README

decimal

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Arbitrary-precision fixed-point decimal numbers in go.

Note: Decimal library can "only" represent numbers with a maximum of 2^31 digits after the decimal point.

Features

  • The zero-value is 0, and is safe to use without initialization
  • Addition, subtraction, multiplication with no loss of precision
  • Division with specified precision
  • Database/sql serialization/deserialization
  • JSON and XML serialization/deserialization

Install

Run go get github.com/shopspring/decimal

Requirements

Decimal library requires Go version >=1.7

Usage

package main

import (
	"fmt"
	"github.com/shopspring/decimal"
)

func main() {
	price, err := decimal.NewFromString("136.02")
	if err != nil {
		panic(err)
	}

	quantity := decimal.NewFromInt(3)

	fee, _ := decimal.NewFromString(".035")
	taxRate, _ := decimal.NewFromString(".08875")

	subtotal := price.Mul(quantity)

	preTax := subtotal.Mul(fee.Add(decimal.NewFromFloat(1)))

	total := preTax.Mul(taxRate.Add(decimal.NewFromFloat(1)))

	fmt.Println("Subtotal:", subtotal)                      // Subtotal: 408.06
	fmt.Println("Pre-tax:", preTax)                         // Pre-tax: 422.3421
	fmt.Println("Taxes:", total.Sub(preTax))                // Taxes: 37.482861375
	fmt.Println("Total:", total)                            // Total: 459.824961375
	fmt.Println("Tax rate:", total.Sub(preTax).Div(preTax)) // Tax rate: 0.08875
}

Documentation

http://godoc.org/github.com/shopspring/decimal

Production Usage

  • Spring, since August 14, 2014.
  • If you are using this in production, please let us know!

FAQ

Why don't you just use float64?

Because float64 (or any binary floating point type, actually) can't represent numbers such as 0.1 exactly.

Consider this code: http://play.golang.org/p/TQBd4yJe6B You might expect that it prints out 10, but it actually prints 9.999999999999831. Over time, these small errors can really add up!

Why don't you just use big.Rat?

big.Rat is fine for representing rational numbers, but Decimal is better for representing money. Why? Here's a (contrived) example:

Let's say you use big.Rat, and you have two numbers, x and y, both representing 1/3, and you have z = 1 - x - y = 1/3. If you print each one out, the string output has to stop somewhere (let's say it stops at 3 decimal digits, for simplicity), so you'll get 0.333, 0.333, and 0.333. But where did the other 0.001 go?

Here's the above example as code: http://play.golang.org/p/lCZZs0w9KE

With Decimal, the strings being printed out represent the number exactly. So, if you have x = y = 1/3 (with precision 3), they will actually be equal to 0.333, and when you do z = 1 - x - y, z will be equal to .334. No money is unaccounted for!

You still have to be careful. If you want to split a number N 3 ways, you can't just send N/3 to three different people. You have to pick one to send N - (2/3*N) to. That person will receive the fraction of a penny remainder.

But, it is much easier to be careful with Decimal than with big.Rat.

Why isn't the API similar to big.Int's?

big.Int's API is built to reduce the number of memory allocations for maximal performance. This makes sense for its use-case, but the trade-off is that the API is awkward and easy to misuse.

For example, to add two big.Ints, you do: z := new(big.Int).Add(x, y). A developer unfamiliar with this API might try to do z := a.Add(a, b). This modifies a and sets z as an alias for a, which they might not expect. It also modifies any other aliases to a.

Here's an example of the subtle bugs you can introduce with big.Int's API: https://play.golang.org/p/x2R_78pa8r

In contrast, it's difficult to make such mistakes with decimal. Decimals behave like other go numbers types: even though a = b will not deep copy b into a, it is impossible to modify a Decimal, since all Decimal methods return new Decimals and do not modify the originals. The downside is that this causes extra allocations, so Decimal is less performant. My assumption is that if you're using Decimals, you probably care more about correctness than performance.

License

The MIT License (MIT)

This is a heavily modified fork of fpd.Decimal, which was also released under the MIT License.

Documentation

Overview

Package decimal implements an arbitrary precision fixed-point decimal.

The zero-value of a Decimal is 0, as you would expect.

The best way to create a new Decimal is to use decimal.NewFromString, ex:

n, err := decimal.NewFromString("-123.4567")
n.String() // output: "-123.4567"

To use Decimal as part of a struct:

type Struct struct {
    Number Decimal
}

Note: This can "only" represent numbers with a maximum of 2^31 digits after the decimal point.

