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103 lines
2.7 KiB
C
103 lines
2.7 KiB
C
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/* Reference_IDCT.c, Inverse Discrete Fourier 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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/* Perform IEEE 1180 reference (64-bit floating point, separable 8x1
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* direct matrix multiply) Inverse Discrete Cosine Transform
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*/
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/* Here we use math.h to generate constants. Compiler results may
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vary a little */
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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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/* private data */
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/* cosine transform matrix for 8x1 IDCT */
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static double gst_idct_float_c[8][8];
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/* initialize DCT coefficient matrix */
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void gst_idct_init_float_idct()
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{
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int freq, time;
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double scale;
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for (freq=0; freq < 8; freq++)
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{
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scale = (freq == 0) ? sqrt(0.125) : 0.5;
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for (time=0; time<8; time++)
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gst_idct_float_c[freq][time] = scale*cos((PI/8.0)*freq*(time + 0.5));
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}
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}
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/* perform IDCT matrix multiply for 8x8 coefficient block */
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void gst_idct_float_idct(block)
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short *block;
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{
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int i, j, k, v;
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double partial_product;
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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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partial_product = 0.0;
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for (k=0; k<8; k++)
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partial_product+= gst_idct_float_c[k][j]*block[8*i+k];
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tmp[8*i+j] = partial_product;
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}
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/* Transpose operation is integrated into address mapping by switching
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loop order of i and j */
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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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partial_product = 0.0;
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for (k=0; k<8; k++)
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partial_product+= gst_idct_float_c[k][i]*tmp[8*k+j];
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v = (int) floor(partial_product+0.5);
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block[8*i+j] = (v<-256) ? -256 : ((v>255) ? 255 : v);
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}
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}
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