E-methodHW – Polynomial and Rational Function Approximations for FPGAs

---

---

Project Overview

This project proposes an automatic method for the evaluation of functions via polynomial or rational approximations and their hardware implementations, on FPGAs.

The approximations are evaluated using Ercegovac's iterative E-method ^{1 2} adapted for state-of-the-art and high-throughput FPGA implementations.

The polynomial and rational function coefficients are computed in such a way that they not only satisfy the constraints of the E-method, but are also optimal.

If you would like to find more technical details, as well as comparisons with other tools that offer hardware function approximations, have a look at the research report. You can also have a look at the slides of the presentation that Silviu-Ioan Filip gave at ARITH25, presenting the project.

You can cite this work as:

@inproceedings{FilipIstoanEtAl2018,
  author = {Nicolas Brisebarre, George Constantinides, Miloš Ercegovac, Silviu-Ioan Filip, Matei Istoan, Jean-Michel Muller},
  title = {A High Throughput Polynomial and Rational Function Approximations Evaluator},
  booktitle = {25th IEEE Symposium of Computer Arithmetic (ARITH-25)},
  year = {2018},
  month = Jun,
  nopublisher = {IEEE}
}

If you have any remarks, suggestions or requests, please get in touch.

---

1: M. D. Ercegovac, “A general method for evaluation of functions and computation in a digital computer,” Ph.D. dissertation, Dept. of Computer Science, University of Illinois, Urbana-Champaign, IL, 1975.

2: M. D. Ercegovac, “A general hardware-oriented method for evaluation of functions and computations in a digital computer,” IEEE Trans. Comput., vol. C-26, no. 7, pp. 667–680, 1977.

---

---

Installation Instructions

The E-methodHW project depends on the efrac library and on FloPoCo. In turn, efrac depends on: gmp, mpfr, mpreal, fplll, eigen and qsopt_ex. You can follow instructions on their respective websites in order to install them on your system. FloPoCo has a pretty extensive list of dependencies, that you can check on the project's page. You can also use their one-line install to get everything ready (leave out the download and install of the FloPoCo library, as everything required is provided in this repository). To make things easier (and hoping you have one of the supported distributions), here is the required shell command:

sudo apt-get install g++ libgmp3-dev libmpfr-dev libfplll-dev libxml2-dev bison libmpfi-dev flex cmake libboost-all-dev libgsl0-dev && wget https://gforge.inria.fr/frs/download.php/33151/sollya-4.1.tar.gz && tar xzf sollya-4.1.tar.gz && cd sollya-4.1/ && ./configure && make -j4 && sudo make install

In order to use E-MethodHW you need to start by either cloning (follow the instructions at the top of this page) or downloading and then unpacking the archive. Asuming that the extracted project is in the emethod directory, building the project can be done using the following commands:

cd emethod
cd main
cmake .
make all

Test the program by typing:

./emethodHW --help

There are several build options, that can be passed directly to cmake.

-DCFG_TYPE=Release|Debug

set by default to Release, will generate debug information and show debug messages during compilation if set to Debug.

-DCFG_FLOPOCO=Lib|LibExec

set by default to Lib, allows building FloPoCo as either library only, or library and executable (useful for comparing the performance of E-methodHW, as described in the research report) when set to LibExec.

If you would like to remove the files generated during build or subsequent runs of emethodHW, you can use the clean-all make target by typing:

make clean-all

If you would like to remove the files generated during the build of emethodHW, use the clean-cmake-files:

make clean-cmake-files

If you would like to remove only the files generated during the execution of emethodHW, use the clean-run-files:

make clean-run-files

---

---

Usage

Passing Parameters

There are several ways of passing paremeters to emethodHW. In decreasing order of their priority, they are:

1. command line
2. default values
3. configuration file

Parameters on the command line are passed as:

--<parameter_name>=<value>

The exact format of <value>depends on its actual format (for example, a string is specified between single or double quotes).

Parameters in the configuration file are passed as:

<parameter_name>=value

each on an individual line. You can insert lines that start with # in orderto separate the parameters into groups.

For details on the default values, pull up the help page, by typing:

emethod --help-all

or have a look at the CommandLineParser.cpp file.

If no parameters are provided, emethodHW is configured to run Example 1 from the research report. Not providing some of the required parameters results in the usage of the default one, which might not meet your expectations.

Program Parameters

The following is a list of parameters and their meaning:

Mandatory functional paremeters

• function, f - the function to evaluate; e.g. "((x*4.5)^4 + 1)^0.5"
• weight, w - the weight of the function to evaluate
• delta, d - the value of delta in the E-method algorithm
• radix, r - the radix used for the implementation
• lsbInOut, l - the weight of the least significant bit of the input and the output in the used fixed-point format

Optional functional parameters

• xi, x - the value of xi in the E-method algorithm
• alpha, a - the value of the alpha parameter in the E-method algorithm
• scaleInput - enables/disables the generation of the hardware for scaling the input to the circuit
• inputScalingFactor - value of the input scaling factor
• msbInOut, m - the weight of the most significant bit of the input and the output in the used fixed-point format

Optional perfomance parameters

• verbosity - the verbosity level, controling the amount of messages printed at the command line; ranges from 0=no messages, to 5=all messages
• pipeline - enables/disables the generation of a pipeline for the resulting hardware implementation
• frequency - the target frequency of the resulting hardware implementation (take this with a grain of salt, the generator tries to get a close-enough to the set value); taken into account when pipelining is enabled
• testbench - the number of testcases to be generated; if set to 0, no tests are generated

Miscellaneous options

• version, v - version of emethodHW and of the used libraries
• help, h - produce the help message
• help-all - produce an extended help message
• configFile, c - the name of the file containing the configurations, if it exists

---

---