dct.c

这是一个JPEG编码源代码

#include "jinclude.h"

void
fdct1_8x8(DCTVAL *in) {
  float c1 = 0.9808;
  float c2 = 0.9239;
  float c3 = 0.8315;
  float c4 = 0.7071;
  float c5 = 0.5556;
  float c6 = 0.3827;
  float c7 = 0.1951;

  int col, row;
  DCTVAL *data = in, *tdata[DCTSIZE];

  for (row=0; row<DCTSIZE; row++) {
    /* sum of data */
    int s07 = data[0] + data[7];
    int s16 = data[1] + data[6];
    int s25 = data[2] + data[5];
    int s34 = data[3] + data[4];
    int s0734 = s07 + s34;
    int s1625 = s16 + s25;

    /* dif of data */
    int d07 = data[0] - data[7];
    int d16 = data[1] - data[6];
    int d25 = data[2] - data[5];
    int d34 = data[3] - data[4];
    int d0734 = d07 - d34;
    int d1625 = d16 - d25;

    data[0] = (c4 * (s0734 + s1625));
    data[1] = (c1*d07 + c3*d16 + c5*d25 + c7*d34);
    data[2] = (c2*d0734 + c6*d1625);
    data[3] = (c3*d07 - c7*d16 - c1*d25 - c5*d34);
    data[4] = (c4 * (s0734 - s1625));
    data[5] = (c5*d07 - c1*d16 + c7*d25 + c3*d34);
    data[6] = (c6*d0734 - c2*d1625);
    data[7] = (c7*d07 - c5*d16 + c3*d25 - c1*d34);

    data[0] >>= 1;
    data[1] >>= 1;
    data[2] >>= 1;
    data[3] >>= 1;
    data[4] >>= 1;
    data[5] >>= 1;
    data[6] >>= 1;
    data[7] >>= 1;

    data += DCTSIZE;
  }

  data = in;
  for (col=0; col<DCTSIZE; col++) {
    int ii,s07,s16,s25,s34,s0734,s1625;
	int d07,d16,d25,d34,d0734,d1625;
    DCTVAL *tmp = data;
    for (ii=0; ii<DCTSIZE; ii++) {
      tdata[ii] = tmp;
      tmp += DCTSIZE;
    }

    /* sum of data */
     s07 = *tdata[0] + *tdata[7];
     s16 = *tdata[1] + *tdata[6];
     s25 = *tdata[2] + *tdata[5];
     s34 = *tdata[3] + *tdata[4];
     s0734 = s07 + s34;
     s1625 = s16 + s25;

    /* dif of data */
     d07 = *tdata[0] - *tdata[7];
     d16 = *tdata[1] - *tdata[6];
     d25 = *tdata[2] - *tdata[5];
     d34 = *tdata[3] - *tdata[4];
     d0734 = d07 - d34;
     d1625 = d16 - d25;

    *tdata[0] = (c4 * (s0734 + s1625));
    *tdata[1] = (c1*d07 + c3*d16 + c5*d25 + c7*d34);
    *tdata[2] = (c2*d0734 + c6*d1625);
    *tdata[3] = (c3*d07 - c7*d16 - c1*d25 - c5*d34);
    *tdata[4] = (c4 * (s0734 - s1625));
    *tdata[5] = (c5*d07 - c1*d16 + c7*d25 + c3*d34);
    *tdata[6] = (c6*d0734 - c2*d1625);
    *tdata[7] = (c7*d07 - c5*d16 + c3*d25 - c1*d34);

    *tdata[0] >>= 1;
    *tdata[1] >>= 1;
    *tdata[2] >>= 1;
    *tdata[3] >>= 1;
    *tdata[4] >>= 1;
    *tdata[5] >>= 1;
    *tdata[6] >>= 1;
    *tdata[7] >>= 1;

    data++;
  }
}      

void fdct2_8x8(short *dct_data)
{
  const unsigned short c1 = 0x2C62, c3 = 0x25A0;
  const unsigned short c5 = 0x1924, c7 = 0x08D4;
  const unsigned short c0 = 0xB505, c2 = 0x29CF;
  const unsigned short c6 = 0x1151;

