decimal

package module
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 Go to latest Published: Apr 11, 2024 License: BSD-3-Clause Imports: 16 Imported by: 509

README

decimal Build Status GoDoc

decimal implements arbitrary precision, decimal floating-point numbers, per the General Decimal Arithmetic specification.

Features

  • Useful zero values. The zero value of a decimal.Big is 0, just like math/big.

  • Multiple operating modes. Different operating modes allow you to tailor the package's behavior to your needs. The GDA mode strictly implements the GDA specification, while the Go mode implements familiar Go idioms.

  • High performance. decimal is consistently one of the fastest arbitrary-precision decimal floating-point libraries, regardless of language.

  • An extensive math library. The math/ subpackage implements elementary and trigonometric functions, continued fractions, and more.

  • A familiar, idiomatic API. decimal's API follows math/big's API, so there isn't a steep learning curve.

Installation

go get github.com/ericlagergren/decimal

Documentation

GoDoc

Versioning

decimal uses Semantic Versioning. The current version is 3.3.1.

decimal only explicitly supports the two most recent major Go 1.X versions.

License

BSD 3-clause

Documentation

Overview

Package decimal provides a high-performance, arbitrary precision, floating-point decimal library.

Overview

This package provides floating-point decimal numbers, useful for financial programming or calculations where a larger, more accurate representation of a number is required.

In addition to basic arithmetic operations (addition, subtraction, multiplication, and division) this package offers various mathematical functions, including the exponential function, various logarithms, and the ability to compute continued fractions.

While lean, this package is full of features. It implements interfaces like “fmt.Formatter” and intuitively utilizes verbs and flags as described in the “fmt” package. (Also included: “fmt.Scanner”, “fmt.Stringer”, “encoding.TextUnmarshaler”, and “encoding.TextMarshaler”.)

It allows users to specific explicit contexts for arithmetic operations, but doesn't require it. It provides access to NaN payloads and is more lenient when parsing a decimal from a string than the GDA specification requires.

API interfaces have been changed slightly to work more seamlessly with existing Go programs. For example, many “Quantize” implementations require a decimal as both the receiver and argument which isn't very user friendly. Instead, this library accepts a simple “int” which can be derived from an existing decimal if required.

It contains two modes of operation designed to make transitioning to various GDA "quirks" (like always rounding lossless operations) easier. 

GDA: strictly adhere to the GDA specification (default)
Go: utilize Go idioms, more flexibility

Goals

There are three primary goals of this library:

  1. Correctness

By adhering to the General Decimal Arithmetic specification, this package has a well-defined structure for its arithmetic operations.

  1. Performance

Decimal libraries are inherently slow; this library works diligently to minimize memory allocations and utilize efficient algorithms. Performance regularly benchmarks as fast or faster than many other popular decimal libraries.

  1. Ease of use

Libraries should be intuitive and work out of the box without having to configure too many settings; however, precise settings should still be available.

Usage

The following type is supported: 

Big decimal numbers

The zero value for a Big corresponds with 0, meaning all the following are valid: 

var x Big
y := new(Big)
z := &Big{}

Method naming is the same as math/big's, meaning: 

func (z *T) SetV(v V) *T          // z = v
func (z *T) Unary(x *T) *T        // z = unary x
func (z *T) Binary(x, y *T) *T    // z = x binary y
func (x *T) Pred() P              // p = pred(x)

In general, its conventions mirror math/big's. It is suggested to read the math/big package comments to gain an understanding of this package's conventions.

Arguments to Binary and Unary methods are allowed to alias, so the following is valid: 

x := New(1, 0)
x.Add(x, x) // x == 2

y := New(1, 0)
y.FMA(y, x, y) // y == 3

Unless otherwise specified, the only argument that will be modified is the result (“z”). This means the following is valid and race-free: 

x := New(1, 0)
var g1, g2 Big

go func() { g1.Add(x, x) }()
go func() { g2.Add(x, x) }()

But this is not: 

x := New(1, 0)
var g Big

go func() { g.Add(x, x) }() // BAD! RACE CONDITION!
go func() { g.Add(x, x) }() // BAD! RACE CONDITION!

Index

Examples

Constants

View Source 
const (
	// Radix is the base in which decimal arithmetic is
	// performed.
	Radix = 10

	// IsCanonical is true since Big decimals are always
	// normalized.
	IsCanonical = true
)
View Source 
const (
	MaxScale           = c.MaxScale       // largest allowed scale.
	MinScale           = -MaxScale        // smallest allowed scale.
	MaxPrecision       = MaxScale         // largest allowed Context precision.
	MinPrecision       = 1                // smallest allowed Context precision.
	UnlimitedPrecision = MaxPrecision + 1 // no precision, but may error.
	DefaultPrecision   = 16               // default precision for literals.
)

Precision and scale limits.

Variables

View Source 
var (
	// Context32 is the IEEE 754R Decimal32 format.
	Context32 = Context{
		Precision:     7,
		RoundingMode:  ToNearestEven,
		OperatingMode: GDA,
		Traps:         ^(Inexact | Rounded | Subnormal),
		MaxScale:      96,
		MinScale:      -95,
	}

	// Context64 is the IEEE 754R Decimal64 format.
	Context64 = Context{
		Precision:     16,
		RoundingMode:  ToNearestEven,
		OperatingMode: GDA,
		Traps:         ^(Inexact | Rounded | Subnormal),
		MaxScale:      384,
		MinScale:      -383,
	}

	// Context128 is the IEEE 754R Decimal128 format.
	Context128 = Context{
		Precision:     34,
		RoundingMode:  ToNearestEven,
		OperatingMode: GDA,
		Traps:         ^(Inexact | Rounded | Subnormal),
		MaxScale:      6144,
		MinScale:      -6143,
	}

	// ContextUnlimited provides unlimited precision decimals.
	ContextUnlimited = Context{
		Precision:     UnlimitedPrecision,
		RoundingMode:  ToNearestEven,
		OperatingMode: GDA,
		Traps:         ^(Inexact | Rounded | Subnormal),
		MaxScale:      MaxScale,
		MinScale:      MinScale,
	}
)

The following Contexts are based on IEEE 754R. Each Context's RoundingMode is ToNearestEven, OperatingMode is GDA, and traps are set to every exception other than Inexact, Rounded, and Subnormal.

