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read_24bit.c
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Fri, Jul 18, 08:43

read_24bit.c
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/*
* Copyright (C) 2006, Robert Oostenveld, F.C. Donders Ccentre for Cognitive Neuroimaging
* Copyright (C) 2007, Peter Desain, Nijmegen Institute for Cognition and Information
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
*
* $Id: read_24bit.c 7123 2012-12-06 21:21:38Z roboos $
*/
/*
* _LARGEFILE_SOURCE takes care that the offset is represented as 64 bit on supported platforms
* it should be defined prior to including the system header files
*/
#define _LARGEFILE_SOURCE
#include <math.h>
#include <sys/types.h>
#include "mex.h"
#include "matrix.h"
#if defined(_WIN32) || defined(_WIN64)
#define int32_t INT32_T
#define int64_t INT64_T
#define fseeko fseek
#else
#include <stdint.h>
#endif
void
mexFunction (int nlhs, mxArray * plhs[], int nrhs, const mxArray * prhs[])
{
FILE *fp;
mxArray *dat;
double *dat_p;
char *filename, *buf;
int32_t fnlen, b1, b2, b3;
/* these have to be able to handle large files (>2GB) on supported platforms */
int64_t count, indx;
size_t num, numwords;
off_t offset;
if (nrhs != 3)
mexErrMsgTxt ("Invalid number of input arguments");
if (mxGetM(prhs[1])!=1 || mxGetN(prhs[1])!=1)
mexErrMsgTxt ("Invalid dimension for input argument 2");
if (mxGetM(prhs[2])!=1 || mxGetN(prhs[2])!=1)
mexErrMsgTxt ("Invalid dimension for input argument 3");
/* get the filename */
fnlen = mxGetN(prhs[0]);
filename = mxCalloc(fnlen+1, sizeof(char));
mxGetString(prhs[0], filename, fnlen+1);
/* get values and typecast to integer */
offset = (off_t)(mxGetScalar (prhs[1]));
numwords = (off_t)(mxGetScalar (prhs[2]));
/*
printf("filename = %s\n", filename);
printf("fnlen = %d\n", fnlen);
printf("offset = %d\n", offset);
printf("numwords = %d\n", numwords);
*/
/* open the file and read the desired bytes */
fp = fopen(filename, "rb");
if (fp==NULL)
{
printf("error opening file: %s\n", filename);
return;
}
fseeko(fp, offset, SEEK_SET);
buf = mxCalloc(3*numwords, sizeof(char));
count = fread(buf, sizeof(char), 3*numwords, fp);
if (count<3*numwords)
{
printf("error reading from %s\n", filename);
fclose(fp);
return;
}
else
{
fclose(fp);
}
/* convert every thee bytes into one word */
dat = mxCreateDoubleMatrix (1, numwords, mxREAL);
dat_p = mxGetData (dat);
for (count=0; count<numwords; count++)
{
indx = count*3;
b1 = (0x000000FF & ((int32_t)buf[indx ]));
b2 = (0x000000FF & ((int32_t)buf[indx+1]));
b3 = (0x000000FF & ((int32_t)buf[indx+2]));
dat_p[count] = ((int32_t) ((b3 << 24) | (b2 << 16) | (b1 << 8)))/256;
}
/* explicitely free the buffer memory and don't wait for the garbage collector */
mxFree(buf);
/* assign the output parameters */
plhs[0] = dat;
return;
}

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