  short f0, f1, f2, f3,
        f4, f5, f6, f7;
  int   g0, g1, h0, h1,
        p0, p1;
  short r0, r1;
  int   P0, P1, R0, R1;
  short g2, g3, h2, h3;
  short q0a,s0a,q0, q1,
        s0, s1;
  short Q0, Q1, S0, S1;
  int   F0, F1, F2, F3,
        F4, F5, F6, F7;
  int   F0r,F1r,F2r,F3r,
        F4r,F5r,F6r,F7r;

  unsigned i, j;
  short    *data;

  data= dct_data;
  
  
      for (j = 0; j < 8; j++)
      {
          f0 = data[ 0];
          f1 = data[ 8];
          f2 = data[16];
          f3 = data[24];
          f4 = data[32];
          f5 = data[40];
          f6 = data[48];
          f7 = data[56];

          g0 = f0 + f7;               h2 = f0 - f7;
          g1 = f1 + f6;               h3 = f1 - f6;
          h1 = f2 + f5;               g3 = f2 - f5;
          h0 = f3 + f4;               g2 = f3 - f4;

          p0 = g0 + h0;               r0 = g0 - h0;
          p1 = g1 + h1;               r1 = g1 - h1;
          q1 = g2;                    s1 = h2;

          s0a= h3 + g3;               q0a= h3 - g3;
          s0 = (s0a * c0 + 0x7FFF) >> 16;
          q0 = (q0a * c0 + 0x7FFF) >> 16;

          P0 = p0 + p1;               P1 = p0 - p1;
          R1 = c6 * r1 + c2 * r0;     R0 = c6 * r0 - c2 * r1;

          Q1 = q1 + q0;               Q0 = q1 - q0;
          S1 = s1 + s0;               S0 = s1 - s0;

          F0 = P0;                    F4 = P1;
          F2 = R1;                    F6 = R0;

          F1 = c7 * Q1 + c1 * S1;     F7 = c7 * S1 - c1 * Q1;
          F5 = c3 * Q0 + c5 * S0;     F3 = c3 * S0 - c5 * Q0;

          data[ 0] = F0;
          data[ 8] = F1 >> 13;
          data[16] = F2 >> 13;
          data[24] = F3 >> 13;
          data[32] = F4;
          data[40] = F5 >> 13;
          data[48] = F6 >> 13;
          data[56] = F7 >> 13;

          data++;
      }
     

  data = dct_data;
  for (i = 0; i < 8 ; i++)
  {
      f0 = data[0];
      f1 = data[1];
      f2 = data[2];
      f3 = data[3];
      f4 = data[4];
      f5 = data[5];
      f6 = data[6];
      f7 = data[7];

      g0 = f0 + f7;               h2 = f0 - f7;
      g1 = f1 + f6;               h3 = f1 - f6;
      h1 = f2 + f5;               g3 = f2 - f5;
      h0 = f3 + f4;               g2 = f3 - f4;

      p0 = g0 + h0;               r0 = g0 - h0;
      p1 = g1 + h1;               r1 = g1 - h1;
      q1 = g2;                    s1 = h2;

      s0a= h3 + g3;               q0a= h3 - g3;
      q0 = (q0a * c0 + 0x7FFF) >> 16;
      s0 = (s0a * c0 + 0x7FFF) >> 16;

      P0 = p0 + p1;               P1 = p0 - p1;
      R1 = c6 * r1 + c2 * r0;     R0 = c6 * r0 - c2 * r1;

      Q1 = q1 + q0;               Q0 = q1 - q0;
      S1 = s1 + s0;               S0 = s1 - s0;

      F0 = P0;                    F4 = P1;
      F2 = R1;                    F6 = R0;

      F1 = c7 * Q1 + c1 * S1;     F7 = c7 * S1 - c1 * Q1;
      F5 = c3 * Q0 + c5 * S0;     F3 = c3 * S0 - c5 * Q0;

      F0r = (F0 + 0x0006) >>  3;
      F1r = (F1 + 0x7FFF) >> 16;
      F2r = (F2 + 0x7FFF) >> 16;
      F3r = (F3 + 0x7FFF) >> 16;
      F4r = (F4 + 0x0004) >>  3;
      F5r = (F5 + 0x7FFF) >> 16;
      F6r = (F6 + 0x7FFF) >> 16;
      F7r = (F7 + 0x7FFF) >> 16;

      data[0] = F0r;
      data[1] = F1r;
      data[2] = F2r;
      data[3] = F3r;
      data[4] = F4r;
      data[5] = F5r;
      data[6] = F6r;
      data[7] = F7r;

      data += 8;
  }

  return;
}