Limbo
Limbo Library for VLSI CAD Design

All components are written with C/C++ and API is designed for easy usage and simple embedding. Please read this Readme file carefully for proper instructions to install and customize.

See documentation.

# Packages

Packages Languages Description
Algorithms C++ Useful algorithms including partitioning, coloring, etc.
Bibtex Python Scripts convert bibtex into various formats
Containers C++ Extension of contains from STL
Geometry C++ Geometric utilities and algorithms such as polygon-to-rectangle conversion
MakeUtils Makefile Makefile utilities that help find dependencies
Math C++ Extension of math functions from STL
Parsers C++, Flex/Bison Parsers to various formats, such as LEF/DEF, verilog, GDSII, etc.
Preprocessor C++ Macros such as assertion with message
ProgramOptions C++ Easy API to parser command line options
Solvers C++ Solver wrap-ups such as SDP, LP solver with min-cost flow, etc.
String C++ Utilities to char and string
ThirdParty C/C++, Fortran Third party packages required

# Introduction

## 1. Flex

• A fast scanner generator or lexical analyzer generator. Another famous related software is Lex.

## 2. Bison

• A Yacc-compatible parser generator that is part of the GNU Project. For details, please refer to here. Another famous related software is Yacc.

## 3. (Deprecated) Boost.Spirit

• An object-oriented, recursive-descent parser and output generation library for C++. For details, please refer to here.

## 4. LL Parser

• In computer science, a LL parser is a top-down parser for a subset of context-free languages. It parses the input from Left to right, performing Leftmost derivation of the sentence.

## 5. LR Parser

• In computer science, LR parsers are a type of bottom-up parsers that efficiently handle deterministic context-free languages in guaranteed linear time.

## 6. LL v.s. LR

• Bison is based on LR parser and Boost.Spirit is based on LL parser. Please refer to here.

## 7. LP and Min-Cost Flow

• Min-cost flow (MCF) is a special case of linear programs (LP). It is usually faster than general LP solver and is also able to achieve integer solution. Some LP can be directly transformed to MCF problem, and for some other LP, its duality is a MCF problem. In this library, an API for lemon (MFC solver) is implemented to solve LP and dual LP problems. The API supports reading files with both LGF (lemon graph format) and LP (linear program format) and then dump out solutions. Thus, it will be easier to verify results with general LP solvers such as Gurobi or CBC.

# Bug Report

Please report bugs to yibolin at utexas dot edu.

# Installation

Some components depend on external libraries, such as

• Boost: require BOOST_DIR environment variable to the path where Boost is installed. Limbo library is tested through Boost 1.55.0 to 1.57.0.
• Lemon: require LEMON_DIR environment variable to the path where Lemon is installed.
• Gurobi: require GUROBI_HOME environment variable to the path where Gurobi is installed.
• Flex: require FLEX_DIR or LEX_INCLUDE_DIR environment variable if the flex version is not 2.5.37. See FAQ for details.
• Zlib (optional): require ZLIB_DIR environment variable to enable zlib features. If both zlib and boost are available, Gds parser supports reading/writing .gds.gz files.

Users need to make sure they are properly installed and the corresponding settings are configured.

## 1. Default installation

• In the directory of limbo library, run
make
make doc (optional)                       # generate documentation
make test (optional)                      # build test programs
make install PREFIX=an_absolute_path


The default installation path is the same as building path. Please do not set PREFIX with a relative path. After installation, it is strongly recommended to export LIMBO_DIR to the path where Limbo library is installed as an environment variable.

## 2. Customize CXX, CC and FC options

• CXX sets the compiler for C++ and CC sets the compiler for C. FC sets the fortran compiler which is only needed by some third party packages like OpenBLAS. Some examples are as follows,
make CXX=g++ CC=gcc FC=gfortran (default for Linux)
make CXX=clang++ CC=clang FC=gfortran (default for Mac/Darwin)


## 3. Customize CXXSTDLIB and CXXSTD options

• CXXSTDLIB is used to control -stdlib=xxx under clang++, and CXXSTD is used to control -std=xxx in most compilers.

