Bun has a bigint size limitation. It's 1_048_575 bits (1024 ** 2) or 131_072 Bytes.

The module.f.mjs exports two constants documenting this limit:

• maxBits = 1,048,575n — the maximum number of bits in a bigint value
• maxBytes = 131,072n — the maximum file size in bytes (equivalent to maxBits ÷ 8)

This limit applies to all bigint-backed types, including bit_vec and ReadFile effects. The ReadFile effect enforces this limit on file reads to ensure cross-runtime compatibility — files larger than 131,072 bytes will be rejected with a validation error.

For big numbers, about $2^{1,000,000}$:

For small numbers, about $2^{1,000}$:

Browser Test

For big numbers, about $2^{1,000,000}$:

For small numbers, about $2^{1,000}$:

See also https://medium.com/@sergeyshandar/improving-the-log2-algorithm-for-bigint-in-javascript-7e5692e7bf0b?sk=9ac18367f61b524704cc8d82707aed3d

For big numbers, about $2^{1,000,000}$:

For small numbers, about $2^{1,000}$:

Browser Test

For big numbers, about 2 ** 1_000_000:

For small numbers, 1 .. 2 ** 2_000:

Note: the benchmark was changed since 2024 and runs more tests. Compare only relative numbers.

The new log2 wins on Deno and Node (V8) but slightly loses on Bun (WebKit).

https://github.com/functionalscript/functionalscript/actions/runs/12521052013/job/34927599441?pr=346

Browser Test

benchmark.html

- wins.

log2 wins.