77 lines
1.8 KiB
C++
77 lines
1.8 KiB
C++
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/*
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Burrows–Wheeler Transform.
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The code in this file is based on TheUnarchiver.
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See README.md and docs/licenses/TheUnarchiver.txt for more information.
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Copyright (C) 2019, Guillaume Gonnet
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This program is free software: you can redistribute it and/or modify it under
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the terms of the GNU General Public License as published by the Free Software
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Foundation, either version 3 of the License, or (at your option) any later
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version.
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This program is distributed in the hope that it will be useful, but WITHOUT ANY
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WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
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PARTICULAR PURPOSE. See the GNU General Public License for more details.
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You should have received a copy of the GNU General Public License along with
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this program. If not, see <https://www.gnu.org/licenses/>.
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*/
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#include "stuffit/utils/bwt.h"
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namespace maconv {
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namespace stuffit {
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// Calculate inverse of BWT.
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void CalculateInverseBWT(uint32_t *transform, uint8_t *block, int block_len)
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{
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int counts[256] = {0};
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int cumulative_counts[256];
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for (int i = 0; i < block_len; i++)
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counts[block[i]]++;
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for (int i = 0, total = 0; i < 256; i++) {
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cumulative_counts[i] = total;
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total += counts[i];
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counts[i] = 0;
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}
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for (int i = 0; i < block_len; i++) {
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transform[cumulative_counts[block[i]] + counts[block[i]]] = i;
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counts[block[i]]++;
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}
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}
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// Reset the decoder.
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void MtfDecoder::ResetDecoder()
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{
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for (int i = 0; i < 256; i++)
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table[i] = i;
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}
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// Decode the next symbol.
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int MtfDecoder::Decode(int symbol)
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{
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int res = table[symbol];
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for (int i = symbol; i > 0; i--)
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table[i] = table[i-1];
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table[0] = res;
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return res;
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}
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} // namespace stuffit
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} // namespace maconv
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