# EDFlib

EDFlib is a programming library for C/C++ for reading and writing EDF+ and BDF+ files.
It also reads "old style" EDF and BDF files.
EDF means European Data Format. BDF is the 24-bits version of EDF.


## Usage

The library consists of only two files: `edflib.h` and `edflib.c`.

In order to use EDFlib, copy these two files to your project.
Include the file `edflib.h` in every source file from where you want to access the library.

Don't forget to tell your compiler that it must compile and link `edflib.c` (add it to
your makefile or buildscript). `edflib.c` needs to be compiled with the options
`-D_LARGEFILE64_SOURCE -D_LARGEFILE_SOURCE`.

For example:

`gcc -Wall -Wextra -Wshadow -Wformat-nonliteral -Wformat-security -D_LARGEFILE64_SOURCE -D_LARGEFILE_SOURCE test_edflib.c edflib.c -lm -o test_edflib`

Compilation has been tested using GCC on Linux, Mingw-w64 on Windows, and LLVM GCC on OS X (Yosemite).

Big-endian systems are not supported.

To understand how to use the library, read the comments in `edflib.h`.


## Examples

To build the examples: `make`

Each "generator" example creates an EDF+ or BDF+ file with sample signals.

`test_generator` shows how to use most of the functions provided by the library and generates an
EDF+ or BDF+ testfile with several sample signals.

`sine_generator` creates a BDF+ file containing the signal "sine", a 1 Hz sinoidal waveform with a
sample frequency of 2048 Hz.

`sweep_generator` creates a linear or logarithmic sweep through a range of frequencies in EDF+ or
BDF+ format.

Use EDFbrowser to view these files: http://www.teuniz.net/edfbrowser/

`test_edflib <filename> <signalnumber>` will print the properties of the EDF/BDF header, the
annotations, and the values of 200 samples of the chosen signal. For example, running
`test_generator` will produce the file `test_generator.edf`. Running `test_edflib test_generator.edf 6`
will show the header and first 200 samples of the "noise" signal:
`75  6  27  77  37  30  35  96  62  69  34  15  51  56  69  68  80  45 ...`

## Background info

In EDF, the sensitivity (e.g. uV/bit) and offset are stored using four parameters:
digital maximum and minimum, and physical maximum and minimum.
Here, digital means the raw data coming from a sensor or ADC. Physical means the units like uV.
The sensitivity in units/bit is calculated as follows:

units per bit = (physical max - physical min) / (digital max - digital min)

The digital offset is calculated as follows:

offset = (physical max / units per bit) - digital max

For a better explanation about the relation between digital data and physical data,
read the document "Coding Schemes Used with Data Converters" (PDF):

http://www.ti.com/general/docs/lit/getliterature.tsp?baseLiteratureNumber=sbaa042

An EDF file usually contains multiple so-called datarecords. One datarecord usually has a duration of one second (this is the default but it is not mandatory!).
In that case a file with a duration of five minutes contains 300 datarecords. The duration of a datarecord can be freely choosen but, if possible, use values from
0.1 to 1 second for easier handling. Just make sure that the total size of one datarecord, expressed in bytes, does not exceed 10MByte (15MBytes for BDF(+)).

The RECOMMENDATION of a maximum datarecordsize of 61440 bytes in the EDF and EDF+ specification was usefull in the time people were still using DOS as their main operating system.
Using DOS and fast (near) pointers (16-bit pointers), the maximum allocatable block of memory was 64KByte.
This is not a concern anymore so the maximum datarecord size now is limited to 10MByte for EDF(+) and 15MByte for BDF(+). This helps to accommodate for higher samplingrates
used by modern Analog to Digital Converters.

EDF header character encoding: The EDF specification says that only ASCII characters are allowed.
EDFlib will automatically convert characters with accents, umlauts, tilde, etc. to their "normal" equivalent without the accent/umlaut/tilde/etc.

The description/name of an EDF+ annotation on the other hand, is encoded in UTF-8.


## License

Copyright (c) 2009 - 2020 Teunis van Beelen
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

* Redistributions of source code must retain the above copyright notice, this
  list of conditions and the following disclaimer.

* Redistributions in binary form must reproduce the above copyright notice,
  this list of conditions and the following disclaimer in the documentation
  and/or other materials provided with the distribution.

* Neither the name of the copyright holder nor the names of its
  contributors may be used to endorse or promote products derived from
  this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
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SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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