Auxiliary libraries

The Yosys source distribution contains some auxiliary libraries that are compiled into Yosys and can be used in plugins.


The files in libs/bigint/ provide a library for performing arithmetic with arbitrary length integers. It is written by Matt McCutchen.

The BigInt library is used for evaluating constant expressions, e.g. using the ConstEval class provided in kernel/consteval.h.

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The dlfcn library enables runtime loading of plugins without requiring recompilation of Yosys. The files in libs/dlfcn-win32 provide an implementation of dlfcn for Windows.

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The files in libs/ezsat provide a library for simplifying generating CNF formulas for SAT solvers. It also contains bindings of MiniSAT. The ezSAT library is written by C. Wolf. It is used by the sat pass (see sat - solve a SAT problem in the circuit).


libfst files from gtkwave are included in libs/fst to support reading/writing signal traces from/to the GTKWave developed FST format. This is primarily used in the sim command.


For reading/writing designs from/to JSON, read_json and write_json should be used. For everything else there is the json11 library:

json11 is a tiny JSON library for C++11, providing JSON parsing and serialization.

This library is used for outputting machine-readable statistics (stat with -json flag), using the RPC frontend (connect_rpc), and the yosys-witness yw format.


The files in libs/minisat provide a high-performance SAT solver, used by the sat command.


The files in libs/sha1/ provide a public domain SHA1 implementation written by Steve Reid, Bruce Guenter, and Volker Grabsch. It is used for generating unique names when specializing parameterized modules.


The files in libs/subcircuit provide a library for solving the subcircuit isomorphism problem. It is written by C. Wolf and based on the Ullmann Subgraph Isomorphism Algorithm [Ull76]. It is used by the extract pass (see extract - find subcircuits and replace them with cells).