APInt - Arbitrary Precision Integers for Rust

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Development in progress: The implementation has not been finished, is unstable and may not work.

Arbitrary Precision Integers (APInt) are a way to handle integers that have an arbitrary but fixed (on runtime) bit-width and offer modulo arithmetic similar to the primitive machine integers.

This library and its API are based on the popular LLVM APInt support library which is used quite heavily within the compiler and compiler-based tools. To model machine numbers during the compilation process.

Uses cases may vary greatly - the initial motivation for building this library was for use in an SMT solver that operates mainly on the theory of bitvectors.

Internals

The design focus was for efficiency and stability. APInt instances are space-optimized for bit-widths equal to or smaller than 64 bits - only larger bit-widths require dynamic memory allocation! For small bit-widths a compute buffer of 128 bits is used which is realized by the currently unstable Rust language feature i128 that will hopefully be stabilized soon as this is the only stable channel blocker so far.

The public interface functions avoid panicing and promote returning Results and decent quality error codes instead. Some convenience arithmetic operators are overloaded in the cases where it is useful - those do panic as it is convenient for them to be homogenous in input and output types.

Current State

Currently only a part of the internal implementation is done. Especially the implementation of the large APInt's with bit-widths greater than 64 bits are lacking a lot of implementation code. However, this should not be a major problem since this crate is so similar to the well known APInt of LLVM as already stated above.

It is planned to add SAPInt (Signed Arbitrary Precision Integer) an optional interface on top of APInt to further add some signedness information. This will behave similar to LLVM's APSInt type.

Planned Features

• Full APInt implementation with focus on efficiency and stability
• SAPInt interface layer on top of APInt to add signess information
• Extensive test suite to provide a decent quality implementation guarantee
• Hopefully soon on stable - as soon as i128 is stabilized

License

Licensed under either of

• Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Dual licence: