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Zero-allocation, panic-free decimal arithmetic for HFT-grade Go. No big.Int, no GC pressure, fastest in its class.

5 starsGo

I vibe coded the fastest Decimal Go lib

by alexandroskyr·Jun 12, 2026·1 point·0 comments
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AI Analysis

●●●BangerWizardryBig Brain

Reciprocal division trick beats udecimal by 35% with zero heap allocations.

Strengths
  • •Möller–Granlund 2-by-1 division replaces hardware DIV with precomputed magics
  • •testing.AllocsPerRun gates enforce zero allocations on every code path
  • •Differential fuzz testing against shopspring/decimal proves bit-exact correctness
Weaknesses
  • •128-bit coefficient limits precision to 39 digits, may not suit all domains
  • •Requires Go 1.26+, excludes users on older LTS versions
Target Audience

Go developers building latency-critical systems (HFT, trading, billing)

Similar To

shopspring/decimal · quagmt/udecimal

Post Description

A zero-allocation Go decimal library with no big.Int fallback — 128-bit fixed-point arithmetic that benchstats ~35% faster than the fastest existing library, with exact alloc counts and overflow correctness enforced by the test suite.

The fun part was making it fast: every division by a power of ten (rescaling, rounding, formatting) is done with precomputed multiply-high reciprocals instead of hardware DIV — the Möller–Granlund 2-by-1 trick plus magic constants, all generated and re-proven against big.Int. On my M1 Pro it benchstats ~35% faster (geomean) than udecimal, the fastest library I could find, and ~9x faster than shopspring.

How: Claude Code with Ultracode + Fable 5 for 12hours

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