# Decimal v1.8.0 Decimal View Source

Decimal arithmetic on arbitrary precision floating-point numbers.

A number is represented by a signed coefficient and exponent such that: `sign * coefficient * 10 ^ exponent`. All numbers are represented and calculated exactly, but the result of an operation may be rounded depending on the context the operation is performed with, see: `Decimal.Context`. Trailing zeros in the coefficient are never truncated to preserve the number of significant digits unless explicitly done so.

There are also special values such as NaN (not a number) and ±Infinity. -0 and +0 are two distinct values. Some operation results are not defined and will return NaN. This kind of NaN is quiet, any operation returning a number will return NaN when given a quiet NaN (the NaN value will flow through all operations). The other kind of NaN is signalling which is the value that can be reached in `result` field on `Decimal.Error` when the result is NaN. Any operation given a signalling NaN return will signal `:invalid_operation`.

Exceptional conditions are grouped into signals, each signal has a flag and a trap enabler in the context. Whenever a signal is triggered it's flag is set in the context and will be set until explicitly cleared. If the signal is trap enabled `Decimal.Error` will be raised.

## Specifications

This implementation follows the above standards as closely as possible. But at some places the implementation diverges from the specification. The reasons are different for each case but may be that the specification doesn't map to this environment, ease of implementation or that API will be nicer. Still, the implementation is close enough that the specifications can be seen as additional documentation that can be used when things are unclear.

The specification models the sign of the number as 1, for a negative number, and 0 for a positive number. Internally this implementation models the sign as 1 or -1 such that the complete number will be `sign * coefficient * 10 ^ exponent` and will refer to the sign in documentation as either positive or negative.

There is currently no maximum or minimum values for the exponent. Because of that all numbers are "normal". This means that when an operation should, according to the specification, return a number that "underflow" 0 is returned instead of Etiny. This may happen when dividing a number with infinity. Additionally, overflow, underflow and clamped may never be signalled.

# Link to this section Summary

## Types

The coefficient of the power of `10`. Non-negative because the sign is stored separately in `sign`.

The exponent to which `10` is raised.

Rounding algorithm.

• `1` for positive
• `-1` for negative

This implementation models the `sign` as `1` or `-1` such that the complete number will be: `sign * coef * 10 ^ exp`.

## Functions

The absolute value of given number. Sets the number's sign to positive.

Adds two numbers together.

Creates a new decimal number from an integer, string, float, or existing decimal number.

Compares two numbers numerically. If the first number is greater than the second `:gt` is returned, if less than `:lt` is returned, if both numbers are equal `:eq` is returned.

Compares two numbers numerically. If the first number is greater than the second `#Decimal<1>` is returned, if less than `#Decimal<-1>` is returned. Otherwise, if both numbers are equal `#Decimal<0>` is returned. If either number is a quiet NaN, then that number is returned.

Returns `true` if argument is a decimal number, otherwise `false`.

Divides two numbers.

Divides two numbers and returns the integer part.

Integer division of two numbers and the remainder. Should be used when both `div_int/2` and `rem/2` is needed. Equivalent to: `{Decimal.div_int(x, y), Decimal.rem(x, y)}`.

Compares two numbers numerically and returns `true` if they are equal, otherwise `false`. If one of the operands is a quiet NaN this operation will always return `false`.

Compares two numbers numerically and returns `true` if they are equal, otherwise `false`.

Creates a new decimal number from a floating point number.

Gets the process' context.

Compares two numbers numerically and returns `true` if the the first argument is greater than the second, otherwise `false`. If one the operands is a quiet NaN this operation will always return `false`.

Returns `true` if number is ±Infinity, otherwise `false`.

Compares two numbers numerically and returns `true` if the the first number is less than the second number, otherwise `false`. If one of the operands is a quiet NaN this operation will always return `false`.

Compares two values numerically and returns the maximum. Unlike most other functions in `Decimal` if a number is NaN the result will be the other number. Only if both numbers are NaN will NaN be returned.

Compares two values numerically and returns the minimum. Unlike most other functions in `Decimal` if a number is NaN the result will be the other number. Only if both numbers are NaN will NaN be returned.

Negates the given number.

Multiplies two numbers.

Returns `true` if number is NaN, otherwise `false`.

Check if given number is negative

Creates a new decimal number from an integer or a string representation.

Creates a new decimal number from the sign, coefficient and exponent such that the number will be: `sign * coefficient * 10 ^ exponent`.

Parses a binary into a decimal.

Applies the context to the given number rounding it to specified precision.

Check if given number is positive

Reduces the given number. Removes trailing zeros from coefficient while keeping the number numerically equivalent by increasing the exponent.

