107 lines
4.8 KiB
C
107 lines
4.8 KiB
C
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/*-*- mode:c;indent-tabs-mode:t;c-basic-offset:4;tab-width:4;coding:utf-8 -*-│
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│vi: set et ft=c ts=4 sw=4 fenc=utf-8 :vi│
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ PL_MPEG - MPEG1 Video decoder, MP2 Audio decoder, MPEG-PS demuxer │
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│ Dominic Szablewski - https://phoboslab.org │
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│ │
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│ The MIT License(MIT) │
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│ Copyright(c) 2019 Dominic Szablewski │
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│ │
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│ Permission is hereby granted, free of charge, to any person obtaining │
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│ a copy of this software and associated documentation files(the │
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│ "Software"), to deal in the Software without restriction, including │
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│ without limitation the rights to use, copy, modify, merge, publish, │
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│ distribute, sublicense, and / or sell copies of the Software, and to │
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│ permit persons to whom the Software is furnished to do so, subject to │
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│ the following conditions: │
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│ │
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│ The above copyright notice and this permission notice shall be │
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│ included in all copies or substantial portions of the Software. │
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│ │
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│ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, │
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│ EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF │
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│ MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND │
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│ NONINFRINGEMENT.IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE │
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│ LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN │
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│ ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN │
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│ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE │
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│ SOFTWARE. │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "dsp/core/half.h"
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asm(".ident\t\"\\n\\n\
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PL_MPEG (MIT License)\\n\
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Copyright(c) 2019 Dominic Szablewski\\n\
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https://phoboslab.org\"");
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asm(".include \"libc/disclaimer.inc\"");
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/**
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* Computes Fixed-Point 8x8 Inverse Discrete Cosine Transform.
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*
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* @note discovered by Nasir Ahmed
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*/
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void plm_video_idct(int block[8][8]) {
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int i, j, t1, t2, m0;
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int b1, b3, b4, b6, b7;
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int y3, y4, y5, y6, y7;
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int x0, x1, x2, x3, x4;
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for (i = 0; i < 8; ++i) {
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b1 = block[4][i];
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b3 = block[2][i] + block[6][i];
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b4 = block[5][i] - block[3][i];
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t1 = block[1][i] + block[7][i];
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t2 = block[3][i] + block[5][i];
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b6 = block[1][i] - block[7][i];
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b7 = t1 + t2;
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m0 = block[0][i];
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x4 = ((b6 * 473 - b4 * 196 + 128) >> 8) - b7;
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x0 = x4 - (((t1 - t2) * 362 + 128) >> 8);
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x1 = m0 - b1;
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x2 = (((block[2][i] - block[6][i]) * 362 + 128) >> 8) - b3;
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x3 = m0 + b1;
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y3 = x1 + x2;
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y4 = x3 + b3;
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y5 = x1 - x2;
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y6 = x3 - b3;
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y7 = -x0 - ((b4 * 473 + b6 * 196 + 128) >> 8);
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block[0][i] = b7 + y4;
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block[1][i] = x4 + y3;
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block[2][i] = y5 - x0;
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block[3][i] = y6 - y7;
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block[4][i] = y6 + y7;
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block[5][i] = x0 + y5;
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block[6][i] = y3 - x4;
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block[7][i] = y4 - b7;
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}
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for (i = 0; i < 8; ++i) {
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b1 = block[i][4];
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b3 = block[i][2] + block[i][6];
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b4 = block[i][5] - block[i][3];
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t1 = block[i][1] + block[i][7];
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t2 = block[i][3] + block[i][5];
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b6 = block[i][1] - block[i][7];
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b7 = t1 + t2;
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m0 = block[i][0];
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x4 = ((b6 * 473 - b4 * 196 + 128) >> 8) - b7;
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x0 = x4 - (((t1 - t2) * 362 + 128) >> 8);
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x1 = m0 - b1;
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x2 = (((block[i][2] - block[i][6]) * 362 + 128) >> 8) - b3;
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x3 = m0 + b1;
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y3 = x1 + x2;
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y4 = x3 + b3;
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y5 = x1 - x2;
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y6 = x3 - b3;
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y7 = -x0 - ((b4 * 473 + b6 * 196 + 128) >> 8);
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block[i][0] = (b7 + y4 + 128) >> 8;
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block[i][1] = (x4 + y3 + 128) >> 8;
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block[i][2] = (y5 - x0 + 128) >> 8;
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block[i][3] = (y6 - y7 + 128) >> 8;
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block[i][4] = (y6 + y7 + 128) >> 8;
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block[i][5] = (x0 + y5 + 128) >> 8;
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block[i][6] = (y3 - x4 + 128) >> 8;
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block[i][7] = (y4 - b7 + 128) >> 8;
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}
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}
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