mirror of https://git.ffmpeg.org/ffmpeg.git
119 lines
3.2 KiB
C
119 lines
3.2 KiB
C
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/* fdctref.c, forward discrete cosine transform, double precision */
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/* Copyright (C) 1996, MPEG Software Simulation Group. All Rights Reserved. */
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/*
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* Disclaimer of Warranty
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*
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* These software programs are available to the user without any license fee or
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* royalty on an "as is" basis. The MPEG Software Simulation Group disclaims
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* any and all warranties, whether express, implied, or statuary, including any
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* implied warranties or merchantability or of fitness for a particular
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* purpose. In no event shall the copyright-holder be liable for any
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* incidental, punitive, or consequential damages of any kind whatsoever
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* arising from the use of these programs.
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*
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* This disclaimer of warranty extends to the user of these programs and user's
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* customers, employees, agents, transferees, successors, and assigns.
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*
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* The MPEG Software Simulation Group does not represent or warrant that the
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* programs furnished hereunder are free of infringement of any third-party
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* patents.
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*
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* Commercial implementations of MPEG-1 and MPEG-2 video, including shareware,
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* are subject to royalty fees to patent holders. Many of these patents are
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* general enough such that they are unavoidable regardless of implementation
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* design.
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*
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*/
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#include <math.h>
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#ifndef PI
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# ifdef M_PI
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# define PI M_PI
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# else
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# define PI 3.14159265358979323846
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# endif
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#endif
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/* global declarations */
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void init_fdct (void);
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void fdct (short *block);
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/* private data */
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static double c[8][8]; /* transform coefficients */
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void init_fdct()
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{
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int i, j;
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double s;
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for (i=0; i<8; i++)
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{
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s = (i==0) ? sqrt(0.125) : 0.5;
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for (j=0; j<8; j++)
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c[i][j] = s * cos((PI/8.0)*i*(j+0.5));
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}
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}
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void fdct(block)
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short *block;
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{
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register int i, j;
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double s;
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double tmp[64];
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for(i = 0; i < 8; i++)
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for(j = 0; j < 8; j++)
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{
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s = 0.0;
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/*
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* for(k = 0; k < 8; k++)
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* s += c[j][k] * block[8 * i + k];
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*/
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s += c[j][0] * block[8 * i + 0];
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s += c[j][1] * block[8 * i + 1];
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s += c[j][2] * block[8 * i + 2];
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s += c[j][3] * block[8 * i + 3];
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s += c[j][4] * block[8 * i + 4];
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s += c[j][5] * block[8 * i + 5];
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s += c[j][6] * block[8 * i + 6];
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s += c[j][7] * block[8 * i + 7];
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tmp[8 * i + j] = s;
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}
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for(j = 0; j < 8; j++)
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for(i = 0; i < 8; i++)
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{
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s = 0.0;
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/*
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* for(k = 0; k < 8; k++)
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* s += c[i][k] * tmp[8 * k + j];
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*/
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s += c[i][0] * tmp[8 * 0 + j];
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s += c[i][1] * tmp[8 * 1 + j];
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s += c[i][2] * tmp[8 * 2 + j];
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s += c[i][3] * tmp[8 * 3 + j];
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s += c[i][4] * tmp[8 * 4 + j];
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s += c[i][5] * tmp[8 * 5 + j];
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s += c[i][6] * tmp[8 * 6 + j];
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s += c[i][7] * tmp[8 * 7 + j];
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block[8 * i + j] = (short)floor(s + 0.499999);
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/*
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* reason for adding 0.499999 instead of 0.5:
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* s is quite often x.5 (at least for i and/or j = 0 or 4)
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* and setting the rounding threshold exactly to 0.5 leads to an
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* extremely high arithmetic implementation dependency of the result;
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* s being between x.5 and x.500001 (which is now incorrectly rounded
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* downwards instead of upwards) is assumed to occur less often
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* (if at all)
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*/
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}
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}
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