jfdctflt.c

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/*
 * jfdctflt.c
 *
 *该文件为前向DCT的浮点运算，它要比整数运算更精确。 
 *
 
 */

#ifdef DCT_FLOAT_SUPPORTED


/*
/*该程序只适用于8×8的块变换*/	

#if DCTSIZE != 8
  Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
#endif



/* 在一个采样块上进行DCT变换 */

GLOBAL(void)
jpeg_fdct_float (FAST_FLOAT * data)
{
  FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
  FAST_FLOAT tmp10, tmp11, tmp12, tmp13;
  FAST_FLOAT z1, z2, z3, z4, z5, z11, z13;
  FAST_FLOAT *dataptr;
  int ctr;

/* 第一部分，对行进行计算 */
  dataptr = data;
  for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
    tmp0 = dataptr[0] + dataptr[7];
    tmp7 = dataptr[0] - dataptr[7];
    tmp1 = dataptr[1] + dataptr[6];
    tmp6 = dataptr[1] - dataptr[6];
    tmp2 = dataptr[2] + dataptr[5];
    tmp5 = dataptr[2] - dataptr[5];
    tmp3 = dataptr[3] + dataptr[4];
    tmp4 = dataptr[3] - dataptr[4];
    
/* 对偶数项进行运算 */    
    tmp10 = tmp0 + tmp3;	/* phase 2 */
    tmp13 = tmp0 - tmp3;
    tmp11 = tmp1 + tmp2;
    tmp12 = tmp1 - tmp2;
    
    dataptr[0] = tmp10 + tmp11; /* phase 3 */
    dataptr[4] = tmp10 - tmp11;
    
    z1 = (tmp12 + tmp13) * ((FAST_FLOAT) 0.707106781); /* c4 */
    dataptr[2] = tmp13 + z1;	/* phase 5 */
    dataptr[6] = tmp13 - z1;
    
/* 对奇数项进行计算 */
    tmp10 = tmp4 + tmp5;	/* phase 2 */
    tmp11 = tmp5 + tmp6;
    tmp12 = tmp6 + tmp7;

    z5 = (tmp10 - tmp12) * ((FAST_FLOAT) 0.382683433); /* c6 */
    z2 = ((FAST_FLOAT) 0.541196100) * tmp10 + z5; /* c2-c6 */
    z4 = ((FAST_FLOAT) 1.306562965) * tmp12 + z5; /* c2+c6 */
    z3 = tmp11 * ((FAST_FLOAT) 0.707106781); /* c4 */

    z11 = tmp7 + z3;		/* phase 5 */
    z13 = tmp7 - z3;

    dataptr[5] = z13 + z2;	/* phase 6 */
    dataptr[3] = z13 - z2;
    dataptr[1] = z11 + z4;
    dataptr[7] = z11 - z4;

    dataptr += DCTSIZE;	/* 将指针指向下一行 */
  }

/* 第二部分，对列进行计算 */
  dataptr = data;
  for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
    tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*7];
    tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7];
    tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6];
    tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6];
    tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5];
    tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5];
    tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4];
    tmp4 = dataptr[DCTSIZE*3] - dataptr[DCTSIZE*4];
    
/* 对偶数项进行运算 */    
    tmp10 = tmp0 + tmp3;	/* phase 2 */
    tmp13 = tmp0 - tmp3;
    tmp11 = tmp1 + tmp2;
    tmp12 = tmp1 - tmp2;
    
    dataptr[DCTSIZE*0] = tmp10 + tmp11; /* phase 3 */
    dataptr[DCTSIZE*4] = tmp10 - tmp11;
    
    z1 = (tmp12 + tmp13) * ((FAST_FLOAT) 0.707106781); /* c4 */
    dataptr[DCTSIZE*2] = tmp13 + z1; /* phase 5 */
    dataptr[DCTSIZE*6] = tmp13 - z1;
    
/* 对奇数项进行计算 */
    tmp10 = tmp4 + tmp5;	/* phase 2 */
    tmp11 = tmp5 + tmp6;
    tmp12 = tmp6 + tmp7;

    z5 = (tmp10 - tmp12) * ((FAST_FLOAT) 0.382683433); /* c6 */
    z2 = ((FAST_FLOAT) 0.541196100) * tmp10 + z5; /* c2-c6 */
    z4 = ((FAST_FLOAT) 1.306562965) * tmp12 + z5; /* c2+c6 */
    z3 = tmp11 * ((FAST_FLOAT) 0.707106781); /* c4 */

    z11 = tmp7 + z3;		/* phase 5 */
    z13 = tmp7 - z3;

    dataptr[DCTSIZE*5] = z13 + z2; /* phase 6 */
    dataptr[DCTSIZE*3] = z13 - z2;
    dataptr[DCTSIZE*1] = z11 + z4;
    dataptr[DCTSIZE*7] = z11 - z4;

    dataptr++;			/* 将指针指向下一列 */
}

#endif /* DCT_FLOAT_SUPPORTED */