David Mertens > C-TinyCompiler-0.04 > C::TinyCompiler

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NAME ^

C::TinyCompiler - Full C JIT compiling using the Tiny C Compiler

VERSION ^

Version 0.04

SYNOPSIS ^

Compile C-code in memory at runtime.

 ## A really basic example ##
 
 use strict;
 use warnings;
 use C::TinyCompiler;
 
 # Build a compiler context
 my $context = C::TinyCompiler->new();
 
 # Add some code (but don't compile yet)
 $context->code('Body') = q{
     void say_hi() {
         printf("Hello from C::TinyCompiler!\n");
     }
 };
 
 # Compile our C code
 $context->compile;
 
 # Call our function
 $context->call_void_function('say_hi');
 
 
 ## Make a function that takes arguments ##
 
 # Use the C::TinyCompiler::Callable package/extension
 $context = C::TinyCompiler->new('C::TinyCompiler::Callable');
 
 # Add a function that does something mildly useful
 $context->code('Body') = q{
     C::TinyCompiler::Callable
     double positive_pow (double value, int exponent) {
         double to_return = 1;
         while (exponent --> 0) to_return *= value;
         return to_return;
     }
 };
 
 # Compile our C code
 $context->compile;
 
 # Retrieve a subref to our function
 my $pow_subref = $context->get_callable_subref('positive_pow');
 
 # Exercise the pow subref
 print "3.5 ** 4 is ", $pow_subref->(3.5, 4), "\n";
 
 
 ## Throw exceptions ##
 
 # Use the C::TinyCompiler::Callable and
 # C::TinyCompiler::Perl::Croak packages/extensions
 $context = C::TinyCompiler->new( qw< ::Callable ::Perl::Croak > );
 
 # Add a positive, integer pow() function
 $context->code('Body') = q{
     C::TinyCompiler::Callable
     double positive_pow (double value, int exponent) {
         if (exponent < 0) {
             croak("positive_pow only accepts non-negative exponents");
         }
         double to_return = 1;
         while (exponent --> 0) to_return *= value;
         return to_return;
     }
 };
 
 ## Interface with PDL data ##
 
 $context = C::TinyCompiler->new('::Callable');
 
 # Create a sequence of prime numbers:
 $context->code('Body') = q{
     C::TinyCompiler::Callable
     void prime_sequence (int * output, int length) {
         /* Always start with 2 */
         output[0] = 2;
         
         int n_filled = 1;
         int candidate = 3;
         
         while(n_filled < length) {
             for (int divisor_idx = 0; divisor_idx < n_filled; divisor_idx++) {
                 if (candidate % output[divisor_idx] == 0) goto NEXT_NUMBER;
                 if (output[divisor_idx] * output[divisor_idx] > candidate) break;
             }
             output[n_filled] = candidate;
             n_filled++;
             
             NEXT_NUMBER: candidate++;
         }
     }
 };
 
 # Compile our C code
 $context->compile;
 
 # Retrieve a subref to our function
 my $prime_sequence = $context->get_callable_subref('prime_sequence');
 
 # Allocate some memory for the operation
 use PDL;
 my $primes = zeroes(long, 20);
 
 # Exercise the subref to create the first 20 primes
 $prime_sequence->($primes->get_dataref, $primes->nelem);
 print "First 20 primes are $primes\n";

DESCRIPTION ^

This module provides Perl bindings for the Tiny C Compiler, a small, ultra-fast C compiler that can compile in-memory strings of C code, and produce machine code in memory as well. In other words, it is a full C just-in-time compiler. It works for x86 and ARM processors. The jit-compilation capabilities offered by this module are known to work on Windows, Linux, and Mac OS X.

The goal for this family of modules is to not only provide a useful interface to the compiler itself, but to also provide useful mechanisms for building libraries that utilize this module framework. Eventually I would like to see a large collection of pre-canned data structures and associated algorithms that can be easily assembled together for fast custom C code. I would also like to see C::TinyCompiler modules for interfacing with Perl-based C libraries such as PDL, Prima, and Imager, or major Alien libraries such as SDL, OpenGL, or WxWidgets. But this is only the early stages of development, and the key modules that provide useful functionality are:

C::TinyCompiler::Callable

This module lets you write functions in C that can be invoked from Perl, much like Inline::C.