View Source 
var Regexp = regexp.MustCompile(`(?i)(([+-]?(\d+\.\d*|\.?\d+)([eE][+-]?\d+)?)|(inf(infinity)?))|([+-]?([sq]?nan\d*))`)

Regexp matches any valid string representing a decimal that can be passed to SetString.

Functions

func Raw 

func Raw(x *Big) (*uint64, *big.Int)

Raw directly returns x's raw compact and unscaled values.

Caveat emptor: neither are guaranteed to be valid. Raw is intended to support missing functionality outside this package and should generally be avoided. Additionally, Raw is the only part of this package's API that is not guaranteed to remain stable. This means the function could change or disappear at any time, even across minor version numbers.

Types

type Big 

type Big struct {
	// Context is the decimal's unique contextual object.
	Context Context
	// contains filtered or unexported fields
}

Big is a floating-point, arbitrary-precision

It is represented as a number and a scale. A scale greater than zero indicates the number of decimal digits after the radix. Otherwise, the number is multiplied by 10 to the power of the negation of the scale. More formally, 

Big = number × 10**-scale

with MinScale <= scale <= MaxScale. A Big may also be ±0, ±Infinity, or ±NaN (either quiet or signaling). Non-NaN Big values are ordered, defined as the result of x.Cmp(y).

Additionally, each Big value has a contextual object which governs arithmetic operations.

Example (ReversePolishNotationCalculator) 
ctx := Context128
const input = "15 7 1 1 + - / 3 * 2 1 1 + + - 5 * 3 / ="
var stack []*Big
Loop:
for _, tok := range strings.Split(input, " ") {
	last := len(stack) - 1
	switch tok {
	case "+":
		x := stack[last-1]
		ctx.Add(x, x, stack[last])
		stack = stack[:last]
	case "-":
		x := stack[last-1]
		ctx.Sub(x, x, stack[last])
		stack = stack[:last]
	case "/":
		x := stack[last-1]
		ctx.Quo(x, x, stack[last])
		stack = stack[:last]
	case "*":
		x := stack[last-1]
		ctx.Mul(x, x, stack[last])
		stack = stack[:last]
	case "=":
		break Loop
	default:
		var x Big
		if _, ok := x.SetString(tok); !ok {
			fmt.Fprintf(os.Stderr, "invalid decimal: %v\n", x.Context.Err())
			os.Exit(1)
		}
		stack = append(stack, &x)
	}
}
fmt.Printf("%+6.4g\n", stack[0])

Output:

+8.333

func BinarySplit 

func BinarySplit(z *Big, ctx Context, start, stop uint64, A, P, B, Q SplitFunc) *Big

BinarySplit sets z to the result of the binary splitting formula and returns z. The formula is defined as: 

    ∞    a(n)p(0) ... p(n)
S = Σ   -------------------
    n=0  b(n)q(0) ... q(n)

It should only be used when the number of terms is known ahead of time. If start is not in [start, stop) or stop is not in (start, stop], BinarySplit will panic.

func BinarySplitDynamic 

func BinarySplitDynamic(ctx Context, A, P, B, Q SplitFunc) *Big

BinarySplitDynamic sets z to the result of the binary splitting formula. It should be used when the number of terms is not known ahead of time. For more information, See BinarySplit.

func Max 

func Max(a, b *Big) *Big

Max returns the greater of the provided values.

The result is undefined if no values are are provided.

func MaxAbs 

func MaxAbs(x ...*Big) *Big

MaxAbs returns the greater of the absolute value of the provided values.

The result is undefined if no values are provided.

func Min 

func Min(x ...*Big) *Big

Min returns the lesser of the provided values.

The result is undefined if no values are are provided.

func MinAbs 

func MinAbs(x ...*Big) *Big

MinAbs returns the lesser of the absolute value of the provided values.

The result is undefined if no values are provided.

func New 

func New(value int64, scale int) *Big

New creates a new Big decimal with the given value and scale.

For example: 

New(1234, 3) // 1.234
New(42, 0)   // 42
New(4321, 5) // 0.04321
New(-1, 0)   // -1
New(3, -10)  // 30 000 000 000

func WithContext 

func WithContext(c Context) *Big

WithContext is shorthand to create a Big decimal from a Context.

func WithPrecision 

func WithPrecision(p int) *Big

WithPrecision is shorthand to create a Big decimal with a given precision.

func (*Big) Abs 

func (z *Big) Abs(x *Big) *Big

Abs sets z to the absolute value of x and returns z.

func (*Big) Add 

func (z *Big) Add(x, y *Big) *Big

Add sets z to x + y and returns z.

func (*Big) Canonical 

func (z *Big) Canonical(x *Big) *Big

Canonical sets z to the canonical form of z.

Since Big values are always canonical, it's identical to Copy.

func (*Big) CheckNaNs 

func (z *Big) CheckNaNs(x, y *Big) bool

CheckNaNs checks if either x or y is NaN.

If so, it follows the rules of NaN handling set forth in the GDA specification. The argument y may be nil. It reports whether either condition is a NaN.

func (*Big) Class 

func (x *Big) Class() string

Class returns the "class" of x, which is one of the following: 

sNaN
NaN
-Infinity
-Normal
-Subnormal
-Zero
+Zero
+Subnormal
+Normal
+Infinity

func (*Big) Cmp 

func (x *Big) Cmp(y *Big) int

Cmp compares x and y and returns: 

-1 if x <  y
 0 if x == y
+1 if x >  y

It does not modify x or y. The result is undefined if either x or y are NaN.