Remainder of integer division of two numbers. The result will have the sign of the first number.

Rounds the given number to specified decimal places with the given strategy (default is to round to nearest one). If places is negative, at least that many digits to the left of the decimal point will be zero.

Set the process' context.

Finds the square root.

Subtracts second number from the first. Equivalent to `Decimal.add/2` when the second number's sign is negated.

Returns the decimal converted to a float.

Returns the decimal represented as an integer.

Converts given number to its string representation.

Update the process' context.

Runs function with given context.

# Link to this section Types

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# coefficient() View Source `coefficient() :: non_neg_integer() | :qNaN | :sNaN | :inf`

The coefficient of the power of `10`. Non-negative because the sign is stored separately in `sign`.

• `non_neg_integer` - when the `t` represents a number, instead of one of the special values below.
• `:qNaN` - a quiet NaN was produced by a previous operation. Quiet NaNs propagate quietly, unlike signaling NaNs that return errors (based on the `Decimal.Context`).
• `:sNaN` - signalling NaN that indicated an error occurred that should stop the next operation with an error (based on the `Decimal.Context`).
• `:inf` - Infinity.
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# decimal() View Source `decimal() :: t() | integer() | String.t()`

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# exponent() View Source `exponent() :: integer()`

The exponent to which `10` is raised.

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# rounding() View Source ```rounding() :: :down | :half_up | :half_even | :ceiling | :floor | :half_down | :up```

Rounding algorithm.

See `Decimal.Context` for more information.

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# sign() View Source `sign() :: 1 | -1`

• `1` for positive
• `-1` for negative
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# signal() View Source `signal() :: :invalid_operation | :division_by_zero | :rounded | :inexact`

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# t() View Source `t() :: %Decimal{coef: coefficient(), exp: exponent(), sign: sign()}`

This implementation models the `sign` as `1` or `-1` such that the complete number will be: `sign * coef * 10 ^ exp`.

• `coef` - the coefficient of the power of `10`.
• `exp` - the exponent of the power of `10`.
• `sign` - `1` for positive, `-1` for negative.

# Link to this section Functions

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# abs(num) View Source `abs(t()) :: t()`

The absolute value of given number. Sets the number's sign to positive.

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# add(num1, num2) View Source `add(decimal(), decimal()) :: t()`

Adds two numbers together.

## Exceptional conditions

• If one number is -Infinity and the other +Infinity `:invalid_operation` will be signalled.

## Examples

``````iex> Decimal.add(1, "1.1")
#Decimal<2.1>

#Decimal<Infinity>``````
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# cast(float) View Source `cast(float() | decimal()) :: t()`

Creates a new decimal number from an integer, string, float, or existing decimal number.

Because conversion from a floating point number is not exact, it's recommended to instead use `new/1` or `from_float/1` when the argument's type is certain. See `from_float/1`.

If the value cannot be cast, Decimal.Error is raised.

## Examples

``````iex> Decimal.cast(3)
#Decimal<3>

iex> Decimal.cast(3.0)
#Decimal<3.0>

iex> Decimal.cast("3")
#Decimal<3>

iex> Decimal.cast("3.0")
#Decimal<3.0>

iex> Decimal.new(3) |> Decimal.cast()
#Decimal<3>``````
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# cmp(num1, num2) View Source `cmp(decimal(), decimal()) :: :lt | :eq | :gt`

Compares two numbers numerically. If the first number is greater than the second `:gt` is returned, if less than `:lt` is returned, if both numbers are equal `:eq` is returned.

Neither number can be a NaN. If you need to handle quiet NaNs, use `compare/2`.

## Examples

``````iex> Decimal.cmp("1.0", 1)
:eq

iex> Decimal.cmp("Inf", -1)
:gt``````
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# compare(num1, num2) View Source `compare(decimal(), decimal()) :: t()`

Compares two numbers numerically. If the first number is greater than the second `#Decimal<1>` is returned, if less than `#Decimal<-1>` is returned. Otherwise, if both numbers are equal `#Decimal<0>` is returned. If either number is a quiet NaN, then that number is returned.

## Examples

``````iex> Decimal.compare("1.0", 1)
#Decimal<0>

iex> Decimal.compare("Inf", -1)
#Decimal<1>``````
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# decimal?(arg1) View Source `decimal?(any()) :: boolean()`

Returns `true` if argument is a decimal number, otherwise `false`.

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# div(num1, num2) View Source `div(decimal(), decimal()) :: t()`

Divides two numbers.