C::TinyCompiler::StretchyBuffer

This module provides a data structure that handles exactly like a C array but has additional functionality to dynamically change the length, retrieve the current length, and push and pop data at the end.

C::TinyCompiler::Perl::Croak

This module provides an interface to Perl's C-level croak and warn functions, as well as their v-prefixed variants. This way, you can safely throw exceptions from your TinyCompiler-compiled C code.

PRE-COMPILE METHODS ^

The compiler context has three main events that divide the usage into two stages. Those events are creation, compilation, and destruction. Between creation and compilation you can do many things to the compiler context to prepare it for compilation, like adding library paths, setting and unsetting #defines, and adding code. After compilation, you can retrieve symbols (which is how you get at the code or globals that you just compiled) and execute compiled functons

new

Creates a new Tiny C Compiler context. All compiling and linking needs to be run in a context, so before creating any new code, you'll need to create one of these.

Arguments are simply the names of packages that you want applied to your compiler context. For example,

 my $context = C::TinyCompiler->new('::Perl::SV');
 my $context = C::TinyCompiler->new('::Perl::SV', '::Perl::AV');

C::TinyCompiler packages are to C::TinyCompiler what modules are to Perl. They add some sort of functionality to the compiler context, whether that's a set of functions or some fancy source filtering. To learn more about adding packages to your compiler context, see "apply_packages".

add_include_paths, add_sysinclude_paths

Adds include paths or "system" include paths to the compiler context. For example,

 $context->add_include_paths qw(C:\my\win32\headers /my/linux/headers);

Include paths are places to search when you say #include <lib.h> or $include "mylib.h" in your C source. The only difference between a system include path and a regular include path is that all regular include paths are searched before any system include paths. Other important things to know include

Quote-includes check '.' but angle-bracket includes do not

The only difference between saying #include "mylib.h" and #include <mylib.h> is that the first one always looks for mylib.h in the current working directory before checking the include paths, whereas the second one only checks the include paths. By current working directory, I mean the working directory when the "compile" function is invoked.

Adding to the path is like using -I

Adding include paths is similar to the -I command line argument that you get with most (all?) compilers.

First added = first checked

Suppose you have files foo/bar.h and foo/baz/bar.h and you add both foo and foo/baz to your list of include paths. Which header will you get? The compiler will search through the include paths starting with the first path added. In other words, if your file layout looks like this:

 foo/
   bar.h
   baz/
     bar.h

then this series of commands will pull in foo/bar.h rather than foo/baz/bar.h:

 use File::Spec;
 $context->add_include_paths('foo', File::Spec->catfile('foo', 'baz'));
 $context->code('Head') .= {
     #include "bar.h"
 };
The last include path is checked before the first sysinclude path

When your C code has #include "lib.h" or #include <lib.h>, the search process starts off looking in all directories that are in the include path list, followed by all the directories in the system include path list. This is important if you are writing a C::TinyCompiler package. If you want your user to potentially override a header file by adding an include path, you should specify any special include paths with the sysinclude.

Backslashes and qw(), q()

As a notational convenience, notice that you do not need to escape the backslashes for the Windows path when you use qw. That makes Windows paths easier to read, especially when compared to normal single and double quoted strings.

Nonexistent paths are OK

Adding nonexistent paths will not trigger errors nor cause the compiler to croak, so it's ok if you throw in system-dependent paths. It may lead to a minor performance hit when the compiler searches for include files, but that's not likely to be a real performance bottleneck.

Path-separators are OK, but not cross-platform

It is safe to submit two paths in one string by using the system's default path separator. For example, this works on Linux:

 # Linux
 $context->add_include_paths('/home/me/include:/home/me/sources');
 # Windows
 $context->add_include_paths('C:\\me\\include;C:\\me\\sources');

However, the path separator is system-specific, i.e. not cross-platform. Use sparingy if you want cross-platform code.

No known exceptions

There is a line of code in these bindings that check for bad return values, and if triggered it will issue an error that reads thus:

 Unkown tcc error including path [%s]

However, as of the time of writing, C::TinyCompiler will never trigger that error, so I find it highly unlikely that you will ever see it. If you do, these docs and the code need to be updated to query the source of the error and be more descriptive.