For an abstract comparison with NaN values, see CmpTotal.

func (*Big) CmpAbs 

func (x *Big) CmpAbs(y *Big) int

CmpAbs compares |x| and |y| and returns: 

-1 if |x| <  |y|
 0 if |x| == |y|
+1 if |x| >  |y|

It does not modify x or y. The result is undefined if either x or y are NaN.

For an abstract comparison with NaN values, see CmpTotalAbs.

func (*Big) CmpTotal 

func (x *Big) CmpTotal(y *Big) int

CmpTotal compares x and y in a manner similar to the Big.Cmp, but allows ordering of all abstract representations.

In particular, this means NaN values have a defined ordering. From lowest to highest the ordering is: 

-NaN
-sNaN
-Infinity
-127
-1.00
-1
-0.000
-0
+0
+1.2300
+1.23
+1E+9
+Infinity
+sNaN
+NaN

func (*Big) CmpTotalAbs 

func (x *Big) CmpTotalAbs(y *Big) int

CmpTotalAbs is like CmpTotal but instead compares the absolute values of x and y.

func (*Big) Compose 

func (z *Big) Compose(form byte, negative bool, coefficient []byte, exponent int32) error

Compose sets the internal decimal value from parts. If the value cannot be represented then an error should be returned.

func (*Big) Copy 

func (z *Big) Copy(x *Big) *Big

Copy sets z to a copy of x and returns z.

func (*Big) CopyAbs 

func (z *Big) CopyAbs(x *Big) *Big

CopyAbs is like Abs, but no flags are changed and the result is not rounded.

func (*Big) CopyNeg 

func (z *Big) CopyNeg(x *Big) *Big

CopyNeg is like Neg, but no flags are changed and the result is not rounded.

func (*Big) CopySign 

func (z *Big) CopySign(x, y *Big) *Big

CopySign sets z to x with the sign of y and returns z.

It accepts NaN values.

func (*Big) Decompose 

func (z *Big) Decompose(buf []byte) (form byte, negative bool, coefficient []byte, exponent int32)

Decompose returns the internal decimal state into parts. If the provided buf has sufficient capacity, buf may be returned as the coefficient with the value set and length set as appropriate.

func (*Big) FMA 

func (z *Big) FMA(x, y, u *Big) *Big

FMA sets z to (x * y) + u without any intermediate rounding.

func (*Big) Float 

func (x *Big) Float(z *big.Float) *big.Float

Float sets z, which may be nil, to x and returns z.

The result is undefined if z is a NaN value.

func (*Big) Float64 

func (x *Big) Float64() (f float64, ok bool)

Float64 returns x as a float64 and a bool indicating whether x can fit into a float64 without truncation, overflow, or underflow.

Special values are considered exact; however, special values that occur because the magnitude of x is too large to be represented as a float64 are not.

func (*Big) Format 

func (x *Big) Format(s fmt.State, c rune)

Format implements the fmt.Formatter interface.

The following verbs are supported: 

%s: -dddd.dd or -d.dddd±edd, depending on x
%d: same as %s
%v: same as %s
%e: -d.dddd±edd
%E: -d.dddd±Edd
%f: -dddd.dd
%g: same as %f

While width is honored in the same manner as the fmt package (the minimum width of the formatted number), precision is the number of significant digits in the decimal number. Given %f, however, precision is the number of digits following the radix.

Format honors all flags (such as '+' and ' ') in the same manner as the fmt package, except for '#'. Unless used in conjunction with %v, %q, or %p, the '#' flag will be ignored; decimals have no defined hexadeximal or octal representation.

%+v, %#v, %T, %#p, and %p all honor the formats specified in the fmt package's documentation.

Example 
print := func(format, xs string) {
	x, _ := new(Big).SetString(xs)
	fmt.Printf(format+"\n", x)
}

print("%s", "12.34")
print("%.3g", "12.34")
print("%.1f", "12.34")
print("`%6.4g`", "500.44")
print("'%-10.f'", "-404.040")

Output:

12.34
12.3
12.3
` 500.4`
'-404      '

func (*Big) Int 

func (x *Big) Int(z *big.Int) *big.Int

Int sets z, which may be nil, to x, truncating the fractional portion (if any) and returns z.

If x is an infinity or a NaN value the result is undefined.

func (*Big) Int64 

func (x *Big) Int64() (int64, bool)

Int64 returns x as an int64, truncating towards zero.

The bool result indicates whether the conversion to an int64 was successful.

func (*Big) IsFinite 

func (x *Big) IsFinite() bool

IsFinite reports whether x is finite.

func (*Big) IsInf 

func (x *Big) IsInf(sign int) bool

IsInf reports whether x is an infinity according to sign. If sign > 0, IsInf reports whether x is positive infinity. If sign < 0, IsInf reports whether x is negative infinity. If sign == 0, IsInf reports whether x is either infinity.

func (*Big) IsInt 

func (x *Big) IsInt() bool

IsInt reports whether x is an integer.

Infinity and NaN values are not integers.

func (*Big) IsNaN 

func (x *Big) IsNaN(quiet int) bool

IsNaN reports whether x is NaN. If sign > 0, IsNaN reports whether x is quiet NaN. If sign < 0, IsNaN reports whether x is signaling NaN. If sign == 0, IsNaN reports whether x is either NaN.

func (*Big) IsNormal 

func (x *Big) IsNormal() bool

IsNormal reports whether x is normal.

func (*Big) IsSubnormal 

func (x *Big) IsSubnormal() bool

IsSubnormal reports whether x is subnormal.

func (*Big) Mantissa 

func (x *Big) Mantissa() (uint64, bool)

Mantissa returns the mantissa of x and reports whether the mantissa fits into a uint64 and x is finite.

This may be used to convert a decimal representing a monetary value to its most basic unit (e.g., $123.45 to 12345 cents).

func (*Big) MarshalText 

func (x *Big) MarshalText() ([]byte, error)

MarshalText implements encoding.TextMarshaler.

func (*Big) Mul 

func (z *Big) Mul(x, y *Big) *Big

Mul sets z to x * y and returns z.

func (*Big) Neg 

func (z *Big) Neg(x *Big) *Big

Neg sets z to -x and returns z.

