ADAPT: Algorithmic Differentiation for Floating-Point Precision Tuning

This repository contains the source code for the ADAPT tool [1], which allows you to instrument your own C++ code and analyze it with the aim of finding a mixed-precision version (i.e., some double-precision variables have been changed to single precision).

ADAPT performs algorithmic (or "automatic") differentiation [2] and then uses the partial derivatives ("adjoints") to estimate the error introduced by changing each variable's type. It then recommends variables that should be replaced to maximize the amount of conversions under an error threshold that you provide.

[1] Harshitha Menon, Michael O. Lam, Daniel Osei-Kuffuor, Markus Schordan, Scott Lloyd, Kathryn Mohror, and Jeffrey Hittinger. 2018. ADAPT: algorithmic differentiation applied to floating-point precision tuning. In Proceedings of the International Conference for High Performance Computing, Networking, Storage, and Analysis (SC '18). IEEE Press, Piscataway, NJ, USA, Article 48, 13 pages. ACM DL Link

[2] Wikipedia article: "Automatic Differentiation"

Prerequisites

ADAPT depends on CoDiPack [3], a template expression-based library for C++11. This library must be accessible to the compiler, possibly by adding -I/path/to/CoDiPack/folder to CXXFLAGS. You will also need to use the -DCODI_ZeroAdjointReverse=0 preprocessor flag to allow proper access to intermediate adjoints.

You should also consider using -DCODI_EnableImplicitConversion -DCODI_DisableImplicitConversionWarning to enable implicit casts from AD_real to double. This allows you to avoid some AD_value() calls (see Using ADAPT below) but it could also hide unintended conversions (causing a loss of adjoint information).

[3] Max Sagebaum, Tim Albring, and Nicolas R. Gauger. 2017. High-Performance Derivative Computations using CoDiPack. arXiv preprint arXiv:1709.07229. arXiv Link

Getting Started

To build your project with ADAPT, include the ADAPT folder as an include path by adding -I/path/to/ADAPT/folder to CXXFLAGS. Also, you must compile with the -std=c++11 option.

Add the following to each source code file that needs to reference ADAPT:

#include <adapt.h>

Add the following to exactly one source code file (usually the one with your main):

#include <adapt-impl.cpp>

Using ADAPT

Change any variables that you wish to analyze from float or double to AD_real. Tag any independent variables using the AD_INDEPENDENT macro, intermediate results (usually any assignment to the variables of interest) using the AD_INTERMEDIATE macro, and any output variables (and their error threshold) using the AD_DEPENDENT macro. Call AD_begin() before any code that you wish to analyze, and call AD_report() after all of the code that you wish to analyze. Call AD_value() to convert AD_real variables to a double where necessary (e.g., for output).

There are also a couple of options that you can set to change the behavior of the analysis. These options are enabled using function calls:

• AD_enable_absolute_value_error() - Enable taking the absolute value of errors during variable analysis. Useful when the program contains long chains of self-assignments (i.e., reads and writes to the same variable). Must be called before AD_report.

• AD_enable_source_aggregation() - Enable aggregation based on source info of assignments rather than variable definitions. Must be called before any of the AD_INDEPENDENT/AD_INTERMEDIATE macros.

The included demos (in the sanity, sum2pi_x, and arclength folders) provide examples of how to use ADAPT. Consult the README files in those folders for more information about the individual demos.

Getting Involved

To get involved, submit an issue or email the authors directly.

Contributing

To contribute, submit a pull request or email the authors directly.

Release

ADAPT is released under an GPL license. For more details see the NOTICE and LICENSE files.

LLNL-CODE-762758

ADAPT uses the "JSON for Modern C++" library, distributed under the MIT license:

    __ _____ _____ _____
 __|  |   __|     |   | |  JSON for Modern C++
|  |  |__   |  |  | | | |  version 3.1.2
|_____|_____|_____|_|___|  https://github.com/nlohmann/json

Licensed under the MIT License <http://opensource.org/licenses/MIT>.
SPDX-License-Identifier: MIT
Copyright (c) 2013-2018 Niels Lohmann <http://nlohmann.me>.