Fasten

Fasten is a tool for finding more optimal static configurations of programs. It takes a directory tree of annotated source code, generates a population of variants of that tree, and evolves those variants over several generations to find a configuration that is more optimal according to a given fitness function.

Example

Annotating Source

Integers followed by /* TYPE FASTENABLE */ are enabled for optimization, where TYPE is one of:

• BOOL: a boolean (0 or 1) to toggle
• INT: an integer to increment or decrement
• POW: a power of two to double or halve

#define BUFFER_SIZE 128 /* POW FASTENABLE */

Testing Fitness

The fitness function should produce a single floating-point value, such as a total time. A lower value is considered better.

#!/bin/bash
time -p ( bin/project --benchmark > output 2> errors ) 2>timing
perl -ne 'if (/real\s+([\d.]+)/) { printf "%f", $1; }' timing

Running Fasten

Fasten takes a regex of file paths to load, a command for resetting the tree, a build command, the fitness function, and the directories to search for sources. Note that your file regex does not need to match all files in your project, only those that you want to be searched for FASTENABLE directives.

fasten \
  --files "(\\.c|\\.h)$"
  --reset "git checkout ." \
  --build "make" \
  --fitness "fitness.sh" \
  /path/to/project

See --help for full usage.

Interpreting Output

Fasten produces an array of fittest individuals, in descending order of fitness. An individual is an array of changes made to the tree, such as:

path/to/file.c:100: change 512 to 1024.

You may achieve even better performance by judiciously combining the top few individuals.