Be Precise: using floats to represent currency is almost criminal. — Robert.C.Martin, "Clean Code" p.301
- as fast as
int64 - no
floatin parsing nor printing, does not leak precision ISO 4217currency- block mismatched currency arithmetics
- 100 LOC
- fuzz tests
var BuySP500Price = fpmoney.FromInt(9000, fpmoney.SGD)
input := []byte(`{"sp500": {"amount": 9000.02, "currency": "SGD"}}`)
type Stonks struct {
SP500 fpmoney.Amount `json:"sp500"`
}
var v Stonks
if err := json.Unmarshal(input, &v); err != nil {
log.Fatal(err)
}
amountToBuy := fpmoney.FromInt(0, fpmoney.SGD)
if v.SP500.GreaterThan(BuySP500Price) {
amountToBuy = amountToBuy.Add(v.SP500.Mul(2))
}
fmt.Println(amountToBuy)
// Output: 18000.04 SGDSome denominations have very low fractions.
Storing them int64 you would get.
BTCsatoshi is1 BTC = 100,000,000 satoshi, which is still enough for ~92,233,720,368 BTC.ETHwei is1 ETH = 1,000,000,000,000,000,000 wei, which is ~9 ETH. If you deal with wei, you may considerbigintor multipleint64. In fact, official Ethereum code is in Go and it is using bigint (code).
$ go test -bench=. -benchmem . > fpmoney.bench
$ go test -bench=. -benchmem ./internal/bench/float32 > float32.bench
$ go test -bench=. -benchmem ./internal/bench/int > int.bench
$ benchstat -split="XYZ" int.bench float32.bench fpmoney.bench
name \ time/op int.bench float32.bench fpmoney.bench
JSONUnmarshal/small-16 383ns ± 0% 408ns ± 0% 294ns ± 0%
JSONUnmarshal/large-16 436ns ± 0% 473ns ± 0% 365ns ± 0%
JSONMarshal/small-16 115ns ± 0% 158ns ± 0% 226ns ± 0%
JSONMarshal/large-16 112ns ± 0% 146ns ± 0% 272ns ± 0%
name \ alloc/op int.bench float32.bench fpmoney.bench
JSONUnmarshal/small-16 268B ± 0% 270B ± 0% 198B ± 0%
JSONUnmarshal/large-16 272B ± 0% 288B ± 0% 216B ± 0%
JSONMarshal/small-16 57.0B ± 0% 66.0B ± 0% 160.0B ± 0%
JSONMarshal/large-16 72.0B ± 0% 72.0B ± 0% 176.0B ± 0%
name \ allocs/op int.bench float32.bench fpmoney.bench
JSONUnmarshal/small-16 6.00 ± 0% 6.00 ± 0% 3.00 ± 0%
JSONUnmarshal/large-16 6.00 ± 0% 6.00 ± 0% 3.00 ± 0%
JSONMarshal/small-16 2.00 ± 0% 2.00 ± 0% 3.00 ± 0%
JSONMarshal/large-16 2.00 ± 0% 2.00 ± 0% 3.00 ± 0%goos: darwin
goarch: arm64
pkg: github.com/nikolaydubina/fpmoney
BenchmarkArithmetic/add_x1-16 1000000000 0.54 ns/op 0 B/op 0 allocs/op
BenchmarkArithmetic/add_x100-16 26382420 44.42 ns/op 0 B/op 0 allocs/op
PASS
ok github.com/nikolaydubina/fpmoney 14.200s- ferdypruis/iso4217 was a good inspiration and reference material. it was used in early version as well. it is well maintained and fast library for currencies.
github.com/shopspring/decimal: fixed precision; faster printing/parsing/arithmetics; currency handlinggithub.com/Rhymond/go-money: does not usefloatorinterface{}in parsing; currency is enumgithub.com/ferdypruis/iso4217: skipped deprecated currencies to fit intouint8and smaller struct size