dec128

128-bit fixed-point decimal numbers in go.

Key Objectives / Features

• High performance
• Minimal or zero memory allocation
• Precision up to 19 decimal places
• Fixed size memory layout (128 bits)
• No panic or error arithmetics (use NaN instead)
• Immutability (methods return new instances)
• Basic arithmetic operations required for financial calculations (specifically for banking and accounting)
• Additional arithmetic operations for scientific calculations
• Easy to use
• Easy to inegrate with external systems (e.g. databases, accounting systems, JSON, etc.)
• Financially correct rounding
• Correct comparison of numbers encoded in different precisions (e.g. 1.0 == 1.00)
• Correct handling of NaN values (e.g. NaN + 1 = NaN)
• Conversion to canonical representation (e.g. 1.0000 -> 1)
• Conversion to fixed string representation (e.g. 1.0000 -> "1.0000")
• Conversion to human-readable string representation (e.g. 1.0000 -> "1")

Install

Run go get github.com/jokruger/dec128

Requirements

This library requires Go version >=1.23

Documentation

http://godoc.org/github.com/jokruger/dec128

Usage

package main

import (
    "fmt"
    "github.com/jokruger/dec128"
)

func main() {
    principal := dec128.FromString("1000.00")
    annualRate := dec128.FromString("5.0")
    days := 30

    dailyRate := annualRate.Div(dec128.FromInt64(365))
    dailyRate = dailyRate.Div(dec128.FromInt64(100))

    accruedInterest := principal.Mul(dailyRate).Mul(dec128.FromInt64(days)).RoundBank(2)

    fmt.Printf("Principal: %v\n", principal.StringFixed())
    fmt.Printf("Annual Interest Rate: %v\n", annualRate.String())
    fmt.Printf("Days: %v\n", days)
    fmt.Printf("Accrued Interest: %v\n", accruedInterest.String())

    total := principal.Add(accruedInterest).RoundBank(2)
    fmt.Printf("Total after %v days: %v\n", days, total.StringFixed())
}

Why not use other libraries?

There are several other libraries that provide decimal arithmetic in Go. However, most of them are either too slow, too memory-intensive, or lack the integration features required for financial applications. This library aims to provide a high-performance, low-memory, and easy-to-use alternative to existing libraries.

Benchmarks

The following benchmarks were run on a MacBook Pro (2019) with a 2.6 GHz 6-Core Intel Core i7 processor and 16 GB of RAM (https://github.com/jokruger/go-decimal-benchmark).

                                 parse (ns/op)  string (ns/op)     add (ns/op)     mul (ns/op)     div (ns/op)

dec128.Dec128                           14.024          33.683           9.975           6.569          35.116
udecimal.Decimal                        23.302          41.854          12.226          11.346          40.877
alpacadecimal.Decimal                   89.528          78.884         206.393          60.364         451.828
shopspring.Decimal                     152.263         169.300         218.909          65.241         428.002

Notes on Terminology

• Precision: The number of decimal places in a number. For example, 1.00 has a precision of 2 and 1.0000 has a precision of 4.
• Expontent: Same as precision, but in the context of low-level implementation details or Dec128 encoding.
• Canonical: The representation of a number with the minimum number of decimal places required to represent the number.

License

This project is licensed under the MIT License. See the LICENSE file for details.

Attribution

This project includes code derived from:

• A project licensed under the BSD 3-Clause License (Copyright © 2025 Quang).
• A project licensed under the MIT License (Copyright © 2019 Luke Champine).

See the LICENSE file for full license texts.