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go-ruby-bigdecimal documentation

Ruby's BigDecimal arbitrary-precision decimals in pure Go — MRI-compatible, no cgo.

go-ruby-bigdecimal/bigdecimal is a faithful, pure-Go (zero cgo) reimplementation of Ruby's BigDecimal, matching reference Ruby (MRI) byte-for-byte. The module path is github.com/go-ruby-bigdecimal/bigdecimal.

It was extracted from rbgo's prelude/internals into a reusable standalone library: the module is standalone and importable by any Go program, and it is the backend bound into go-embedded-ruby by rbgo as a native module — just like go-ruby-regexp and go-ruby-erb. The dependency runs the other way: this library has no dependency on the Ruby runtime.

Status: arithmetic + rounding + formatting complete — MRI byte-exact

Faithful port of Ruby's BigDecimal: arbitrary-precision add / subtract / multiply, div / divmod honouring an explicit precision argument, the seven rounding modes (ROUND_UP, ROUND_DOWN, ROUND_HALF_UP, ROUND_HALF_DOWN, ROUND_HALF_EVEN, ROUND_CEILING, ROUND_FLOOR), both the engineering ("E") and plain ("F") to_s forms, and NaN / +Infinity / -Infinity handling. Validated by a differential oracle against the system ruby / bigdecimal — values compared byte-for-byte — at 100% coverage, gofmt + go vet clean, CI green across the six 64-bit Go targets and three OSes.

Quick taste

a := bigdecimal.New("0.1")
b := bigdecimal.New("0.2")
s := a.Add(b).String()              // "0.3e0"
q := a.DivPrec(b, 10)               // division to 10 significant digits

Repositories

Repo What it is
bigdecimal the library — Ruby's BigDecimal in pure Go
docs this documentation site (MkDocs Material, versioned with mike)
go-ruby-bigdecimal.github.io the organization landing page (Hugo)
brand logo and brand assets

Principles

  • Pure Go, CGO_ENABLED=0 — trivial cross-compilation, a single static binary, no C toolchain.
  • MRI byte-exact. Output matches reference Ruby exactly, not approximately, validated by a differential oracle against the ruby binary.
  • Standalone & reusable. Extracted from rbgo's internals; no dependency on the Ruby runtime — the dependency runs the other way.
  • 100% test coverage is the target, enforced as a CI gate, across 6 arches and 3 OSes.

Where to go next

  • Why pure Go — why this slice of Ruby is deterministic enough to live as a standalone, interpreter-independent Go library.
  • Usage & API — the public surface and worked examples.
  • Roadmap — what is done and what is downstream by design.

Source lives at github.com/go-ruby-bigdecimal/bigdecimal.