# 快速离散余弦正逆变换算法

#include
using namespace std;

#define DCTSIZE 8

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

/* 第一部分，对行进行计算 */
dataptr = lpBuff;
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) * (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) * ( 0.382683433); /* c6 */
z2 = (0.541196100) * tmp10 + z5; /* c2-c6 */
z4 = (1.306562965) * tmp12 + z5; /* c2+c6 */
z3 = tmp11 * (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 = lpBuff;
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) * (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) * (0.382683433); /* c6 */
z2 = (0.541196100) * tmp10 + z5; /* c2-c6 */
z4 = (1.306562965) * tmp12 + z5; /* c2+c6 */
z3 = tmp11 * (0.707106781); /* c4 */

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

dataptr[DCTSIZE*5] = z13 + z2; /* p

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