fast DCT

// Run this once before running the fastDCT for the first time // This function creates contants (M_PI means pi) int initFastDCT(float* c) { c[0] = cos(M_PI * 0.0625); c[1] = cos(M_PI * 0.125); c[2] = cos(M_PI * 0.1875); c[3] = cos(M_PI * 0.25); c[4] = cos(M_PI * 0.3125); c[5] = cos(M_PI * 0.375); c[6] = cos(M_PI * 0.4375); // two consts as scalars c[7] = sqrt(.125); // for k0 c[8] = sqrt(.25); // for the rest c[9] = sqrt(.5); // for idct return 1; } // n is input of 8 values (between -1 and + 1) // o is out // c are the constants created on the previous function int fastDct(float* n,float* o,float* c) { // the q's float q1 = n[0]-n[7]; float q2 = n[1]-n[6]; float q3 = n[2]-n[5]; float q4 = n[3]-n[4]; float q5 = n[0]+n[7]; float q6 = n[1]+n[6]; float q7 = n[2]+n[5]; float q8 = n[3]+n[4]; float q9 = q5+q8; float q10 = q6+q7; float q11 = q5-q8; float q12 = q6-q7; o[0] = c[7]*(q9+q10); o[1] = c[8]*(c[0]*q1+c[2]*q2+c[4]*q3+c[6]*q4); o[2] = c[8]*(c[1]*q11+c[5]*q12); o[3] = c[8]*(c[2]*q1-c[6]*q2-c[0]*q3-c[4]*q4); o[4] = c[8]*c[3]*(q9-q10); o[5] = c[8]*(c[4]*q1-c[0]*q2+c[6]*q3+c[2]*q4); o[6] = c[8]*(c[5]*q11-c[1]*q12); o[7] = c[8]*(c[6]*q1-c[4]*q2+c[2]*q3-c[0]*q4); return 1; }