David Mertens

There are many things you might do to speed up your Perl code. After profiling and benchmarking, you revise the slow spots, or maybe try a different algorithm. If you still need more speed, you may use Inline::C, or use PDL if you are doing numerics, or even write your own XS code. Reini Urban has even tried to create a Perl Backend that rewrites your Perl code as C code, and has even worked on a port of Perl5 to Potion.

But let's face it. Sometimes it would just be easier if you could write your code in C, and interpolate a string into it. Wouldn't it be nice if there was a C equivalent of Perl's string eval?

Well, in Perl, now there is.

First, some background. The Tiny C Compiler is a small, fast, nearly C99 compliant C compiler written for Linux and Windows, which can also compile object code on Mac (but cannot produce Mach-O executables or dylibs). It targets 32- and 64-bit Intel instruction sets as well as ARM architectures. The compiler is very fast, but what you get in compile-time speed you lose in non-optimized machine code. However, it's still machine code, and it offers a library that includes functionality for compiling arbitrary strings of C code at runtime!

C::TinyCompiler provides an interface to using that just-in-time compilation capability, as well as a framework for building reusable components in the system. This provides the string eval for C code. :-)

The reason I am writing about this today is because I just pushed the firs version of Alien::TinyCC to CPAN. Alien::TinyCC installs the Tiny C Compiler to a non-invasive location which is almost certainly not in the user's path, but the module itself fiddles with $ENV{PATH} and, possibly, $ENV{LD_LIBRARY_PATH} to ensure that the compiler and its main library are available within the Perl environment that invokes the module. Note that this module does not pay any attention to a local install of tinycc, it always installs tcc under the distribution sharedir for Alien::TinyCC.

What does this mean? If you are using one of the major platforms (Window, Mac, Linux) and have to generate code at runtime, try

cpanm C::TinyCompiler

It should Just Install (at least, once Alien::TinyCC 0.02 reaches your local cpan mirror). Then check out C::TinyCompiler::Callable so you can learn how to invoke your C functions from your Perl code, C::TinyCompiler::Perl::Croak so you can throw Perl exceptions in your C code, and C::TinyCompiler::StretchyBuffer so you can push and pop on C arrays as if they were Perl arrays.

The library is still in the early stages of development, and I'd love feedback and ideas. I'm sure the Alien package breaks a few rules here and there (on Unixen it directly installs tcc into the sharedir, for example, which probably breaks some indexing system somewhere) and the code underlying C::TinyCompiler::Callable could be substantially streamlined, I'm sure. But I figured it was important to get the thing out ther and let folks play with it.

Let me close with this simple example interfacing PDL data with a function written using C::TinyCompiler:

 use strict;
 use warnings;
 use PDL;
 use C::TinyCompiler;
 my $context = C::TinyCompiler->new('::Callable');
  
 # Write a function to 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";