Set paths before compiling

This should be obvious, but it's worth pointing out that you must set the include paths before you "compile". If you try to set include paths after compilation, you will not cause any change in the context's state; if you have warnings enabled, you will get a message like:

 Adding include paths after the compilation phase has no effect.

or

 Adding sysinclude paths after the compilation phase has no effect.

add_library_paths

Adds library paths, similar to using -L for most compilers. For example,

 $context->add_library_paths('C:\\mylibs', '/usr/home/david/libs');

would be equivalent to saying, on the command line:

 cc ... -LC:\\mylibs -L/usr/home/david/libs ...

Notice that the paths are not checked for existence before they are added. Also, adding library paths after the compilation phase has no effect and, if you have warnings enabled, will issue this statement:

 Adding library paths after the compilation phase has no effect.

add_librarys

Adds the libraries, similar to using -l for most compilers. For example,

 $context->add_librarys('gsl', 'cairo');

would be equivalent to saying, on the command line:

 cc ... -llibgsl -llibcairo ...

You must perform all additions before the compilation phase.

If the compiler cannot find one of the requested libraries, it will croak saying

 Unable to add library %s

define

This defines a preprocessor symbol (not to be confused with "add_symbols", which adds a symbol to the compiler lookup table). It takes the preprocessor symbol name and an optional string to which it should be expanded. This functions much like the -D switch for most (all?) compilers. In this way, having this in your Perl code

 $context->define('DEBUG_PRINT_INT(val)'
     , 'printf("For " #val ", got %d\n", val)');

gives similar results as having this at the top of your C code:

 #define DEBUG_PRINT_INT(val) printf("For " #val ", got %d\n", val)

In fact, tcc (and thus C::TinyCompiler) even supports variadic macros, both directly in C code and using this method.

Normally in C code, you might have such a definition within a #ifdef block like this:

 #ifdef DEBUG
 #    define DEBUG_PRINT_INT(val) printf("For " #val ", got %d\n", val)
 #else
 #    define DEBUG_PRINT_INT(val)
 #endif

Since you control what gets defined with your Perl code, this can be changed to something like this:

 if ($context->{is_debugging}) {
     $context->define('DEBUG_PRINT_INT(val)'
         , 'printf("For " #val ", got %d\n", val)');
 }
 else {
     $context->define('DEBUG_PRINT_INT(val)');
 }

Another nicety of Perl-side macros is that they can be defined as multi-line more cleanly. For example, this C macro

 #define DEBUG_PRINT_INT(val) \
     do { \
         printf("For " #val ", got %d\n", val); \
     } while (0)

can be notated with a Perl-side define simply as

 $context->define ('DEBUG_PRINT_INT(val)' => q{
     do {
         printf("For " #val ", got %d\n", val);
     } while (0)
 });

There are differences between how Perl-side and C-side macro definitions operate, but arguably the most important is that the second form lets you query the definition from Perl. The overhead involved for such queries likely makes #define statements in C code are marginally faster than Perl-side defines, but I have a hard time believing that is a real bottleneck in your code. I suggest you optimize this for developer time, not execution time.

If you do not provide a symbol, an empty string will be used instead. This varies slightly form the libtcc usage, in which case if you provide a null pointer, the string "1" is used. Thus, if you want a value of "1", you will need to explicitly do that.

If you attempt to modify a preprocessor symbol that has already been defined, the behavior will depend on whether or not you have enabled C::TinyCompiler warnings. These warnings are enabled if you say use warnings in your code, so if you are like most people, these are probably on by default. If you want to suppress redefinition warnings for a small chunk of code, you should say something like this:

 ...
 {
     no warnings 'C::TinyCompiler';
     $context->define('symbol', 'new_value');
 }
 ...

Also, this function will croak if you attempt to modify a preprocessor symbol after you have compiled your code, saying:

 Error defining [$symbol_name]:
   Cannot modify a preprocessor symbol
   after the compilation phase

If you want to check if the context has compiled, see "has_compiled".

is_defined

Returns a boolean value indicating whether or not the given preprocessor symbol has been defined using the "define" method. You can call this method both before and after compiling your code, but this is not aware of any #define statements in your C code.

For example:

 $context->define('DEBUGGING', 2);
 
 # ...
 
 if ($context->is_defined('DEBUGGING')) {
     # More debugging code here.
 }

definition_for

If you defined the given preprocessor macro using the "define" method, this returns the (unexpanded) preprocessor definition that you supplied. If the macro was not defined using "define" (or has subsequently been "undefine"d), this function will return Perl's undef.

For example:

 $context->define('DEBUGGING', 2);
 
 # ...
 
 if ($context->definition_for('DEBUGGING') > 2) {
     # Debugging code for highly debuggish setting
 }

Bear in mind a number of important aspects of how this works. First, if the value is not defined, you will get an undefined value back; using this in a mathematical expression or trying to convert it to a string will make Perl grumble if you use warnings. Second, the values of 0 or the blank string (blank strings are the default values if no value is supplied when you call "define") are valid values even though these are false in boolean context. Thus, if you simply want to know if a preprocessor symbol is defined, you should use "is_defined" instead. That is to say:

 # BAD UNLESS YOU REALLY MEAN IT
 if ($context->definition_for('DEBUGGING')) {
     # ...
 }
 
 # PROBABLY WHAT YOU MEANT TO SAY
 if ($context->is_defined('DEBUGGING')) {
     # ...
 }

undefine

Undefines the given preprocessor symbol name. Remember that this happens before any of the code has been compiled; you cannot call this dynamically in the middle of the compilation process.

This should not throw any errors. In particular, it should not gripe at you if the symbol was not defined to begin with. However, it is still possible for something deep inside tcc to throw an error, in which case you will get an error message like this:

 Error undefining preprocessor symbol [%s]: %s

But I don't expect that to happen much.

code

XXX THIS INTERFACE IS LIKELY TO CHANGE IN THE NEAR FUTURE XXX

This lvalue sub lets you get, set, append to, and otherwise modify the contents of the code in each of three regions. Any value is allowed so long as the compile-phase can retrieve a useful string. This means that you can even set the different code sections to be objects.

The location is the first argument and is a string, so the convention might look something like this:

 $context->code('Head') = q{
     double my_dsum(double, double);
 };

though I generally recommend that you append to each section rather than overwriting. To append to the Body section, for example, you would say:

 $context->code('Body') .= q{
     double my_dsum(double a, double b) {
         return a+b;
     }
 };

You can even hammer on these sections with a regular expression:

 $context->code('Head') =~ s/foo/bar/g;

Valid locations include:

Head

Should come before any function definitions. Appropriate for function and global variable declarations.

Body

Should contain function definitions.

Foot

Should come after function definitions. I'm not actually sure what should go here, but I thought it might come in handy. :-)

You can use whichever form of capitalization you like for the sections, so head, Head, and HEAD are all valid.

If you have a compiler error, line numbers will be meaningless if you do not tell the compiler the line on which the code is run. To do this properly, use "line_number", discussed below.

working here - note that warnings are not issued for changing code values after the compilation phase, but such changes can have no effect.

line_number

Build a line number directive for you. Use like so:

 $context->code('Body') .= C::TinyCompiler::line_number(__LINE__) . q{
     void test_func (void) {
         printf("Success!\n");
     }
 };

Suppose you have an error in your code and did not use this (or some other means) for indicating your line numbers. The offending code could be

 $context->code('Body') .= q{
     void test_func (void {
         printf("Success!\n");
     }
 };

which, you will notice, forgets to close the parenthesis in the function definition. This will raise an error that would look like this:

 Unable to compile at Body line 2: parameter declared as void

Although it tells you the section in which the error occurred, if you have a complex script that adds code in many places, you may have no idea where to find offending addition in your Perl code. Fortunately, C (and Perl) allows you to give hints to the compiler using a #line directive, which is made even easier with this function. Without line_number, you would say something like:

 $context->code('Body') .= "\n#line " . (__LINE__+1) . ' "' . __FILE__ . q{"
     ... code goes here ...
 };

and then your error reporting would say where the error occurred with respect to the line in your script. That formula is long-winded and error prone, so you can use this useful bit of shorthand instead:

 $context->code('Body') .= C::TinyCompiler::line_number(__LINE__) . q{
     ... code goes here ...
 };

Still not awesome, but at least a little better.

apply_packages

Adds the given packages to this compiler context. The names should be the name of the Perl package that has the functions expected by the C::TinyCompiler package mechanisms:

 $context->apply_packages qw(C::TinyCompiler::Perl::SV C::TinyCompiler::Perl::AV);

The C::TinyCompiler is optional, so this is equivalent to:

 $context->apply_packages qw(::Perl::SV ::Perl::AV);

Options are package-specific strings and should be specified after the package name and enclosed by parentheses:

 $context->apply_packages qw(::Perl::SV(most) ::Perl::AV(basic))

You can call this function multiple times with different package names. However, a package will only be applied once, even if you specify different package options. Thus, the following will not work:

 $context->apply_packages '::Perl::SV(basic)';
 $context->apply_packages '::Perl::SV(refs)';

Instead, you should combine these options like so:

 $context->apply_packages '::Perl::SV(basic, refs)';

Note that you can put spaces between the package name, the parentheses, and the comma-delimited options, but qw() will not do what you mean in that case. In other words, this could trip you up:

 $context->apply_packages qw( ::Perl::SV(basic, refs) );

and it will issue a warning resembling this:

 Error: right parenthesis expected in package specification '::Perl::SV(basic,'

Again, these are OK:

 $context->apply_packages qw( ::Perl::SV(basic) );
 $context->apply_packages '::Perl::SV (basic)';

but this is an error:

 $context->apply_packages qw( ::Perl::SV (basic) );

and will complain saying:

 Error: package specification cannot start with parenthesis: '(basic)'
     Is this supposed to be an option for the previous package?

For more discussion on packages, see "MANAGING PACKAGES".

MANAGING PACKAGES ^

Certain packages require other packages, and some packages do not play nicely together. The current package management system is not very sophisticated, but it does provide a means for packages to indicate dependencies and conflicts with others. In general, all of this should be handled by the packages and manual intervention from a user should usually not be required.

As far as the compiler is concerned, a package can be in one of three states: (1) applied, (2) blocked, or (3) unknown. An applied package is any package that you have applied directly or which has been pulled in as a package dependency (but which has not been blocked). A blocked package is one that should should not be applied. An unknown package is one that simply has not been applied or blocked.

As an illustration of this idea, consider the C::TinyCompiler::Perl package and the light-weight sub-packages like C::TinyCompiler::Perl::Croak. The light-weight packages provide a exact subset of C::TinyCompiler::Perl, so if C::TinyCompiler::Perl is loaded, the sub-packages need to ensure that they do not apply themselves or, if they have already been applied, that they remove themselves. This check and manipulation occurs during the sub-packages' call to conflicts_with

is_package_applied, is_package_blocked, is_package_known

Three simple methods to inquire about the status of a package. These return boolean values indicating whether the package (1) is currently being applied, (2) is currently blocked, or (3) is either being applied or blocked.

block_package

Blocks the given package and removes its args from the applied package list if it was previously applied.

get_package_args

Returns the array ref containing the package arguments that were supplied when the package was applied (or an empty array ref if the package was never applied or has subsequently been blocked). This is the actual array reference, so any manipulations to this array reference will effect the reference returned in future calls to get_package_args.

COMPILE METHODS ^

These are methods related to compiling your source code. Apart from compile, you need not worry about these methods unless you are trying to create a C::TinyCompiler package.

compile

Concatenates the text of the three code sections, jit-compiles them, applies all symbols from the included packages, and relocates the code so that symbols can be retrieved. In short, this is the transformative step that converts your code from ascii into machine.

This step does far more than simply invoke libtcc's compile function. At the time of writing, tcc only supports a single uncompiled compiler state at a time. To properly handle this, C::TinyCompiler defers creating the actuall TCCState object as long as possible. Calling the compile method on your compiler context actually performs these steps:

1. Create TCCState

An actual TCCState struct is created, to which the following operations are applied.

2. Apply preprocessor definitions, paths, libraries

All preprocessor defintions, include paths, library paths, and libraries are added to the compiler state.

3. Invoke preprocessing methods of all C::TinyCompiler packages

Packages can perform preprocessing on the compiler context (and in particular, the code strings) just before the actual compilation step. This allows them to dynmically add or remove elements to your code, like source-filters. Or they could hold off to perform other changes to the compiler context until just before the compilation step, although this is generally not needed.

4. Code assembly and compilation

The code is assembled and compiled.

5. Apply symbols and relocate the machine code

Symbols (such as dynamically loaded functions) are applied, the final machine code is relocated, and the memory pages holding that code are marked as executable.

This means that nearly all of the interaction with libtcc itself is deferred until you call this function. As each of those interactions could encounter trouble, this function may croak for many reasons.

This context has already been compiled

You are only allowed to compile a context once.

