/* fdctref.c, forward discrete cosine transform, double precision */ /* Copyright (C) 1996, MPEG Software Simulation Group. All Rights Reserved. */ /* * Disclaimer of Warranty * * These software programs are available to the user without any license fee or * royalty on an "as is" basis. The MPEG Software Simulation Group disclaims * any and all warranties, whether express, implied, or statuary, including any * implied warranties or merchantability or of fitness for a particular * purpose. In no event shall the copyright-holder be liable for any * incidental, punitive, or consequential damages of any kind whatsoever * arising from the use of these programs. * * This disclaimer of warranty extends to the user of these programs and user's * customers, employees, agents, transferees, successors, and assigns. * * The MPEG Software Simulation Group does not represent or warrant that the * programs furnished hereunder are free of infringement of any third-party * patents. * * Commercial implementations of MPEG-1 and MPEG-2 video, including shareware, * are subject to royalty fees to patent holders. Many of these patents are * general enough such that they are unavoidable regardless of implementation * design. * */ #include <math.h> #include "mpegintf.H" #ifndef PI # ifdef M_PI # define PI M_PI # else # define PI 3.14159265358979323846 # endif #endif /* private data */ static double c[8][8]; /* transform coefficients */ void MPEG::init_fdct() { int i, j; double s; for (i=0; i<8; i++) { s = (i==0) ? sqrt(0.125) : 0.5; for (j=0; j<8; j++) c[i][j] = s * cos((PI/8.0)*i*(j+0.5)); } } void MPEG::fdct(short *block) { int i, j, k; double s; double tmp[64]; for (i=0; i<8; i++) for (j=0; j<8; j++) { s = 0.0; for (k=0; k<8; k++) s += c[j][k] * block[8*i+k]; tmp[8*i+j] = s; } for (j=0; j<8; j++) for (i=0; i<8; i++) { s = 0.0; for (k=0; k<8; k++) s += c[i][k] * tmp[8*k+j]; block[8*i+j] = (int)floor(s+0.499999); /* * reason for adding 0.499999 instead of 0.5: * s is quite often x.5 (at least for i and/or j = 0 or 4) * and setting the rounding threshold exactly to 0.5 leads to an * extremely high arithmetic implementation dependency of the result; * s being between x.5 and x.500001 (which is now incorrectly rounded * downwards instead of upwards) is assumed to occur less often * (if at all) */ } }

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