---
title: dankogai/swift-bigint-javascriptcore
framework: Swift Package Catalog
role: article
path: packages/dankogai/swift-bigint-javascriptcore
---

# dankogai/swift-bigint-javascriptcore

BigInt Implementation via JavaScriptCore

## Synopsis

```swift import JSCBigInt

// Integer literals of any size, thanks to StaticBigInt let n: JSBigInt = 123456789012345678901234567890123456789012345678901234567890

// A full SignedInteger: use it like any Swift integer let fact100 = (1...100).map { JSBigInt($0) }.reduce(1, *) JSBigInt(2).power(128)              // 340282366920938463463374607431768211456 (JSBigInt(1) << 100) >> 100         // 1 JSBigInt("deadbeef", radix: 16)!    // 3735928559 fact100.toString(radix: 36)         // "1cnfrwcnvxbzzicfd6…" Int(JSBigInt(42))                   // 42 — stdlib conversions just work Double(JSBigInt(1) << 100)          // 1.2676506002282294e+30 ```

## Usage

Add to your `Package.swift`:

```swift .package(url: "https://github.com/dankogai/swift-bigint-javascriptcore.git", branch: "main") ```

and `import JSCBigInt`.

## Features

- `JSBigInt` conforms to `SignedInteger` (hence `BinaryInteger`, `Numeric`,   `Comparable`, `Hashable`, `Strideable`…), so it works with generic   integer algorithms out of the box. - Integer literals use `StaticBigInt` — no precision loss, no strings needed. - Swift semantics throughout: `/` truncates toward zero, `%` takes the   dividend's sign, `>>` is an arithmetic (smart) shift, division by zero traps. - String conversion to and from any radix in `2...36`. - Exact conversions to and from `BinaryInteger` and `BinaryFloatingPoint`   types, including two's-complement `words` for stdlib interop. - `power(_:)` via the JS `**` operator, and modular exponentiation   `power(_:mod:)` with swift-bignum-compatible semantics (least   non-negative residue; a negative exponent takes the modular inverse). - `greatestCommonDivisor(with:)` and `squareRoot()` (integer square   root, floor), named and behaving like their swift-bignum and   attaswift/BigInt counterparts. - The whole primality kit, ported from swift-bignum with identical   verdicts: `isPrime` is tri-state — `false` and `true` are proofs   (below 2⁶⁴ via exhaustively-verified [Baillie-PSW], below   [A014233]'s last entry ≈3.3 × 10²⁴ via thirteen Miller-Rabin bases,   or for any Mersenne number via Lucas-Lehmer), `nil` means "probably   prime, unproven" with `isProbablePrime` (BPSW) holding that opinion   and `isSurelyPrime` giving both halves at once.  The building blocks   are public too: `millerRabinTest(base:)`, `isLucasProbablePrime`,   `isMersennePrime`, and `jacobiSymbol(_:)`.  `nextPrime`/`prevPrime`   walk to the neighboring primes (on the probable test, so they   terminate at any size), each walk in a single bridge crossing, and   `JSBigInt.primes` is the endless lazy sequence of them:   `Array(JSBigInt.primes.prefix(5))` is `[2, 3, 5, 7, 11]`.

[Baillie-PSW]: https://en.wikipedia.org/wiki/Baillie%E2%80%93PSW_primality_test

[A014233]: https://oeis.org/A014233 - `Codable` (encoded as a decimal string). - Thread-safe: values are immutable and JavaScriptCore serializes access   through the `JSVirtualMachine` lock.

## Caveats

- Apple platforms only (macOS, iOS, tvOS, visionOS). No Linux, no watchOS —   they lack JavaScriptCore. - Every operation crosses the Swift ⇄ JavaScriptCore bridge, so it is not a   speed demon for many small operations.  Large-number performance is   excellent, though — for 10k-digit multiplication it beats the pure-Swift   bignum libraries (attaswift/BigInt, dankogai/swift-bignum) severalfold,   since the heavy lifting happens inside JSC's optimized `BigInt`.   See [Benchmark.md](Benchmark.md) for numbers. - For serious work, consider [attaswift/BigInt] or [dankogai/swift-bignum] —   or [dankogai/swift-bigint-gmp], the identical API on GNU MP, which beats   all three (this one included) at nearly every size; its Benchmark.md races   the four together.  This package is a proof of concept that happens to be   practical.

[attaswift/BigInt]: https://github.com/attaswift/BigInt [dankogai/swift-bignum]: https://github.com/dankogai/swift-bignum [dankogai/swift-bigint-gmp]: https://github.com/dankogai/swift-bigint-gmp

## Prerequisite

Swift 5.9 or better, macOS 14 / iOS 17 or later.

## License

MIT. See [LICENSE](LICENSE).

## Package Metadata

Repository: dankogai/swift-bigint-javascriptcore

Default branch: main

README: README.md