If x is positive infinity, z will be set to negative infinity and vice versa. If x == 0, z will be set to zero. It is an error if x is a NaN value

func (*Big) Payload 

func (x *Big) Payload() Payload

Payload returns the payload of x, provided x is a NaN value.

If x is not a NaN value, the result is undefined.

func (*Big) Precision 

func (x *Big) Precision() int

Precision returns the number of digits in the unscaled form of x.

x == 0 has a precision of 1. The result is undefined if x is not finite.

Example 
a := New(12, 0)
b := New(42, -2)
c := New(12345, 3)
d := New(3, 5)

fmt.Printf(`
%s has a precision of %d
%s has a precision of %d
%s has a precision of %d
%s has a precision of %d
`, a, a.Precision(), b, b.Precision(), c, c.Precision(), d, d.Precision())

Output:


12 has a precision of 2
4.2E+3 has a precision of 2
12.345 has a precision of 5
0.00003 has a precision of 1

func (*Big) Quantize 

func (z *Big) Quantize(n int) *Big

Quantize sets z to the number equal in value and sign to z with the scale, n.

z is rounded according to z.Context.RoundingMode. To perform truncation, set z.Context.RoundingMode to ToZero.

Example 
a, _ := WithContext(Context32).SetString("2.17")
b, _ := WithContext(Context64).SetString("217")
c, _ := WithContext(Context128).SetString("-0.1")
d, _ := WithContext(Context{OperatingMode: GDA}).SetString("-0")

fmt.Printf("A: %s\n", a.Quantize(3)) // 3 digits after radix
fmt.Printf("B: %s\n", b.Quantize(-2))
fmt.Printf("C: %s\n", c.Quantize(1))
fmt.Printf("D: %s\n", d.Quantize(-5))

Output:

A: 2.170
B: 2E+2
C: -0.1
D: -0E+5

func (*Big) Quo 

func (z *Big) Quo(x, y *Big) *Big

Quo sets z to x / y and returns z.

func (*Big) QuoInt 

func (z *Big) QuoInt(x, y *Big) *Big

QuoInt sets z to x / y with the remainder truncated. See QuoRem for more details.

func (*Big) QuoRem 

func (z *Big) QuoRem(x, y, r *Big) (*Big, *Big)

QuoRem sets z to the quotient x / y and r to the remainder x % y, such that x = z * y + r, and returns the pair (z, r).

func (*Big) Rat 

func (x *Big) Rat(z *big.Rat) *big.Rat

Rat sets z, which may be nil, to x and returns z.

The result is undefined if x is an infinity or NaN value.

func (*Big) Reduce 

func (z *Big) Reduce() *Big

Reduce reduces a finite z to its most simplest form.

func (*Big) Rem 

func (z *Big) Rem(x, y *Big) *Big

Rem sets z to the remainder x % y. See QuoRem for more details.

func (*Big) Round 

func (z *Big) Round(n int) *Big

Round rounds z down to n digits of precision and returns z.

The result is undefined if z is not finite. No rounding will occur if n <= 0. The result of Round will always be in the interval [⌊10**p⌋, z] where p = the precision of z.

Example 
a, _ := new(Big).SetString("1234")
b, _ := new(Big).SetString("54.4")
c, _ := new(Big).SetString("60")
d, _ := new(Big).SetString("0.0022")

fmt.Println(a.Round(2))
fmt.Println(b.Round(2))
fmt.Println(c.Round(5))
fmt.Println(d.Round(1))

Output:

1.2E+3
54
60
0.002

func (*Big) RoundToInt 

func (z *Big) RoundToInt() *Big

RoundToInt rounds z down to an integral value.

func (*Big) SameQuantum 

func (x *Big) SameQuantum(y *Big) bool

SameQuantum reports whether x and y have the same exponent (scale).

func (*Big) Scale 

func (x *Big) Scale() int

Scale returns x's scale.

func (*Big) Scan 

func (z *Big) Scan(state fmt.ScanState, verb rune) error

Scan implements fmt.Scanner.

func (*Big) Set 

func (z *Big) Set(x *Big) *Big

Set sets z to x and returns z.

The result might be rounded depending on z.Context, even if z == x.

func (*Big) SetBigMantScale 

func (z *Big) SetBigMantScale(value *big.Int, scale int) *Big

SetBigMantScale sets z to the given value and scale.

func (*Big) SetFloat 

func (z *Big) SetFloat(x *big.Float) *Big

SetFloat sets z to exactly x and returns z.

func (*Big) SetFloat64 

func (z *Big) SetFloat64(x float64) *Big

SetFloat64 sets z to exactly x.

func (*Big) SetInf 

func (z *Big) SetInf(signbit bool) *Big

SetInf sets z to -Inf if signbit is set or +Inf is signbit is not set, and returns z.

func (*Big) SetMantScale 

func (z *Big) SetMantScale(value int64, scale int) *Big

SetMantScale sets z to the given value and scale.

func (*Big) SetNaN 

func (z *Big) SetNaN(signal bool) *Big

SetNaN sets z to a signaling NaN if signal is true or quiet NaN otherwise and returns z.

No conditions are raised.

func (*Big) SetRat 

func (z *Big) SetRat(x *big.Rat) *Big

SetRat sets z to to the possibly rounded value of x and returns z.

func (*Big) SetScale 

func (z *Big) SetScale(scale int) *Big

SetScale sets z's scale to scale and returns z.

func (*Big) SetSignbit 

func (z *Big) SetSignbit(sign bool) *Big

SetSignbit sets z to -z if sign is true, otherwise to +z.

func (*Big) SetString 

func (z *Big) SetString(s string) (*Big, bool)

SetString sets z to the value of s and returns z.

s must have one of the following formats: 

1.234
1234
1.234e+5
1.234E-5
0.000001234
Inf
NaN
qNaN
sNaN

Each format may be preceded by an optional sign, either "-" or "+". By default, "Inf" and "NaN" map to "+Inf" and "qNaN", respectively. NaN values may have optional diagnostic information, represented as trailing digits; for example, "NaN123".