Index

Examples

Constants

This section is empty.

Variables

View Source
var DivisionPrecision = 16

DivisionPrecision is the number of decimal places in the result when it doesn't divide exactly.

Example:

d1 := decimal.NewFromFloat(2).Div(decimal.NewFromFloat(3))
d1.String() // output: "0.6666666666666667"
d2 := decimal.NewFromFloat(2).Div(decimal.NewFromFloat(30000))
d2.String() // output: "0.0000666666666667"
d3 := decimal.NewFromFloat(20000).Div(decimal.NewFromFloat(3))
d3.String() // output: "6666.6666666666666667"
decimal.DivisionPrecision = 3
d4 := decimal.NewFromFloat(2).Div(decimal.NewFromFloat(3))
d4.String() // output: "0.667"
View Source
var MarshalJSONWithoutQuotes = false

MarshalJSONWithoutQuotes should be set to true if you want the decimal to be JSON marshaled as a number, instead of as a string. WARNING: this is dangerous for decimals with many digits, since many JSON unmarshallers (ex: Javascript's) will unmarshal JSON numbers to IEEE 754 double-precision floating point numbers, which means you can potentially silently lose precision.

View Source
var Zero = New(0, 1)

Zero constant, to make computations faster. Zero should never be compared with == or != directly, please use decimal.Equal or decimal.Cmp instead.

Functions

func RescalePair

func RescalePair(d1 Decimal, d2 Decimal) (Decimal, Decimal)

RescalePair rescales two decimals to common exponential value (minimal exp of both decimals)

Types

type Decimal

type Decimal struct {
	// contains filtered or unexported fields
}

Decimal represents a fixed-point decimal. It is immutable. number = value * 10 ^ exp

func Avg

func Avg(first Decimal, rest ...Decimal) Decimal

Avg returns the average value of the provided first and rest Decimals

func Max

func Max(first Decimal, rest ...Decimal) Decimal

Max returns the largest Decimal that was passed in the arguments.

To call this function with an array, you must do:

Max(arr[0], arr[1:]...)

This makes it harder to accidentally call Max with 0 arguments.

func Min

func Min(first Decimal, rest ...Decimal) Decimal

Min returns the smallest Decimal that was passed in the arguments.

To call this function with an array, you must do:

Min(arr[0], arr[1:]...)

This makes it harder to accidentally call Min with 0 arguments.

func New

func New(value int64, exp int32) Decimal

New returns a new fixed-point decimal, value * 10 ^ exp.

func NewFromBigInt

func NewFromBigInt(value *big.Int, exp int32) Decimal

NewFromBigInt returns a new Decimal from a big.Int, value * 10 ^ exp

func NewFromFloat

func NewFromFloat(value float64) Decimal

NewFromFloat converts a float64 to Decimal.

The converted number will contain the number of significant digits that can be represented in a float with reliable roundtrip. This is typically 15 digits, but may be more in some cases. See https://www.exploringbinary.com/decimal-precision-of-binary-floating-point-numbers/ for more information.

For slightly faster conversion, use NewFromFloatWithExponent where you can specify the precision in absolute terms.

NOTE: this will panic on NaN, +/-inf

Example
Output:

123.123123123123
0.123123123123123
-10000000000000

func NewFromFloat32

func NewFromFloat32(value float32) Decimal

NewFromFloat32 converts a float32 to Decimal.

The converted number will contain the number of significant digits that can be represented in a float with reliable roundtrip. This is typically 6-8 digits depending on the input. See https://www.exploringbinary.com/decimal-precision-of-binary-floating-point-numbers/ for more information.

For slightly faster conversion, use NewFromFloatWithExponent where you can specify the precision in absolute terms.

NOTE: this will panic on NaN, +/-inf

Example
Output:

123.12312
0.123123124
-10000000000000

func NewFromFloatWithExponent

func NewFromFloatWithExponent(value float64, exp int32) Decimal

NewFromFloatWithExponent converts a float64 to Decimal, with an arbitrary number of fractional digits.

Example:

NewFromFloatWithExponent(123.456, -2).String() // output: "123.46"

func NewFromInt

func NewFromInt(value int64) Decimal

NewFromInt converts a int64 to Decimal.

