tmp11, PASS1_BITS);
  147.         dataptr[DCTSIZE*4] = (int) DESCALE(tmp10 - tmp11, PASS1_BITS);

  149.         z1 = MULTIPLY(tmp12 + tmp13, FIX_0_541196100);
  150.         dataptr[DCTSIZE*2] = (int) DESCALE(z1 + MULTIPLY(tmp13, FIX_0_765366865),
  151.                 CONST_BITS+PASS1_BITS);
  152.         dataptr[DCTSIZE*6] = (int) DESCALE(z1 + MULTIPLY(tmp12, - FIX_1_847759065),
  153.                 CONST_BITS+PASS1_BITS);

  155.         /* Odd part per figure 8 --- note paper omits factor of sqrt(2).
  156.          * cK represents cos(K*pi/16).
  157.          * i0..i3 in the paper are tmp4..tmp7 here.
  158.          */

  160.         z1 = tmp4 + tmp7;
  161.         z2 = tmp5 + tmp6;
  162.         z3 = tmp4 + tmp6;
  163.         z4 = tmp5 + tmp7;
  164.         z5 = MULTIPLY(z3 + z4, FIX_1_175875602); /* sqrt(2) * c3 */

  166.         tmp4 = MULTIPLY(tmp4, FIX_0_298631336); /* sqrt(2) * (-c1+c3+c5-c7) */
  167.         tmp5 = MULTIPLY(tmp5, FIX_2_053119869); /* sqrt(2) * ( c1+c3-c5+c7) */
  168.         tmp6 = MULTIPLY(tmp6, FIX_3_072711026); /* sqrt(2) * ( c1+c3+c5-c7) */
  169.         tmp7 = MULTIPLY(tmp7, FIX_1_501321110); /* sqrt(2) * ( c1+c3-c5-c7) */
  170.         z1 = MULTIPLY(z1, - FIX_0_899976223); /* sqrt(2) * (c7-c3) */
  171.         z2 = MULTIPLY(z2, - FIX_2_562915447); /* sqrt(2) * (-c1-c3) */
  172.         z3 = MULTIPLY(z3, - FIX_1_961570560); /* sqrt(2) * (-c3-c5) */
  173.         z4 = MULTIPLY(z4, - FIX_0_390180644); /* sqrt(2) * (c5-c3) */

  175.         z3 += z5;
  176.         z4 += z5;

  178.         dataptr[DCTSIZE*7] = (int) DESCALE(tmp4 + z1 + z3,
  179.                 CONST_BITS+PASS1_BITS);
  180.         dataptr[DCTSIZE*5] = (int) DESCALE(tmp5 + z2 + z4,
  181.                 CONST_BITS+PASS1_BITS);
  182.         dataptr[DCTSIZE*3] = (int) DESCALE(tmp6 + z2 + z3,
  183.                 CONST_BITS+PASS1_BITS);
  184.         dataptr[DCTSIZE*1] = (int) DESCALE(tmp7 + z1 + z4,
  185.                 CONST_BITS+PASS1_BITS);

  187.         dataptr++;            /* advance pointer to next column */
  188.     }
  189. }


  192. int main(void)
  193. {
  194. #define NUM 8
  195.     short i = 0;
  196.     short j = 0;
  197.     short u = 0;
  198.     short v = 0;
  199.     int *data = (int*) malloc(sizeof(int)*NUM * NUM);
  200.     double sum = 0.0;

  202.     int input[NUM][NUM] =
  203.     {
  204.         {-70 ,-85 ,-102 ,-68 ,-91 ,-111 ,-118 ,-112},
  205.         {-77 ,-91 ,-78 ,-71 ,-89 ,-89 ,-99 ,-118},
  206.         {-77 ,-88 ,-91 ,-85 ,-101 ,-99 ,-92 ,-97},
  207.         {-86 ,-82 ,-82 ,-72 ,-100 ,-125 ,-123 ,-101},
  208.         {-96 ,-100 ,-87 ,-72 ,-91 ,-101 ,-97 ,-110},
  209.         {-93 ,-98 ,-92 ,-79 ,-72 ,-78 ,-75 ,-81},
  210.         {-119 ,-110 ,-99 ,-100 ,-90 ,-88 ,-94 ,-77},
  211.         {-122 ,-109 ,-93 ,-111 ,-101 ,-95 ,-111 ,-96}
  212.     };
  213.     // print the input data
  214.     printf("input:\n");
  215.     for(u=0; u<NUM; u++)
  216.     {
  217.         for(v = 0; v<NUM; v++)
  218.         {
  219.             printf("%d ", input[u][v]);
  220.         }
  221.         printf("\n");
  222.     }
  223.     printf("\n");
  224.     //2D --> 1D
  225.     for(i=0; i<NUM; i++)
  226.     {
  227.         for(j=0; j<NUM; j++)
  228.         {
  229.             data[i * NUM + j] = input[i][j];
  230.         }
  231.     }
  232.     jpeg_fdct_islow(data);
  233.     // print the result of FDCT
  234.     printf("result:\n");
  235.     for(u = 0; u < NUM; u++)
  236.     {
  237.         for(v = 0; v < NUM; v++)
  238.         {
  239.             printf("%d ", data[u*NUM + v]);
  240.         }
  241.         printf("\n");
  242.     }
  243.     free(data);
  244.     return 0;
  245. }
3.运行输出结果如下
  1. input:
  2. -70 -85 -102 -68 -91 -111 -118 -112
  3. -77 -91 -78 -71 -89 -89 -99 -118
  4. -77 -88 -91 -85 -101 -99 -92 -97
  5. -86 -82 -82 -72 -100 -125 -123 -101
  6. -96 -100 -87 -72 -91 -101 -97 -110
  7. -93 -98 -92 -79 -72 -78 -75 -81
  8. -119 -110 -99 -100 -90 -88 -94 -77
  9. -122 -109 -93 -111 -101 -95 -111 -96

  11. result:
  12. -6007 197 -215 -98 157 85 6 -56
  13. 135 500 5 64 135 159 -96 -89
  14. -141 -85 4 88 -32 -89 70 -12
  15. 177 -75 -95 103 97 45 -76 -13
  16. -233 240 -43 -119 87 -38 -24 -41
  17. -64 0 122 -99 122 -101 -38 -41
  18. 81 -43 100 69 19 -3 -40 -1
  19. -78 -83 36 39 -32 41 -10 -9









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