If s does not match one of the allowed formats, the ConversionSyntax condition is set.

SetString will only return (nil, false) if a library error occurs. In general, it safe to ignore the bool result.

func (*Big) SetUint64 

func (z *Big) SetUint64(x uint64) *Big

SetUint64 is shorthand for SetMantScale(x, 0) for an unsigned integer.

func (*Big) Sign 

func (x *Big) Sign() int

Sign returns: 

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

No distinction is made between +0 and -0. The result is undefined if x is a NaN value.

func (*Big) Signbit 

func (x *Big) Signbit() bool

Signbit reports whether x is negative, negative zero, negative infinity, or negative NaN.

func (*Big) String 

func (x *Big) String() string

String returns the string representation of x.

It's equivalent to the %s verb discussed in the Format method's documentation.

Special cases depend on the OperatingMode.

func (*Big) Sub 

func (z *Big) Sub(x, y *Big) *Big

Sub sets z to x - y and returns z.

func (*Big) Uint64 

func (x *Big) Uint64() (uint64, bool)

Uint64 returns x as a uint64, truncating towards zero.

The bool result indicates whether the conversion to a uint64 was successful.

func (*Big) UnmarshalJSON 

func (z *Big) UnmarshalJSON(data []byte) error

UnmarshalJSON implements json.Unmarshaler.

func (*Big) UnmarshalText 

func (z *Big) UnmarshalText(data []byte) error

UnmarshalText implements encoding.TextUnmarshaler.

type Condition 

type Condition uint32

Condition is a bitmask value raised after or during specific operations. For example, dividing by zero is undefined so a DivisionByZero Condition flag will be set in the decimal's Context. 

const (
	// Clamped occurs if the scale has been modified to fit the constraints of
	// the decimal representation.
	Clamped Condition = 1 << iota
	// ConversionSyntax occurs when a string is converted to a decimal and does
	// not have a valid syntax.
	ConversionSyntax
	// DivisionByZero occurs when division is attempted with a finite,
	// non-zero dividend and a divisor with a value of zero.
	DivisionByZero
	// DivisionImpossible occurs when the result of integer division would
	// contain too many digits (i.e. be longer than the specified precision).
	DivisionImpossible
	// DivisionUndefined occurs when division is attempted with in which both
	// the divided and divisor are zero.
	DivisionUndefined
	// Inexact occurs when the result of an operation (e.g. division) is not
	// exact, or when the Overflow/Underflow Conditions occur.
	Inexact
	// InsufficientStorage occurs when the system doesn't have enough storage
	// (i.e. memory) to store the
	InsufficientStorage
	// InvalidContext occurs when an invalid context was detected during an
	// operation. This might occur if, for example, an invalid RoundingMode was
	// passed to a Context.
	InvalidContext
	// InvalidOperation occurs when:
	//
	// 	- an operand to an operation is a signaling NaN
	// 	- an attempt is made to add or subtract infinities of opposite signs
	// 	- an attempt is made to multiply zero by an infinity of either sign
	// 	- an attempt is made to divide an infinity by an infinity
	// 	- the divisor for a remainder operation is zero
	// 	- the dividend for a remainder operation is an infinity
	// 	- either operand of the quantize operation is an infinity, or the result
	// 	  of a quantize operation would require greater precision than is
	// 	  available
	// 	- the operand of the ln or the log10 operation is less than zero
	// 	- the operand of the square-root operation has a sign of 1 and a
	// 	  non-zero coefficient
	// 	- both operands of the power operation are zero, or if the left-hand
	// 	  operand is less than zero and the right-hand operand does not have an
	// 	  integral value or is an infinity
	//
	InvalidOperation
	// Overflow occurs when the adjusted scale, after rounding, would be
	// greater than MaxScale. (Inexact and Rounded will also be raised.)
	Overflow
	// Rounded occurs when the result of an operation is rounded, or if an
	// Overflow/Underflow occurs.
	Rounded
	// Subnormal ocurs when the result of a conversion or operation is subnormal
	// (i.e. the adjusted scale is less than MinScale before any rounding).
	Subnormal
	// Underflow occurs when the result is inexact and the adjusted scale would
	// be smaller (more negative) than MinScale.
	Underflow
)

func (Condition) Error 

func (c Condition) Error() string

func (Condition) String 

func (c Condition) String() string

type Context 

type Context struct {
	// MaxScale overrides the MaxScale constant so long as it's
	// in the range (0, MaxScale].
	MaxScale int

	// MinScale overrides the MaxScale constant so long as it's
	// in the range [MinScale, 0).
	MinScale int

	// Precision is the Context's precision; that is, the maximum
	// number of significant digits that may result from any
	// arithmetic operation.  Excluding any package-defined
	// constants (e.g., "UnlimitedPrecision"), if precision is
	// not in the range [1, MaxPrecision] operations might result
	// in an error. A precision of 0 will be interpreted as
	// DefaultPrecision. For example,
	//
	//   precision ==  4 // 4
	//   precision == -4 // error
	//   precision ==  0 // DefaultPrecision
	//   precision == 12 // 12
	//
	Precision int

	// Traps are a set of exceptional conditions that should
	// result in an error.
	Traps Condition

	// Conditions are a set of the most recent exceptional
	// conditions to occur during an operation.
	Conditions Condition

	// RoundingMode determines how a decimal is rounded.
	RoundingMode RoundingMode

	// OperatingMode which dictates how the decimal operates under certain
	// conditions. See OperatingMode for more information.
	OperatingMode OperatingMode
}

Context is a per-decimal contextual object that governs specific operations.

func (Context) Abs 

func (c Context) Abs(z, x *Big) *Big

Abs sets z to the absolute value of x and returns z.

func (Context) Acos 

func (c Context) Acos(z, x *Big) *Big

Acos returns the arccosine, in radians, of x.