Example:

NewFromInt(123).String() // output: "123"
NewFromInt(-10).String() // output: "-10"

func NewFromInt32

func NewFromInt32(value int32) Decimal

NewFromInt32 converts a int32 to Decimal.

Example:

NewFromInt(123).String() // output: "123"
NewFromInt(-10).String() // output: "-10"

func NewFromString

func NewFromString(value string) (Decimal, error)

NewFromString returns a new Decimal from a string representation. Trailing zeroes are not trimmed.

Example:

d, err := NewFromString("-123.45")
d2, err := NewFromString(".0001")
d3, err := NewFromString("1.47000")

func RequireFromString

func RequireFromString(value string) Decimal

RequireFromString returns a new Decimal from a string representation or panics if NewFromString would have returned an error.

Example:

d := RequireFromString("-123.45")
d2 := RequireFromString(".0001")

func Sum

func Sum(first Decimal, rest ...Decimal) Decimal

Sum returns the combined total of the provided first and rest Decimals

func (Decimal) Abs

func (d Decimal) Abs() Decimal

Abs returns the absolute value of the decimal.

func (Decimal) Add

func (d Decimal) Add(d2 Decimal) Decimal

Add returns d + d2.

func (Decimal) Atan

func (d Decimal) Atan() Decimal

Atan returns the arctangent, in radians, of x.

func (Decimal) BigFloat

func (d Decimal) BigFloat() *big.Float

BigFloat returns decimal as BigFloat. Be aware that casting decimal to BigFloat might cause a loss of precision.

func (Decimal) BigInt

func (d Decimal) BigInt() *big.Int

BigInt returns integer component of the decimal as a BigInt.

func (Decimal) Ceil

func (d Decimal) Ceil() Decimal

Ceil returns the nearest integer value greater than or equal to d.

func (Decimal) Cmp

func (d Decimal) Cmp(d2 Decimal) int

Cmp compares the numbers represented by d and d2 and returns:

-1 if d <  d2
 0 if d == d2
+1 if d >  d2

func (Decimal) Coefficient

func (d Decimal) Coefficient() *big.Int

Coefficient returns the coefficient of the decimal. It is scaled by 10^Exponent()

func (Decimal) Cos

func (d Decimal) Cos() Decimal

Cos returns the cosine of the radian argument x.

func (Decimal) Div

func (d Decimal) Div(d2 Decimal) Decimal

Div returns d / d2. If it doesn't divide exactly, the result will have DivisionPrecision digits after the decimal point.

func (Decimal) DivRound

func (d Decimal) DivRound(d2 Decimal, precision int32) Decimal

DivRound divides and rounds to a given precision i.e. to an integer multiple of 10^(-precision)

for a positive quotient digit 5 is rounded up, away from 0
if the quotient is negative then digit 5 is rounded down, away from 0

Note that precision<0 is allowed as input.

func (Decimal) Equal

func (d Decimal) Equal(d2 Decimal) bool

Equal returns whether the numbers represented by d and d2 are equal.

func (Decimal) Equals

func (d Decimal) Equals(d2 Decimal) bool

Equals is deprecated, please use Equal method instead

func (Decimal) Exponent

func (d Decimal) Exponent() int32

Exponent returns the exponent, or scale component of the decimal.

func (Decimal) Float64

func (d Decimal) Float64() (f float64, exact bool)

Float64 returns the nearest float64 value for d and a bool indicating whether f represents d exactly. For more details, see the documentation for big.Rat.Float64

func (Decimal) Floor

func (d Decimal) Floor() Decimal

Floor returns the nearest integer value less than or equal to d.

func (*Decimal) GobDecode

func (d *Decimal) GobDecode(data []byte) error

GobDecode implements the gob.GobDecoder interface for gob serialization.

func (Decimal) GobEncode

func (d Decimal) GobEncode() ([]byte, error)

GobEncode implements the gob.GobEncoder interface for gob serialization.

func (Decimal) GreaterThan

func (d Decimal) GreaterThan(d2 Decimal) bool

GreaterThan (GT) returns true when d is greater than d2.

func (Decimal) GreaterThanOrEqual

func (d Decimal) GreaterThanOrEqual(d2 Decimal) bool

GreaterThanOrEqual (GTE) returns true when d is greater than or equal to d2.

func (Decimal) IntPart

func (d Decimal) IntPart() int64

IntPart returns the integer component of the decimal.

