pcompress/transpose/transpose.c

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/*
* This file is a part of Pcompress, a chunked parallel multi-
* algorithm lossless compression and decompression program.
*
* Copyright (C) 2012 Moinak Ghosh. All rights reserved.
* Use is subject to license terms.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 3 of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* moinakg@belenix.org, http://moinakg.wordpress.com/
*/
#include "transpose.h"
/*
* Perform a simple matrix transpose of the given buffer in "from".
* If the buffer contains tables of numbers or structured data a
* transpose can potentially help improve compression ratio by
* bringing repeating values in columns into row ordering.
*/
void
transpose(unsigned char *from, unsigned char *to, uint64_t buflen, uint64_t stride, rowcol_t rc)
{
uint64_t rows, cols, i, j, k, l;
if (rc == ROW) {
rows = buflen / stride;
cols = stride;
} else {
cols = buflen / stride;
rows = stride;
}
k = 0;
for (j = 0; j < rows; j++) {
l = 0;
for (i = 0; i < cols; i++) {
to[j + l] = from[i + k];
l += rows;
}
k += cols;
}
}