Effortlessly write inline C functions in Python source code

# coding: inlinec
from inlinec import inlinec
@inlinec
def Q_rsqrt(number):
 float Q_rsqrt( float number )
 {
 long i;
 float x2, y;
 const float threehalfs = 1.5F;
 x2 = number * 0.5F;
 y = number;
 i = * ( long * ) &y; // evil floating point bit level hacking
 i = 0x5f3759df - ( i >> 1 ); // what the fuck? 
 y = * ( float * ) &i;
 y = y * ( threehalfs - ( x2 * y * y ) ); // 1st iteration
 return y;
 }
print(Q_rsqrt(1.234))

Inlinec supports gnu-specific c extensions, so you're likely to have reasonable success #includeing glibc headers.

Inspired by Pyxl

Python has a mechanism for creating custom codecs, which given an input token stream, produce an output token stream. Inlinec consumes the entire token stream, runs a fault-tolerant parser on it (parso), finds which function nodes are annotated with an @inlinec decorator, creates a ctypes wrapper for the content of the function, and replaces the function body with a call to the ctypes wrapper. The import for the wrapper is lifted to the top of the file. Once this transformation has been made, the source code is re-tokenized and the Python interpreter only sees the transformed source. So a function like this:

@inlinec
def test():
 #include<stdio.h>
 void test() {
 printf("Hello, world");
 }

Gets turned into:

from test_8281231239129310 import lib as test_8281231239129310_lib, ffii as test_8281231239129310_ffi
@inlinec
def test():
 return test_8281231239129310_lib.test()

In theory, this allows inline c functions to be called with a one-time compilation overhead and the same performance characteristics as ctypes -- the underlying FFI library.

Note: This is just a proof of concept

• Passing pointers to C functions does not currently work (aside from strings)
• Shells out to gcc -E to preprocess the source code
• Compilation is not cached and takes a long time every run
• Compilation pollutes the current directory with .so, .o, .c files
• The source file is parsed multiple times unnecessarily
• Many more

Inlinec requires a C compiler to be installed on the system (tested with GCC and Clang), as well as the python development libraries to be installed (python3-dev). To play around with it in a container you can use the provided Dockerfile, just run docker build, exec into a shell in the container, and you have a working installation of inlinec.

> docker build -t inlinec . && docker run -it inlinec bash