Under clang, following combinations are valid,

make CXXSTDLIB="-stdlib=libstdc++" CXXSTD="-std=c++98" (default)
make CXXSTDLIB="-stdlib=libc++" CXXSTD="-std=c++98"
make CXXSTDLIB="-stdlib=libc++" CXXSTD="-std=c++11"


Under gcc, there is no -stdlib option, so following combinations are valid,

make CXXSTD="-std=c++98" (default)
make CXXSTD="-std=c++11"


Users must make sure the setting is consistent to dependent libraries during compilation, such as Boost, Lemon, etc. For example, if Boost is compiled with "clang++ -stdlib=libstdc++ -std=c++98", the same setting should be used for components dependent to Boost.

## 4. Customize OPENBLAS options

• There is a third party OpenBLAS required by some other third party packages, such as Csdp. OPENBLAS option is used to control whether compiling these packages.

If you do not need these packages, set OPENBLAS=0 (default); otherwise, set OPENBLAS=1. The default version of OpenBLAS is not very stable for cross platforms, which often results in compiling errors. OpenBLAS is integrated as a submodule which fetch source code from remote repository, so it is always up-to-date version. If you already have OpenBLAS in the directory, simply run "git submodule update" to fetch the latest version in the submodule directory.

# FAQ

## 1. (Deprecated) Compiling errors like

LefScanner.cc:5582:21: error: out-of-line definition of 'LexerInput' does not match any declaration in 'LefParserFlexLexer'
size_t yyFlexLexer::LexerInput( char* buf, size_t max_size )


come from old versions of flex, such as 2.5.35.

A: It can be solved by installing correct flex version 2.5.37 and add the directory to correct flex to PATH environment variable.

## 2. (Deprecated) Compiling errors like

LefScanner.cc:3195:8: error: member reference type 'std::istream *' (aka 'basic_istream<char> *') is a pointer; did you mean to use '->'?
yyin.rdbuf(std::cin.rdbuf());


come from new versions of flex, such as 2.6.0.

A: It can be solved by installing correct flex version 2.5.37 and add the directory to correct flex to PATH environment variable.

## 3. Compiling errors related to LefScanner.cc usually come from the configurations of flex version and environment variables FLEX_DIR and LEX_INCLUDE_DIR.

A: LefScanner.cc needs to include the correct FlexLexer.h from the flex package for compilation; i.e., the version of FlexLexer.h must match the version of the flex executable. Most errors for LefScanner.cc are caused by the failure of finding the correct FlexLexer.h (be careful when you have multiple versions of flex installed). To solve the problem, users can set the environment variable FLEX_DIR such that \$FLEX_DIR/include points to the directory containing FlexLexer.h, or alternatively set LEX_INCLUDE_DIR to the directory containing FlexLexer.h. The decision can be made according to how the flex package is installed.

## 4. Crappy linkage error under gcc 5.1 or later, even though libxxx.a is correctly linked, like

undefined reference to GdsParser::read(GdsParser::GdsDataBaseKernel&, std::string const&)'
`

A: The issue probably comes from potential inconsistent compiling configuration for Limbo and target program due to the new Dual ABI introduced since gcc 5.1. The compilation flag _GLIBCXX_USE_CXX11_ABI is used to control whether gcc uses new C++11 ABI, which is turned on in default. If Limbo is compiled with C++11 ABI, while target program is compiled with old ABI, then the linkage error appears, vice versa. Therefore, it is necessary to make sure the same STL ABI is used for compiling Limbo and target program. In other words, set consistent _GLIBCXX_USE_CXX11_ABI values. A safe way is to leave it to the default value.

The software is released under MIT license except third party packages. Please see the LICENSE file for details.

Third party package csdp is released under CPL v1.0 license.