Error defining processor symbol <name>: <message>

tcc encountered trouble while trying to define the given preprocessor symbol. Duplicate preprocessor symbols should not occurr at this stage, so this error likely means that your definition is malformed.

Error adding include path(s): <message> =item Error adding library path(s): <message>

An include path, sysinclude path, or library path gave trouble. The tcc source code has no code path that should issue this error, so this should never happen. If it does, either you really messed something up, or there's a bug in this module. :-)

Error adding library(s): <message>

tcc encountered trouble adding one or more of your specified libraries. Hopefully the message explains the trouble well enough.

Unable to compile ...

If your code has a syntax error or some other issue, you will get this message. If the reported line numbers do not help, consider using "line_numbers" to improve line number reporting.

Error adding symbol(s): <message>

If you specify symbols that have already been defined elsewhere, the compiler will thwart your attempts with this message. Make sure that you have not defined a like-named symbol already. In particular, be sure not to define a symbol that was defined already by one of your packages.

Unable to relocate: <message>

The last step in converting your C code to machine-executable code is relocating the bytecode. This could fail, though I do not understand compilers well enough to explain why. If I had to guess, I would say you probably ran out of memory. (Sorry I cannot provide more insight into how to fix this sort of problem. Feedback for a better explanation would be much appreciated. :-)

add_symbols

Adds symbols to a compiler context. This function expects the symbols as

 symbol_name => pointer

pairs. By symbol, I mean any C thing that you want to give a name in your compiler context. That is, you can add a function to your compiler context that was compiled elsewhere, or tell the compiler context the location of some variable that you wish it to access as a global variable.

This function requires that you send a true C pointer that points to your symbol. This only makes sense if you have a way to get C pointers to your symbols. This would be the case if you have compiled code with a separate C::TinyCompiler context (in which case you would use "get_symbols" to retrieve that pointer), or if you have XS code that can retrieve a pointer to a function or global variable for you.

working here - add examples, and make sure we can have two compiler contexts at the same time.

For example, the input should look like this:

 $context->add_symbols( func1 => $f_pointer, max_N => $N_pointer);

If you fail to provide key/value pairs, this function will croak saying

 You must supply key => value pairs to add_symbols

POST-COMPILE METHODS ^

These are methods you can call on your context after you have compiled the associated code.

get_symbols

Retrieves the pointers to a given list of symbols and returns a key/value list of pairs as

 symbol_name => pointer

get_symbol

Like "get_symbols", but only expects a single symbol name and only returns the pointer (rather than the symbol name/pointer pair). For example,

 $context->code('Body') .= q{
     void my_func() {
         printf("Hello!\n");
     }
 };
 $context->compile;
 my $func_pointer = $context->get_symbol('my_func');

call_void_function

Takes the name of a compiled function and calls it without passing any arguments. In other words, this assumes that your function has the following definition:

 void my_func (void) {
     ...
 }

This is pretty dumb because it is nearly impossible to pass parameters into the function, but is useful for testing purposes. Note that if you try to call it before you have compiled, you will get this message:

 Cannot call a function before the context has compiled.

is_compiling

An introspection method to check if the context is currently in the compile phase. This is particularly useful for packages whose behavior may depend on whether they are operating pre-compile, post-compile, or during compile.

has_compiled

An introspection method to check if the context has compiled it code or not. You are still allowed to modify the content of your code sections after compilation, but you will not be able to recompile it.

Writing Functions ^

Working here. Sorry. :-)

TODO ^

Add docs for report_if_error and get_error_message

Research and add set_linker if it seems appropriate.

AUTHOR ^

David Mertens, <dcmertens.perl at gmail.com>

BUGS ^

Please report any bugs or feature requests at the project's main github page: http://github.com/run4flat/perl-TCC/issues.

SUPPORT ^

You can find documentation for this module with the perldoc command.

    perldoc C::TinyCompiler

You can also look for information at:

ACKNOWLEDGEMENTS ^

The tcc developers who have continued refining and improving the wonderlul little compiler that serves as the basis for this project!

LICENSE AND COPYRIGHT ^

Portions of this code are copyright 2011-2013 Northwestern University. Portions of this code are copyright 2013 Dickinson College. Documentation copyright 2011-2013 David Mertens.

This program is free software; you can redistribute it and/or modify it under the terms of either: the GNU General Public License as published by the Free Software Foundation; or the Artistic License.

See http://dev.perl.org/licenses/ for more information.

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