C Programming Language
======================

Learning C
----------

-  **The best way to learn programming is, always, writing your own
   code!**

-  `Why Code in C Anymore?….Instead of
   C++ <http://www.drdobbs.com/cpp/why-code-in-c-anymore/240149452>`__

   -  C still has a little advantage on the performance and portability.

-  `CS2022: Introduction to C at
   Cornell <http://www.cs.cornell.edu/courses/cs2022/2011sp/>`__

   -  Lecture slides are available.

-  `learn-c.org free interactive C
   tutorial <https://www.learn-c.org/>`__

-  `30-seconds-of-c <https://github.com/fredsiika/30-seconds-of-c>`__

   -  Curated collection of useful C Programming tutorials, snippets,
      and projects that you can understand in 30 seconds or less

Useful Libraries
----------------

Performance
~~~~~~~~~~~

-  `Optimization of Computer Programs in
   C <http://icps.u-strasbg.fr/~bastoul/local_copies/lee.html>`__

   -  By Michael Lee. “It focuses on minimizing time spent by the CPU
      and gives sample source code transformations that often yield
      improvements. Memory and I/O speed improvements are also
      discussed.”

-  `Tips for Optimizing C/C++
   Code <https://people.cs.clemson.edu/~dhouse/courses/405/papers/optimize.pdf>`__

   -  Very practical and useful guides for optimizing C/C++.

-  `mimalloc - mimalloc is a compact general purpose allocator with
   excellent performance <https://github.com/microsoft/mimalloc>`__

   -  By Microsoft. mimalloc (pronounced “me-malloc”) is a general
      purpose allocator with excellent performance characteristics. It
      is a drop-in replacement for malloc and can be used in other
      programs without code changes.

Numerical
~~~~~~~~~

-  `GSL - GNU Scientific Library <https://www.gnu.org/software/gsl/>`__

   -  The library provides a wide range of mathematical routines such as
      random number generators, special functions and least-squares
      fitting. There are over 1000 functions in total with an extensive
      test suite.
   -  The `online reference manual can be found
      here <https://www.gnu.org/software/gsl/doc/html/index.html>`__.

-  `FFTW <http://www.fftw.org/>`__

   -  **FFTW** is a C subroutine library for computing the discrete
      Fourier transform (DFT) in one or more dimensions, of arbitrary
      input size, and of both real and complex data (as well as of
      even/odd data, i.e. the discrete cosine/sine transforms or
      DCT/DST).
   -  The `online manual can be found
      here <http://fftw.org/fftw3_doc/>`__

Astronomy Related
~~~~~~~~~~~~~~~~~

-  `cfitsio - ANSI C routines for reading and writing FITS format data
   files <https://github.com/healpy/cfitsio>`__

Specific Topics
---------------

Multiprocessing
~~~~~~~~~~~~~~~

GPU Enhancement
~~~~~~~~~~~~~~~

Code to Study
-------------

-  `sextractor - Extract catalogs of sources from astronomical
   images <https://github.com/astromatic/sextractor>`__

-  `psfex - Generate PSF super-tabulated
   models <https://github.com/astromatic/psfex>`__

-  `CCL - DESC Core Cosmology
   Library <https://github.com/LSSTDESC/CCL>`__

   -  Also teaches you how to interact with Python.

-  `Corrfunc - fast correlation functions on the
   CPU <https://github.com/manodeep/Corrfunc>`__

   -  **utils** are written in C; and wrapped in Python.

On Interacting with Python
~~~~~~~~~~~~~~~~~~~~~~~~~~

-  `sep - Python and C library for source extraction and
   photometry <https://github.com/kbarbary/sep>`__

   -  Using **Cython**.

-  `cosmology - Some code for calculating cosmological
   distances <https://github.com/esheldon/cosmology>`__

   -  By Erin Sheldon. Using **CPython**

-  `smatch - Code to match points on the sphere using the healpix
   scheme <https://github.com/esheldon/smatch>`__

   -  By Erin Sheldon. Using **CPython**