# Overview

==============================================================
PDCLib - the Public Domain C Library <http://pdclib.e43.eu>_
==============================================================

What is it
==========

This is a C Standard Library - what's defined in ISO/IEC 9899 "Information
technology — Programming languages — C" or extensions to the above defined in
ISO/IEC 14882 "Information technology — Programming languages — C++". A few
extensions may optionally be provided.

=======

Written in
* 2003-2012 by Martin "Solar" Baute,
* 2012-     by Owen Shepherd

To the extent possible under law, the author(s) have dedicated all copyright
and related and neighboring rights to this software to the public domain
worldwide. This software is distributed without any warranty.

You should have received a copy of the CC0 Public Domain Dedication along with
this software. If not, see <http://creativecommons.org/publicdomain/zero/1.0/>.

Exceptions
----------

Unicode Character Data
~~~~~~~~~~~~~~~~~~~~~~
PDCLib necessarily includes Unicode character data derived from that provided by
Unicode, Inc in its' implementation of the localization and wide character
support (in particular for use by the ctype.h and wctype.h functions.)

Unicode, Inc licenses that data under a license agreement which can be found at
UNICODE_DATA_LICENSE.txt. found in the same directory as this file.

Test Suite
~~~~~~~~~~
Portions of the test suite are under different licenses. Where this is the case,
it is clearly noted in the relevant location.

The license of this code has no bearing upon the licensing of the built library
(as it does not comprise part of it).

At the time this was written, this exception only applies to portions of the
printf test suite, which are released under the terms of the 2-clause BSD
license (see testing/printf_testcases.h for full details)

Terms for extensions
====================
Extensions are permitted only if they pass the following tests:

Pre-existing wide usage
On most systems, the system C library must maintain its application binary
interface for long periods of time (potentially eternity). Existing wide
usage demonstrates utility

In keeping with the spirit of the standard
The extension should respect the design, intentions and conventions of the C
standard, and feel like a natural extension to the offered capability.

Not system dependent
system

Non-duplicative
Extensions should not duplicate functionality already provided by the
standard

Disabled by default
PDCLib will always default to a "strictly conforming" mode exposing only
functionality offered by the version of the standard specified by the
__STDC_VERSION__, __STDC__ or __cplusplus macro; extensions will only be
exposed when requested.

Additionally, extra consideration will be given to extensions which are
the C library.

Conrete Examples:

strndup
**Included.** strndup is easily defined in terms of existing standard
functions, follows  the standard's naming conventions, is in wide usage, and
does not duplicate  features already provided.

posix_memalign
**Rejected.** Has existing wide usage, is not system dependent (can be
implemented, albeit inefficiently, on top of malloc), but naming is not
consistent with the naming used by the standard (posix_ prefix) and
duplicates functionality provided by the C11 standard

**Rejected.** Widely used, but duplicates functionality provided by the
standard (FILE objects set to be unbuffered), and not able to implement full
semantics (e.g. in relation to POSIX fork and other functionality from the
same defining standard) in a platform-neutral way

strl*
**Rejected.** Used somewhat widely, in keeping with the standard, not system
dependent, but duplicative of functionality provided by (optional) Annex K
of the C standard.

flockfile, funlockfile, getc_unlocked, putc_unlocked, fwrite_unlocked, ...
**Accepted.** Provide functionality not provided by the standard (and
useful in light of the C11 addition of threading). Can be trivially
implemented in terms of the <threads.h> mutex functions and the bodies of
the existing I/O functions, and impossible to implement externally

Internals
=========

As a namespace convention, everything (files, typedefs, functions,
macros) not defined in ISO/IEC 9899 is prefixed with _PDCLIB.
The standard defines any identifiers starting with '_' and a capital
letter as reserved for the implementation, and since the chances of
your compiler using an identifier in the _PDCLIB range are slim,
any strictly conforming application should work with this library.

