HEDALS

HEDALS: highly efficient delay-driven approximate logic synthesis.

HEDALS optimizes the delay of approximate circuits under a given error constraint, such as error rate (ER) constraint, mean error distance (MED) constraint, and mean hamming distance (MHD) constraint. Its diagram is as follows.

Publication

• C. Meng, Z. Zhou, Y. Yao, S. Huang, Y. Chen, W. Qian, “HEDALS: Highly Efficient Delay-driven Approximate Logic Synthesis,” in IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems (TCAD), 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

  • 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

HEDALS relies on three submodules:

• Open-source logic synthesis and verification tool abc
• Open-source logic synthesis tool espresso
• Open-source approximate circuit library EvoApproxLib

There are two ways of downloading HEDALS:

1. Clone the HEDALS project, and then update the submodules:

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

2. Alternatively, clone the HEDALS project as well as the submodules:

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

./hedals.out -i ./input/benchmark/bacs/mult8.blif -l ./input/standard-cell/nangate_45nm_typ.lib --lacType RAC -f 100032 --metrType MED -e 128 -m 0 -o ./tmp

In this example,

• HEDALS inputs the accurate circuit "./input/benchmark/bacs/mult8.blif".
• It uses the standard cell library "./input/standard-cell/nangate_45nm_typ.lib" for technology mapping.
• It uses the "RAC" local approximate change to simplify the circuit.
• It uses 100032 random input patterns to measure the error.
• The error constraint is $MED \le 128$
• It uses mode 0, that is, applying the priority cut-based method proposed in our paper.
• The approximate circuits will be outputted to the folder ./tmp

Configurations

• Use the following command to get help:

./hedals.out -h

The following information will be returned:

usage: ./hedals.out --accCirc=string [options] ... 
options:
  -i, --accCirc        path to accurate circuit (string)
      --appCirc        path to approximate circuit (string [=])
  -l, --standCell      path to standard cell library (string [=input/standard-cell/mcnc.genlib])
  -o, --outpPath       path to approximate circuits (string [=tmp])
      --lacType        lac type: CONST, SASIMI, RAC (string [=CONST])
      --metrType       error metric type: ER, MED, MHD (string [=ER])
      --distrType      error distribution type: UNIF, ENUM (string [=UNIF])
      --mapType        mapping type: SCL, LUT (string [=SCL])
  -s, --sourceSeed     seed for randomness (unsigned int [=0])
  -f, --nFrame         #Monte Carlo samples, nFrame should be an integer multiple of 64 (int [=100032])
  -m, --mode           mode selection, 0 or 1
			0: priority cut
			1: maximum flow (int [=0])
      --usePostProc    whether to use post processing for further reducing the area (int [=0])
      --cutSizeLim     size limit of priority cuts (int [=16])
  -e, --errUppBound    error upper bound (double [=0.15])
  -h, --help           print this message

Long parameter	Short parameter	Default value	Function
--accCirc	-i	None	Path to accurate circuit, e.g., ./input/benchmark/bacs/mult8.blif
--appCirc		""	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 report the 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.
--lacType		CONST	The type of local approximate changes. There are three types: CONST, SASIMI, RAC. CONST means constant replacement. SASIMI means signal replacement. RAC means approximate resubstitution. Please refer to our paper to see more details about the LAC type.
--metrType		ER	The type of error metrics. There are three metrics: ER, MED, MHD. Please refer to our paper to see their detailed definition.
--distrType		UNIF	The type of input distribution. There are two types. UNIF means uniform distribution. ENUM means enumerating all possible input patterns (only for small circuits).
--mapType		SCL	The type of final mapping target. There are two types. SCL means mapping into standard cell library. LUT means mapping into look up tables.
--sourceSeed	-s	0	The seed used for generating random input patterns for logic simulation. When seed "0" is used, then HEDALS randomly picks a seed. Otherwise, HEDALS uses the specified seed.
--nFrame	-f	100032	The number of random input patterns used for error measurement.
--mode	-m	0	Mode selection. There are two modes: 0, 1. Mode 0 corresponds to the priority cut method proposed in our paper. Mode 1 corresponds to the maximum flow method proposed in our paper.
--usePostProc		0	Whether to use post processing for further reducing the area. When it is 0, post processing is disabled. When it is 1, post processing is enabled.
--cutSizeLim		16	Size limit of priority cuts. Its detailed meaning is defined in our paper.
--errUppBound	-e	0.15	Error upper bound used for approximate logic synthesis. HEDALS will generate an approximate circuits satisfying the bound.
--help	-h	None	Print help.