func (Decimal) IsNegative

func (d Decimal) IsNegative() bool

IsNegative return

true if d < 0
false if d == 0
false if d > 0

func (Decimal) IsPositive

func (d Decimal) IsPositive() bool

IsPositive return

true if d > 0
false if d == 0
false if d < 0

func (Decimal) IsZero

func (d Decimal) IsZero() bool

IsZero return

true if d == 0
false if d > 0
false if d < 0

func (Decimal) LessThan

func (d Decimal) LessThan(d2 Decimal) bool

LessThan (LT) returns true when d is less than d2.

func (Decimal) LessThanOrEqual

func (d Decimal) LessThanOrEqual(d2 Decimal) bool

LessThanOrEqual (LTE) returns true when d is less than or equal to d2.

func (Decimal) MarshalBinary

func (d Decimal) MarshalBinary() (data []byte, err error)

MarshalBinary implements the encoding.BinaryMarshaler interface.

func (Decimal) MarshalJSON

func (d Decimal) MarshalJSON() ([]byte, error)

MarshalJSON implements the json.Marshaler interface.

func (Decimal) MarshalText

func (d Decimal) MarshalText() (text []byte, err error)

MarshalText implements the encoding.TextMarshaler interface for XML serialization.

func (Decimal) Mod

func (d Decimal) Mod(d2 Decimal) Decimal

Mod returns d % d2.

func (Decimal) Mul

func (d Decimal) Mul(d2 Decimal) Decimal

Mul returns d * d2.

func (Decimal) Neg

func (d Decimal) Neg() Decimal

Neg returns -d.

func (Decimal) Pow

func (d Decimal) Pow(d2 Decimal) Decimal

Pow returns d to the power d2

func (Decimal) QuoRem

func (d Decimal) QuoRem(d2 Decimal, precision int32) (Decimal, Decimal)

QuoRem does divsion with remainder d.QuoRem(d2,precision) returns quotient q and remainder r such that

d = d2 * q + r, q an integer multiple of 10^(-precision)
0 <= r < abs(d2) * 10 ^(-precision) if d>=0
0 >= r > -abs(d2) * 10 ^(-precision) if d<0

Note that precision<0 is allowed as input.

func (Decimal) Rat

func (d Decimal) Rat() *big.Rat

Rat returns a rational number representation of the decimal.

func (Decimal) Round

func (d Decimal) Round(places int32) Decimal

Round rounds the decimal to places decimal places. If places < 0, it will round the integer part to the nearest 10^(-places).

Example:

NewFromFloat(5.45).Round(1).String() // output: "5.5"
NewFromFloat(545).Round(-1).String() // output: "550"

func (Decimal) RoundBank

func (d Decimal) RoundBank(places int32) Decimal

RoundBank rounds the decimal to places decimal places. If the final digit to round is equidistant from the nearest two integers the rounded value is taken as the even number

If places < 0, it will round the integer part to the nearest 10^(-places).

Examples:

NewFromFloat(5.45).Round(1).String() // output: "5.4"
NewFromFloat(545).Round(-1).String() // output: "540"
NewFromFloat(5.46).Round(1).String() // output: "5.5"
NewFromFloat(546).Round(-1).String() // output: "550"
NewFromFloat(5.55).Round(1).String() // output: "5.6"
NewFromFloat(555).Round(-1).String() // output: "560"

func (Decimal) RoundCash

func (d Decimal) RoundCash(interval uint8) Decimal

RoundCash aka Cash/Penny/öre rounding rounds decimal to a specific interval. The amount payable for a cash transaction is rounded to the nearest multiple of the minimum currency unit available. The following intervals are available: 5, 10, 25, 50 and 100; any other number throws a panic.

  5:   5 cent rounding 3.43 => 3.45
 10:  10 cent rounding 3.45 => 3.50 (5 gets rounded up)
 25:  25 cent rounding 3.41 => 3.50
 50:  50 cent rounding 3.75 => 4.00
100: 100 cent rounding 3.50 => 4.00

For more details: https://en.wikipedia.org/wiki/Cash_rounding

func (*Decimal) Scan

func (d *Decimal) Scan(value interface{}) error

Scan implements the sql.Scanner interface for database deserialization.

func (Decimal) Shift

func (d Decimal) Shift(shift int32) Decimal

Shift shifts the decimal in base 10. It shifts left when shift is positive and right if shift is negative. In simpler terms, the given value for shift is added to the exponent of the decimal.

func (Decimal) Sign

func (d Decimal) Sign() int

Sign returns:

-1 if d <  0
 0 if d == 0
+1 if d >  0

func (Decimal) Sin

func (d Decimal) Sin() Decimal

Sin returns the sine of the radian argument x.

func (Decimal) String

func (d Decimal) String() string

String returns the string representation of the decimal with the fixed point.

