MECALS

MECALS: maximum error checking technique for approximate logic synthesis.

This tool synthesizes approximate circuits under the maximum error constraint, such as worst-case error (WCE) and maximum square error (MaxSE) constraint. Its diagram is as follows.

Publication

C. Meng, J. Sun, Y. Mai, W. Qian, “MECALS: a maximum error checking technique for approximate logic synthesis,” in ACM/IEEE Design, Automation & Test in Europe Conference & Exhibition (DATE), Antwerp, Belgium, 2023.

Dependencies

Reference environment, Ubuntu 20.04 LTS with the following tools and libraries:
- gcc 10.3.0 & g++ 10.3.0
  
  You can install these tools with the following command:
```
sudo apt install gcc-10
sudo apt install g++-10
```
  You also need to check whether the default versions of gcc and g++ are 10.3.0:
```
gcc --version
g++ --version
```
  If the default versions of gcc and g++ are not 10.3.0, please change them to 10.3.0.
- cmake 3.16.3
  
  You can install the tool using the following command:
```
sudo apt install cmake
```
- yosys
  
  You can install the tool using the following command:
```
sudo apt install yosys
```
- abc
  
  You need to manually compile abc and add the path where the executable program abc locates to the environment variable.
- libboost 1.75.0
  
  You can download libboost 1.75.0, manually compile it, and then install it.
- libreadline 8.0-4
  
  You can install the library using the following command
```
sudo apt install libreadline-dev
```
Alternatively, we package a docker image containing the above dependencies:

https://hub.docker.com/r/changmeng/als_min

How to Download

This project relies on two submodules:

Open-source logic synthesis and verification tool abc
Open-source logic synthesis tool espresso

There are two ways of downloading this project:

Clone the project, and then update the submodules:

git clone https://github.com/SJTU-ECTL/MECALS.git
git submodule init
git submodule update

Alternatively, clone the project as well as the submodules:

git clone --recursive https://github.com/SJTU-ECTL/MECALS.git

How to Build

To build, go to the root directory of the project, and then execute:

mkdir build
cd build
cmake ..
make
cd ..

An executable program called als.out will be generated at the project root directory.

To clean up, go to the root directory of the project, and then execute:

rm -r build

How to Run

Example command:

./als.out -i input/benchmark/aig/mac.aig -m input/miter/width_8_wce_31.aig -l ./input/standard-cell/nangate_45nm_typ.lib -o tmp/ -p 1.0 --fSASIMI 1

In this example,

The tool inputs the accurate circuit "input/benchmark/aig/mac.aig"
The error constraint is specified by the error miter "input/miter/width_8_wce_31.aig". A general error miter is shown below.

In the file "input/miter/width_8_wce_31.aig", both the outputs of exact and approximate circuits, $\mathbf y$ and $\mathbf {\hat y}$, have a bit width of 8. The WCE bound $B=31$, which means WCE should not exceed 31.
It uses the standard cell library "./input/standard-cell/nangate_45nm_typ.lib" for technology mapping.
The approximate circuits will be outputted to the folder ./tmp

Configurations

Use the following command to get help:

./als.out -h

The following information will be returned:

usage: ./als.out --accCirc=string --mitCirc=string [options] ... 
options:
  -i, --accCirc         path to accurate circuit (string)
  -m, --mitCirc         path to miter circuit (string)
  -a, --appCirc         path to approximate circuit; if this option is not empty, then error checking is performed (string [=])
  -l, --standCell       path to standard cell library (string [=input/standard-cell/nangate_45nm_typ.lib])
  -o, --outpPath        path to approximate circuits (string [=tmp/])
  -s, --seed            seed (unsigned int [=0])
  -f, --nFrame          #simulation patterns (int [=8192])
      --fSASIMI         flag of using SASIMI (int [=1])
  -p, --exactPBDPerc    proportion of exact PBD (double [=1])
  -h, --help            print this message

Long parameter	Short parameter	Default value	Function
--accCirc	-i	None	Path to accurate circuit, e.g., input/benchmark/aig/mac.aig
--mitCirc	-m	None	Path to error miter circuit, e.g., input/miter/width_8_wce_31.aig. You can find more error miters in the folder input/miter/. To specify an arbitrary miter, you can refer to the functions GenWCEMit and GenMaxSEMit in the Python code script/run.py
--appCirc	-a	""	Path to approximate circuit. When "--appCirc" specifies a non-empty string, then the program will iteratively simplify the accurate circuit provided by "--accCirc". Otherwise, if "--appCirc" specifies an empty string "", then the program will check the maximum error of the approximate circuit provided by "--appCirc", compared to the accurate circuit provided by "--accCirc".
--standCell	-l	input/standard-cell/mcnc.genlib	Path to standard cell library, e.g., ./input/standard-cell/nangate_45nm_typ.lib
--outpPath	-o	tmp	Specify the directory where the approximate circuits are outputed.
--seed	-s	0	The seed used for generating random input patterns for logic simulation. When seed "0" is used, then the program randomly picks a seed. Otherwise, the program uses the specified seed.
--nFrame	-f	8192	The number of random input patterns in logic simulation. In our work, simulation is used for quickly filtering some invalid local approximate changes (LACs).
--fSASIMI		1	Whether to use SASIMI LAC or not. If "--fSASIMI" is set to 1, then both SASIMI and CONST LACs will be applied. Otherwise, if "--fSASIMI" is set to 0, then only the CONST LAC will be applied. Please refer to our paper to see the definitions of LACs.
--exactPBDPerc	-p	1	The proportion of nodes using exact partial Boolean difference. This value is a float-point number, ranging from 0.0 to 1.0. Its detailed definition is introduced in our paper.
--help	-h	None	Print help.