## Exceptional conditions

• If both numbers are ±Infinity `:invalid_operation` is signalled.
• If both numbers are ±0 `:invalid_operation` is signalled.
• If second number (denominator) is ±0 `:division_by_zero` is signalled.

## Examples

``````iex> Decimal.div(3, 4)
#Decimal<0.75>

iex> Decimal.div("Inf", -1)
#Decimal<-Infinity>``````
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# div_int(num1, num2) View Source `div_int(decimal(), decimal()) :: t()`

Divides two numbers and returns the integer part.

## Exceptional conditions

• If both numbers are ±Infinity `:invalid_operation` is signalled.
• If both numbers are ±0 `:invalid_operation` is signalled.
• If second number (denominator) is ±0 `:division_by_zero` is signalled.

## Examples

``````iex> Decimal.div_int(5, 2)
#Decimal<2>

iex> Decimal.div_int("Inf", -1)
#Decimal<-Infinity>``````
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# div_rem(num1, num2) View Source `div_rem(decimal(), decimal()) :: {t(), t()}`

Integer division of two numbers and the remainder. Should be used when both `div_int/2` and `rem/2` is needed. Equivalent to: `{Decimal.div_int(x, y), Decimal.rem(x, y)}`.

## Exceptional conditions

• If both numbers are ±Infinity `:invalid_operation` is signalled.
• If both numbers are ±0 `:invalid_operation` is signalled.
• If second number (denominator) is ±0 `:division_by_zero` is signalled.

## Examples

``````iex> Decimal.div_rem(5, 2)
{Decimal.new(2), Decimal.new(1)}``````
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# eq?(num1, num2) View Source (since 1.8.0) `eq?(decimal(), decimal()) :: boolean()`

Compares two numbers numerically and returns `true` if they are equal, otherwise `false`. If one of the operands is a quiet NaN this operation will always return `false`.

## Examples

``````iex> Decimal.eq?("1.0", 1)
true

iex> Decimal.eq?(1, -1)
false``````
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# equal?(num1, num2) View Source `equal?(decimal(), decimal()) :: boolean()`

Compares two numbers numerically and returns `true` if they are equal, otherwise `false`.

## Examples

``````iex> Decimal.equal?("1.0", 1)
true

iex> Decimal.equal?(1, -1)
false``````
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# from_float(float) View Source (since 1.5.0) `from_float(float()) :: t()`

Creates a new decimal number from a floating point number.

Floating point numbers use a fixed number of binary digits to represent a decimal number which has inherent inaccuracy as some decimal numbers cannot be represented exactly in limited precision binary.

Floating point numbers will be converted to decimal numbers with `:io_lib_format.fwrite_g/1`. Since this conversion is not exact and because of inherent inaccuracy mentioned above, we may run into counter-intuitive results:

``````iex> Enum.reduce([0.1, 0.1, 0.1], &+/2)
0.30000000000000004

iex> Enum.reduce([Decimal.new("0.1"), Decimal.new("0.1"), Decimal.new("0.1")], &Decimal.add/2)
#Decimal<0.3>``````

For this reason, it's recommended to build decimals with `new/1`, which is always precise, instead.

## Examples

``````iex> Decimal.from_float(3.14)
#Decimal<3.14>``````
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# get_context() View Source `get_context() :: Decimal.Context.t()`

Gets the process' context.

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# gt?(num1, num2) View Source (since 1.8.0) `gt?(decimal(), decimal()) :: boolean()`

Compares two numbers numerically and returns `true` if the the first argument is greater than the second, otherwise `false`. If one the operands is a quiet NaN this operation will always return `false`.

## Examples

``````iex> Decimal.gt?("1.3", "1.2")
true

iex> Decimal.gt?("1.2", "1.3")
false``````
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# inf?(decimal) View Source `inf?(t()) :: boolean()`

Returns `true` if number is ±Infinity, otherwise `false`.

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# lt?(num1, num2) View Source (since 1.8.0) `lt?(decimal(), decimal()) :: boolean()`

Compares two numbers numerically and returns `true` if the the first number is less than the second number, otherwise `false`. If one of the operands is a quiet NaN this operation will always return `false`.

## Examples

``````iex> Decimal.lt?("1.1", "1.2")
true

iex> Decimal.lt?("1.4", "1.2")
false``````
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# max(num1, num2) View Source `max(decimal(), decimal()) :: t()`

Compares two values numerically and returns the maximum. Unlike most other functions in `Decimal` if a number is NaN the result will be the other number. Only if both numbers are NaN will NaN be returned.

## Examples

``````iex> Decimal.max(1, "2.0")
#Decimal<2.0>

iex> Decimal.max(1, "NaN")
#Decimal<1>

iex> Decimal.max("NaN", "NaN")
#Decimal<NaN>``````
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# min(num1, num2) View Source `min(decimal(), decimal()) :: t()`

Compares two values numerically and returns the minimum. Unlike most other functions in `Decimal` if a number is NaN the result will be the other number. Only if both numbers are NaN will NaN be returned.