Example:

d := New(-12345, -3)
println(d.String())

Output:

-12.345

func (Decimal) StringFixed

func (d Decimal) StringFixed(places int32) string

StringFixed returns a rounded fixed-point string with places digits after the decimal point.

Example:

NewFromFloat(0).StringFixed(2) // output: "0.00"
NewFromFloat(0).StringFixed(0) // output: "0"
NewFromFloat(5.45).StringFixed(0) // output: "5"
NewFromFloat(5.45).StringFixed(1) // output: "5.5"
NewFromFloat(5.45).StringFixed(2) // output: "5.45"
NewFromFloat(5.45).StringFixed(3) // output: "5.450"
NewFromFloat(545).StringFixed(-1) // output: "550"

func (Decimal) StringFixedBank

func (d Decimal) StringFixedBank(places int32) string

StringFixedBank returns a banker rounded fixed-point string with places digits after the decimal point.

Example:

NewFromFloat(0).StringFixedBank(2) // output: "0.00"
NewFromFloat(0).StringFixedBank(0) // output: "0"
NewFromFloat(5.45).StringFixedBank(0) // output: "5"
NewFromFloat(5.45).StringFixedBank(1) // output: "5.4"
NewFromFloat(5.45).StringFixedBank(2) // output: "5.45"
NewFromFloat(5.45).StringFixedBank(3) // output: "5.450"
NewFromFloat(545).StringFixedBank(-1) // output: "540"

func (Decimal) StringFixedCash

func (d Decimal) StringFixedCash(interval uint8) string

StringFixedCash returns a Swedish/Cash rounded fixed-point string. For more details see the documentation at function RoundCash.

func (Decimal) StringScaled

func (d Decimal) StringScaled(exp int32) string

StringScaled first scales the decimal then calls .String() on it. NOTE: buggy, unintuitive, and DEPRECATED! Use StringFixed instead.

func (Decimal) Sub

func (d Decimal) Sub(d2 Decimal) Decimal

Sub returns d - d2.

func (Decimal) Tan

func (d Decimal) Tan() Decimal

Tan returns the tangent of the radian argument x.

func (Decimal) Truncate

func (d Decimal) Truncate(precision int32) Decimal

Truncate truncates off digits from the number, without rounding.

NOTE: precision is the last digit that will not be truncated (must be >= 0).

Example:

decimal.NewFromString("123.456").Truncate(2).String() // "123.45"

func (*Decimal) UnmarshalBinary

func (d *Decimal) UnmarshalBinary(data []byte) error

UnmarshalBinary implements the encoding.BinaryUnmarshaler interface. As a string representation is already used when encoding to text, this method stores that string as []byte

func (*Decimal) UnmarshalJSON

func (d *Decimal) UnmarshalJSON(decimalBytes []byte) error

UnmarshalJSON implements the json.Unmarshaler interface.

func (*Decimal) UnmarshalText

func (d *Decimal) UnmarshalText(text []byte) error

UnmarshalText implements the encoding.TextUnmarshaler interface for XML deserialization.

func (Decimal) Value

func (d Decimal) Value() (driver.Value, error)

Value implements the driver.Valuer interface for database serialization.

type NullDecimal

type NullDecimal struct {
	Decimal Decimal
	Valid   bool
}

NullDecimal represents a nullable decimal with compatibility for scanning null values from the database.

func (NullDecimal) MarshalJSON

func (d NullDecimal) MarshalJSON() ([]byte, error)

MarshalJSON implements the json.Marshaler interface.

func (*NullDecimal) Scan

func (d *NullDecimal) Scan(value interface{}) error

Scan implements the sql.Scanner interface for database deserialization.

func (*NullDecimal) UnmarshalJSON

func (d *NullDecimal) UnmarshalJSON(decimalBytes []byte) error

UnmarshalJSON implements the json.Unmarshaler interface.

func (NullDecimal) Value

func (d NullDecimal) Value() (driver.Value, error)

Value implements the driver.Valuer interface for database serialization.