Range: 

Input: -1 <= x <= 1
Output: 0 <= Acos(x) <= pi

Special cases: 

Acos(NaN)  = NaN
Acos(±Inf) = NaN
Acos(x)    = NaN if x < -1 or x > 1
Acos(-1)   = pi
Acos(1)    = 0

func (Context) Add 

func (c Context) Add(z, x, y *Big) *Big

Add sets z to x + y and returns z.

func (Context) Asin 

func (c Context) Asin(z, x *Big) *Big

Asin returns the arcsine, in radians, of x.

Range: 

Input: -1 <= x <= 1
Output: -pi/2 <= Asin(x) <= pi/2

Special cases: 

Asin(NaN)  = NaN
Asin(±Inf) = NaN
Asin(x)    = NaN if x < -1 or x > 1
Asin(±1)   = ±pi/2

func (Context) Atan 

func (c Context) Atan(z, x *Big) *Big

Atan returns the arctangent, in radians, of x.

Range: 

Input: all real numbers
Output: -pi/2 <= Atan(x) <= pi/2

Special cases: 

Atan(NaN)  = NaN
Atan(±Inf) = ±x * pi/2

func (Context) Atan2 

func (c Context) Atan2(z, y, x *Big) *Big

Atan2 calculates arctan of y/x and uses the signs of y and x to determine the valid quadrant

Range: 

y input: all real numbers
x input: all real numbers
Output: -pi < Atan2(y, x) <= pi

Special cases: 

Atan2(NaN, NaN)      = NaN
Atan2(y, NaN)        = NaN
Atan2(NaN, x)        = NaN
Atan2(±0, x >=0)     = ±0
Atan2(±0, x <= -0)   = ±pi
Atan2(y > 0, 0)      = +pi/2
Atan2(y < 0, 0)      = -pi/2
Atan2(±Inf, +Inf)    = ±pi/4
Atan2(±Inf, -Inf)    = ±3pi/4
Atan2(y, +Inf)       = 0
Atan2(y > 0, -Inf)   = +pi
Atan2(y < 0, -Inf)   = -pi
Atan2(±Inf, x)       = ±pi/2
Atan2(y, x > 0)      = Atan(y/x)
Atan2(y >= 0, x < 0) = Atan(y/x) + pi
Atan2(y < 0, x < 0)  = Atan(y/x) - pi

func (Context) Ceil 

func (c Context) Ceil(z, x *Big) *Big

Ceil sets z to the least integer value greater than or equal to x and returns z.

func (Context) Cos 

func (c Context) Cos(z, x *Big) *Big

Cos returns the cosine, in radians, of x.

Range: 

Input: all real numbers
Output: -1 <= Cos(x) <= 1

Special cases: 

Cos(NaN)  = NaN
Cos(±Inf) = NaN

func (Context) E 

func (c Context) E(z *Big) *Big

E sets z to the mathematical constant e and returns z.

func (Context) Err 

func (c Context) Err() error

Err returns non-nil if there are any trapped exceptional conditions.

func (Context) Exp 

func (c Context) Exp(z, x *Big) *Big

Exp sets z to e**x and returns z.

func (Context) FMA 

func (c Context) FMA(z, x, y, u *Big) *Big

FMA sets z to (x * y) + u without any intermediate rounding.

func (Context) Floor 

func (c Context) Floor(z, x *Big) *Big

Floor sets z to the greatest integer value less than or equal to x and returns z.

func (Context) Hypot 

func (c Context) Hypot(z, p, q *Big) *Big

Hypot sets z to Sqrt(p*p + q*q) and returns z.

func (Context) Lentz 

func (c Context) Lentz(z *Big, g Generator) *Big

Lentz sets z to the result of the continued fraction provided by the Generator and returns z.

The continued fraction should be represented as such: 

                     a1
f(x) = b0 + --------------------
                       a2
            b1 + ---------------
                          a3
                 b2 + ----------
                            a4
                      b3 + -----
                             ...

Or, equivalently: 

             a1   a2   a3
f(x) = b0 + ---- ---- ----
             b1 + b2 + b3 + ···

If terms need to be subtracted, the a_N terms should be negative. To compute a continued fraction without b_0, divide the result by a_1.

If the first call to the Generator's Next method returns false, the result of Lentz is undefined.

Note: the accuracy of the result may be affected by the precision of intermediate results. If larger precision is desired, it may be necessary for the Generator to implement the Lentzer interface and set a higher precision for f, Δ, C, and D.

Example (Phi)

This example demonstrates using Lentz by calculating the golden ratio, φ. 

package main

import (
	"fmt"
	"math"
)

type phiGenerator struct {
	ctx Context
}

func (p phiGenerator) Context() Context {
	return p.ctx
}

func (phiGenerator) Next() bool {
	return true
}

func (phiGenerator) Term() Term {
	return Term{A: New(1, 0), B: New(1, 0)}
}

func (p phiGenerator) Lentz() (f, Δ, C, D, eps *Big) {
	// Add a little extra precision to C and D so we get an "exact" result after
	// rounding.
	f = WithContext(p.ctx)
	Δ = WithContext(p.ctx)
	C = WithContext(p.ctx)
	D = WithContext(p.ctx)
	scale := p.ctx.Precision
	if scale == 0 {
		scale = DefaultPrecision
	}
	eps = New(1, scale)
	return f, Δ, C, D, eps
}

// Phi sets z to the golden ratio, φ, and returns z.
func Phi(ctx Context, z *Big) *Big {
	ctx.Precision++
	ctx.Wallis(z, phiGenerator{ctx: ctx})
	ctx.Precision--
	return ctx.Round(z)
}

// This example demonstrates using Lentz by calculating the
// golden ratio, φ.
func main() {
	ctx := Context64
	var z Big
	Phi(ctx, &z)
	p := (1 + math.Sqrt(5)) / 2

	fmt.Printf(`
Go     : %g
Decimal: %s`, p, &z)
}

Output:


Go     : 1.618033988749895
Decimal: 1.618033988749895
Example (Tan) 
package main

import (
	"fmt"
)

type tanGenerator struct {
	ctx Context
	k   uint64
	a   *Big
	b   *Big
}

func (t tanGenerator) Next() bool {
	return true
}

func (t *tanGenerator) Term() Term {
	t.k += 2
	return Term{A: t.a, B: t.b.SetUint64(t.k)}
}

func (t *tanGenerator) Context() Context { return t.ctx }

// Tan sets z to the tangent of the radian argument x.
func Tan(ctx Context, z, x *Big) *Big {
	// Handle special cases like 0, Inf, and NaN.