PDCLib consists of several parts:

2) implementation files for standard functions;
3) internal header files keeping complex stuff out of the standard
4) the central, platform-specific file _PDCLIB_config.h;
5) platform-specific implementation files;

The standard headers (in ./includes/) only contain what they are
defined to contain. Where additional logic or macro magic is
necessary, that is deferred to the internal files. This has been done
so that the headers are actually educational as to what they provide
(as opposed to how the library does it).

There is a seperate implementation file (in ./function/{header}/) for
every function defined by the standard, named {function}.c. Not only
does this avoid linking in huge amounts of unused code when you use
but a single function, it also allows the optimization overlay to work
(see below).

(The directory ./functions/_PDCLIB/ contains internal and helper
functions that are not part of the standard.)

Then there are internal header files (in ./internal/), which contain
all the "black magic" and "code fu" that was kept out of the standard
headers. You should not have to touch them if you want to adapt PDCLib
to a new platform. Note that, if you *do* have to touch them, I would
consider it a serious design flaw, and would be happy to fix it in the
next PDCLib release. Any adaption work should be covered by the steps
detailed below.

For adapting PDCLib to a new platform (the trinity of CPU, operating
system, and compiler), make a copy of ./platform/example/ named
./platform/{your_platform}/, and modify the files of your copy to suit
the constraints of your platform. When you are done, copy the contents
of your platform directory over the source directory structure
of PDCLib (or link them into the appropriate places). That should be
all that is actually required to make PDCLib work for your platform.

Future directions
=================
Obviously, full C89, C99 and C11 conformance; and full support for the
applicable portions of C++98, C++03 and C++11 (the version which acomplishes
this will be christened "1.0").

Support for "optimization overlays." These would allow efficient
implementations of certain functions on individual platforms, for example
memcpy, strcpy and memset. This requires further work to only compile in one
version of a given function.

Post 1.0, support for C11 Annexe K "Bounds checking interfaces"

Development Status
==================

v0.1 - 2004-12-12
Freestanding-only C99 implementation without any overlay, and missing
the INTN_C() / UINTN_C() macros. <float.h> still has the enquire.c
values hardcoded into it; not sure whether to include enquire.c in the
package, to leave <float.h> to the overlay, or devise some parameterized
macro magic as for <limits.h> / <stdint.h>. Not thoroughly tested, but
I had to make the 0.1 release sometime so why not now.

v0.2 - 2005-01-12
Adds implementations for <string.h> (excluding strerror()), INTN_C() /
UINTN_C() macros, and some improvements in the internal headers.

v0.3 - 2005-11-21
Adds test drivers, fixes some bugs in <string.h>.

v0.4 - 2005-02-06
Implementations for parts of <stdlib.h>. Still missing are the floating
point conversions, and the wide-/multibyte-character functions.

v0.4.1 - 2006-11-16
With v0.5 (<stdio.h>) taking longer than expected, v0.4.1 was set up as
a backport of bugfixes in the current development code.

- #1 realloc( NULL, size ) fails
- #2 stdlib.h - insufficient documentation
- #4  Misspelled name in credits
- #5  malloc() splits off too-small nodes
- #6  qsort() stack overflow
- #7  malloc() bug in list handling
- #8  strncmp() does not terminate at '\0'
- #9  stdint.h dysfunctional
- #10 NULL redefinition warnings

v0.5 - 2010-12-22
Implementations for <inttypes.h>, <errno.h>, most parts of <stdio.h>,
and strerror() from <string.h>.
Still no locale / wide-char support. Enabled all GCC compiler warnings I
could find, and fixed everything that threw a warning. (You see this,
maintainers of Open Source software? No warnings whatsoever. Stop telling
me it cannot be done.) Fixed all known bugs in the v0.4 release.

Near Future
===========
Current development directions are:

Implement portions of the C11 standard that have a direct impact on the way
that PDCLib itself is built. For example, in order to support multithreading,
continues.