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
gcc -E
to preprocess the source codeInlinec 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