	// In the continued fraction
	//
	//                z    z^2   z^2   z^2
	//     tan(z) = ----- ----- ----- -----
	//                1  -  3  -  5  -  7  - ···
	//
	// the terms are subtracted, so we need to negate "A"

	work := ctx
	if work.Precision == 0 {
		work.Precision = DefaultPrecision
	}
	work.Precision++

	x0 := work.Mul(new(Big), x, x)
	x0.Neg(x0)

	g := &tanGenerator{
		ctx: ctx,
		k:   1<<64 - 1,
		a:   x0,
		b:   new(Big),
	}

	// Since our fraction doesn't have a leading (b0), we need to
	// divide our result by a1.
	tan := work.Quo(z, x, work.Lentz(z, g))

	return ctx.Set(z, tan)
}

func main() {
	var z Big
	ctx := Context{Precision: 17}
	x := New(42, 0)

	fmt.Printf("tan(42) = %s\n", Tan(ctx, &z, x).Round(16))
}

Output:

tan(42) = 2.291387992437486

func (Context) Log 

func (c Context) Log(z, x *Big) *Big

Log sets z to the natural logarithm of x and returns z.

func (Context) Log10 

func (c Context) Log10(z, x *Big) *Big

Log10 sets z to the common logarithm of x and returns z.

func (Context) Mul 

func (c Context) Mul(z, x, y *Big) *Big

Mul sets z to x * y and returns z.

func (Context) Neg 

func (c Context) Neg(z, x *Big) *Big

Neg sets z to -x and returns z.

If x is positive infinity, z will be set to negative infinity and vice versa. If x == 0, z will be set to zero. It is an error if x is a NaN value

func (Context) NextMinus 

func (c Context) NextMinus(z, x *Big) *Big

NextMinus sets z to the smallest representable number that's smaller than x and returns z.

If x is negative infinity the result will be negative infinity. If the result is zero its sign will be negative and its scale will be MinScale.

func (Context) NextPlus 

func (c Context) NextPlus(z, x *Big) *Big

NextPlus sets z to the largest representable number that's larger than x and returns z.

If x is positive infinity the result will be positive infinity. If the result is zero it will be positive and its scale will be MaxScale.

func (Context) Pi 

func (c Context) Pi(z *Big) *Big

Pi sets z to the mathematical constant pi and returns z.

func (Context) Pow 

func (c Context) Pow(z, x, y *Big) *Big

Pow sets z to x**y and returns z.

func (Context) Quantize 

func (c Context) Quantize(z *Big, n int) *Big

Quantize sets z to the number equal in value and sign to z with the scale, n.

In order to perform truncation, set the Context's RoundingMode to ToZero.

func (Context) Quo 

func (c Context) Quo(z, x, y *Big) *Big

Quo sets z to x / y and returns z.

func (Context) QuoInt 

func (c Context) QuoInt(z, x, y *Big) *Big

QuoInt sets z to x / y with the remainder truncated. See QuoRem for more details.

func (Context) QuoRem 

func (c Context) QuoRem(z, x, y, r *Big) (*Big, *Big)

QuoRem sets z to the quotient x / y and r to the remainder x % y, such that x = z * y + r, and returns the pair (z, r).

func (Context) Reduce 

func (c Context) Reduce(z *Big) *Big

Reduce reduces a finite z to its most simplest form.

func (Context) Rem 

func (c Context) Rem(z, x, y *Big) *Big

Rem sets z to the remainder x % y.

See QuoRem for more details.

func (Context) Round 

func (c Context) Round(z *Big) *Big

Round rounds z down to the Context's precision and returns z.

For a finite z, result of Round will always be within the interval [⌊10**p⌋, z] where p = the precision of z. The result is undefined if z is not finite.

func (Context) RoundToInt 

func (c Context) RoundToInt(z *Big) *Big

RoundToInt rounds z down to an integral value.

func (Context) Set 

func (c Context) Set(z, x *Big) *Big

Set sets z to x and returns z.

The result might be rounded, even if z == x.

func (Context) SetRat 

func (c Context) SetRat(z *Big, x *big.Rat) *Big

SetRat sets z to to the possibly rounded value of x and returns z.

func (Context) SetString 

func (c Context) SetString(z *Big, s string) (*Big, bool)

SetString sets z to the value of s, returning z and a bool indicating success.

See Big.SetString for valid formats.

func (Context) Sin 

func (c Context) Sin(z, x *Big) *Big

Sin returns the sine, in radians, of x.

Range: 

Input: all real numbers
Output: -1 <= Sin(x) <= 1

Special cases: 

Sin(NaN) = NaN
Sin(Inf) = NaN

func (Context) Sqrt 

func (c Context) Sqrt(z, x *Big) *Big

Sqrt sets z to the square root of x and returns z.

func (Context) Sub 

func (c Context) Sub(z, x, y *Big) *Big

Sub sets z to x - y and returns z.

func (Context) Tan 

func (c Context) Tan(z, x *Big) *Big

Tan returns the tangent, in radians, of x.

