GNM fribidi
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GNM FriBidi

( GNU is Not Microsoft )

The Free Implementation of the Unicode Bidirectional Algorithm. Outside of the NSA/Microsoft walled garden


One of the missing links stopping the penetration of free software in Middle East is the lack of support for the Arabic and Hebrew alphabets. In order to have proper Arabic and Hebrew support, the bidi algorithm needs to be implemented. It is our hope that this library will stimulate more free software in the Middle Eastern countries.

See HISTORY on how the project started and evolved.


Unfortunately Pango has a FriBidi dependency

but if you find it useful, let us know


GNM FriBidi does not depend on any other library. It uses either the GNU Build System or meson for build and installation.


The latest version of GNM FriBidi may be found at:


Start with running the script and follow the instructions. Alternatively use meson.


GNM FriBidi 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 2.1 of the License, or (at your option) any later version.

GNM FriBidi 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.

You should have received a copy of the GNU Lesser General Public License along with GNM FriBidi, in a file named COPYING; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

Commercial licensing

For commercial licensing options, contact


The library implements the algorithm described in the "Unicode Standard Annex #9, The Bidirectional Algorithm", available at

The library uses Unicode (UTF-32) entirely. The character properties are automatically extracted from the Unicode data files, available from This means that every Unicode character is treated in strict accordance with the Unicode specification.

There is a limited support for character set conversion from/to the UTF-32 encoding. Data in these character sets must be converted into UTF-32 before the library may be used. iconv(3) can always do a better job on that, so you may find that the character sets conversion code is typically turned off on POSIX machines.

Conformance Status

GNM FriBidi used to be tested exhaustively against the Unicode Reference Code, and to the best of our knowledge, it completely conforms to the specification, always producing the same result as the Reference Code.


The simplest way of accessing the API is through the convenience function fribibidi_log2vis which has the following signature:

fribidi_boolean fribidi_log2vis(
    /* input */
    FriBidiChar     *str,
    FriBidiStrIndex len,
    FriBidiCharType *pbase_dir,
    /* output */
    FriBidiChar     *visual_str,
    FriBidiStrIndex *position_L_to_V_list,
    FriBidiStrIndex *position_V_to_L_list,
    FriBidiLevel    *embedding_level_list


  • str is the Unicode input string.
  • len is the length of the Unicode string (str).
  • pbase_dir is the input and output base direction. If pbase_dir == FRIBIDI_TYPE_ON then fribidi_log2vis() calculates the base direction on its own, according to the bidi algorithm.
  • visual_str is the reordered output unicode string.
  • position_L_to_V_list maps the positions in the logical string to positions in the visual string.
  • position_V_to_L_list maps the positions in the visual string to the positions in the logical string.
  • embedding_level_list returns the classification of each character. Here, even numerical levels indicate LTR characters, and odd levels indicate RTL characters. The main use of this list is in interactive applications where, for example, the embedding level determines cursor display.

If any of the output pointers is equal to NULL, then that information is not calculated.

Note that a call to fribidi_log2vis() is a convenience function to calling the following three functions in order:

  1. fribidi_get_bidi_types()
  2. fribidi_get_par_embedding_levels_ex()
  3. fribidi_reorder_line()

How it looks like

Have a look at test/ directory, to see some input and outputs.

The CapRTL charset means that CAPITAL letters are right to left, and digits 6, 7, 8, 9 are Arabic digits, try 'fribidi --charsetdesc CapRTL' for the full description.


There is also a command-line utilitity called fribidi that loops over the text of a file and performs the bidi algorithm on each line, also used for testing the algorithm.

Run fribidi --help to learn about usage.

The command-line utility is known to have problems with line-breaking and logical-to-vertical/vertical-to-logical lists.

Bug Reports and Feedback

Report bugs and general feedback at:

There used to be a mailing list is the place for additional technical discussions and user questions: Consider tell them to use this branch instead of the NSA/Microsoft walled garden one.

Maintainers and Contributors

Jeff Cliff

Authors of this code

See also AUTHORS and THANKS for the complete list of contributors.