go-decimal

Fixed-point decimal arithmetic with a configurable Context (scale + rounding) and a compile-once expression engine.

Features

• Fixed-point decimal core: store scaled integers to avoid binary float drift
• Context controls output scale and rounding mode
• Expression compiler: tokenize + shunting-yard + RPN VM (compile once, eval fast)

Install

go get github.com/TimLai666/go-decimal

Decimal usage

ctx := decimal.Context{Scale: 2, Mode: decimal.RoundingModeHalfUp}

price := decimal.MustParse(ctx, "12.345") // 12.35
qty := decimal.MustParse(ctx, "2")

subtotal := decimal.Mul(ctx, price, qty) // 24.70

discount := decimal.MustParse(ctx, "1.01")

final := decimal.Sub(ctx, subtotal, discount)
fmt.Println(final.String()) // 23.69

Rounding modes

• RoundingModeDown: toward zero
• RoundingModeUp: away from zero
• RoundingModeHalfUp: halves away from zero

All operations normalize to Context.Scale.

Expression usage

ctx := decimal.Context{Scale: 2, Mode: decimal.RoundingModeHalfUp}

prog, err := expr.Compile("1.2 + x/3")
if err != nil {
    log.Fatal(err)
}

vars := expr.MapVars{
    "x": decimal.MustParse(ctx, "10"),
}

res, err := prog.Eval(ctx, vars)
if err != nil {
    log.Fatal(err)
}

fmt.Println(res.String()) // 4.53

Notes

• Fixed-point decimals: value = int / 10^scale
• Division is integer division with rounding to Context.Scale
• No exponent notation or math functions (sqrt, log, etc.)

Benchmarks

go test ./... -bench=. -benchmem