Range: 

Input: -pi/2 <= x <= pi/2
Output: all real numbers

Special cases: 

Tan(NaN) = NaN
Tan(±Inf) = NaN

func (Context) Wallis 

func (c Context) Wallis(z *Big, g Generator) *Big

Wallis sets z to the result of the continued fraction provided by the Generator and returns z.

The fraction is evaluated in a top-down manner, using the recurrence algorithm discovered by John Wallis. For more information on continued fraction representations, see the Lentz function.

type Contexter 

type Contexter interface {
	Context() Context
}

Contexter allows Generators to provide a different Context than z's. It's intended to be analogous to the relationship between, for example, Context.Mul and Big.Mul.

type ErrNaN 

type ErrNaN struct {
	Msg string
}

An ErrNaN is used when a decimal operation would lead to a NaN under IEEE-754 rules. An ErrNaN implements the error interface.

func (ErrNaN) Error 

func (e ErrNaN) Error() string

type Generator 

type Generator interface {
	// Next returns true if there are future terms. Every call to Term—even the
	// first—must be preceded by a call to Next. In general, Generators should
	// always return true unless an exceptional condition occurs.
	Next() bool

	// Term returns the next term in the fraction. The caller must not modify
	// any of the Term's fields.
	Term() Term
}

Generator represents a continued fraction.

type Lentzer 

type Lentzer interface {
	// Lentz provides the backing storage for a Generator passed to the Lentz
	// function.
	//
	// In Contexter isn't implemented, f, Δ, C, and D should have large enough
	// precision to provide a correct result, (See note for the Lentz function.)
	//
	// eps should be a sufficiently small decimal, likely 1e-15 or smaller.
	//
	// For more information, refer to "Numerical Recipes in C: The Art of
	// Scientific Computing" (ISBN 0-521-43105-5), pg 171.
	Lentz() (f, Δ, C, D, eps *Big)
}

Lentzer, if implemented, allows Generators to provide their own backing storage for the Lentz function.

type OperatingMode 

type OperatingMode uint8

OperatingMode dictates how the decimal approaches specific non-numeric operations like conversions to strings and panicking on NaNs. 

const (
	// GDA strictly adheres to the General Decimal Arithmetic Specification
	// Version 1.70. In particular:
	//
	//  - at does not panic
	//  - all arithmetic operations will be rounded down to the proper precision
	//    if necessary
	//  - it utilizes traps to set both Context.Err and Context.Conditions
	//  - its string forms of qNaN, sNaN, +Inf, and -Inf are "NaN", "sNaN",
	//    "Infinity", and "-Infinity", respectively
	//
	GDA OperatingMode = iota
	// Go adheres to typical Go idioms. In particular:
	//
	//  - it panics on NaN values
	//  - has lossless (i.e., without rounding) addition, subtraction, and
	//    multiplication
	//  - traps are ignored; it does not set Context.Err or Context.Conditions
	//  - its string forms of qNaN, sNaN, +Inf, and -Inf are "NaN", "NaN",
	//     "+Inf", and "-Inf", respectively
	//
	Go
)

func (OperatingMode) String 

func (i OperatingMode) String() string

type Payload 

type Payload uint64

Payload is a NaN value's payload.

func (Payload) String 

func (i Payload) String() string

type RoundingMode 

type RoundingMode uint8

RoundingMode determines how a decimal will be rounded. 

const (
	ToNearestEven       RoundingMode = iota // == IEEE 754-2008 roundTiesToEven
	ToNearestAway                           // == IEEE 754-2008 roundTiesToAway
	ToZero                                  // == IEEE 754-2008 roundTowardZero
	AwayFromZero                            // no IEEE 754-2008 equivalent
	ToNegativeInf                           // == IEEE 754-2008 roundTowardNegative
	ToPositiveInf                           // == IEEE 754-2008 roundTowardPositive
	ToNearestTowardZero                     // no IEEE 754-2008 equivalent

)

The following rounding modes are supported.

func (RoundingMode) String 

func (i RoundingMode) String() string

type SplitFunc 

type SplitFunc func(n uint64) *Big

SplitFunc returns the intermediate value for a given n. The returned decimal must not be modified by the caller and may only be valid until the next invocation of said function. This allows the implementation to conserve memory usage.

type Term 

type Term struct {
	A, B *Big
}

Term is a specific term in a continued fraction. A and B correspond with the a and b variables of the typical representation of a continued fraction. An example can be seen in the book, “Numerical Recipes in C: The Art of Scientific Computing” (ISBN 0-521-43105-5) in figure 5.2.1 on page 169.

func (Term) String 

func (t Term) String() string

type Walliser 

type Walliser interface {
	// Wallis provides the backing storage for a Generator passed to the Wallis
	// function. See the Lentzer interface for more information.
	Wallis() (a, a1, b, b1, p, eps *Big)
}

Walliser is analogous to Lentzer, except it's for the Wallis function.

Source Files

View all Source files

Directories

Path Synopsis
fuzz
SetString
internal
arith
Package arith provides performance-sensitive arithmetic operations.
 Package arith provides performance-sensitive arithmetic operations.
c
Package c provides internal constants.
 Package c provides internal constants.
Package math implements various useful mathematical functions and constants.
 Package math implements various useful mathematical functions and constants.
debug
Package debug provides simple routines for debugging continued fractions.
 Package debug provides simple routines for debugging continued fractions.
Package misc contains miscellaneous decimal routes.
 Package misc contains miscellaneous decimal routes.
sql
Package sql provides the ability to use Big decimals with SQL databases.
 Package sql provides the ability to use Big decimals with SQL databases.
postgres
Package postgres provides a simple wrapper around a decimal.Big type, allowing it to be used in PostgreSQL queries.
 Package postgres provides a simple wrapper around a decimal.Big type, allowing it to be used in PostgreSQL queries.
Package suite provides a simple API for parsing and using IBM Labs' "Floating-Point Test-Suite for IEEE"
 Package suite provides a simple API for parsing and using IBM Labs' "Floating-Point Test-Suite for IEEE"

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