## Examples

``````iex> Decimal.min(1, "2.0")
#Decimal<1>

iex> Decimal.min(1, "NaN")
#Decimal<1>

iex> Decimal.min("NaN", "NaN")
#Decimal<NaN>``````
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# minus(num) View Source `minus(decimal()) :: t()`

Negates the given number.

## Examples

``````iex> Decimal.minus(1)
#Decimal<-1>

iex> Decimal.minus("-Inf")
#Decimal<Infinity>``````
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# mult(num1, num2) View Source `mult(decimal(), decimal()) :: t()`

Multiplies two numbers.

## Exceptional conditions

• If one number is ±0 and the other is ±Infinity `:invalid_operation` is signalled.

## Examples

``````iex> Decimal.mult("0.5", 3)
#Decimal<1.5>

iex> Decimal.mult("Inf", -1)
#Decimal<-Infinity>``````
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# nan?(decimal) View Source `nan?(t()) :: boolean()`

Returns `true` if number is NaN, otherwise `false`.

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# negative?(num) View Source (since 1.5.0) `negative?(t()) :: boolean()`

Check if given number is negative

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# new(num) View Source `new(decimal()) :: t()`

Creates a new decimal number from an integer or a string representation.

A decimal number will always be created exactly as specified with all digits kept - it will not be rounded with the context.

## Backus–Naur form

``````sign           ::=  "+" | "-"
digit          ::=  "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
indicator      ::=  "e" | "E"
digits         ::=  digit [digit]...
decimal-part   ::=  digits "." [digits] | ["."] digits
exponent-part  ::=  indicator [sign] digits
infinity       ::=  "Infinity" | "Inf"
nan            ::=  "NaN" [digits] | "sNaN" [digits]
numeric-value  ::=  decimal-part [exponent-part] | infinity
numeric-string ::=  [sign] numeric-value | [sign] nan``````

## Floats

See also `from_float/1`.

## Examples

``````iex> Decimal.new(1)
#Decimal<1>

iex> Decimal.new("3.14")
#Decimal<3.14>``````
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# new(sign, coef, exp) View Source `new(1 | -1, non_neg_integer() | :qNaN | :sNaN | :inf, integer()) :: t()`

Creates a new decimal number from the sign, coefficient and exponent such that the number will be: `sign * coefficient * 10 ^ exponent`.

A decimal number will always be created exactly as specified with all digits kept - it will not be rounded with the context.

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# parse(binary) View Source `parse(String.t()) :: {:ok, t()} | :error`

Parses a binary into a decimal.

If successful, returns a tuple in the form of `{:ok, decimal}`, otherwise `:error`.

## Examples

``````iex> Decimal.parse("3.14")
{:ok, %Decimal{coef: 314, exp: -2, sign: 1}}

iex> Decimal.parse("-1.1e3")
{:ok, %Decimal{coef: 11, exp: 2, sign: -1}}

:error``````
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# plus(num) View Source `plus(t()) :: t()`

Applies the context to the given number rounding it to specified precision.

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# positive?(num) View Source (since 1.5.0) `positive?(t()) :: boolean()`

Check if given number is positive

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# reduce(num) View Source `reduce(t()) :: t()`

Reduces the given number. Removes trailing zeros from coefficient while keeping the number numerically equivalent by increasing the exponent.

## Examples

``````iex> Decimal.reduce(Decimal.new("1.00"))
#Decimal<1>

iex> Decimal.reduce(Decimal.new("1.01"))
#Decimal<1.01>``````
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# rem(num1, num2) View Source `rem(decimal(), decimal()) :: t()`

Remainder of integer division of two numbers. The result will have the sign of the first number.

## Exceptional conditions

• If both numbers are ±Infinity `:invalid_operation` is signalled.
• If both numbers are ±0 `:invalid_operation` is signalled.
• If second number (denominator) is ±0 `:division_by_zero` is signalled.

## Examples

``````iex> Decimal.rem(5, 2)
#Decimal<1>``````
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# round(num, places \\ 0, mode \\ :half_up) View Source `round(decimal(), integer(), rounding()) :: t()`

Rounds the given number to specified decimal places with the given strategy (default is to round to nearest one). If places is negative, at least that many digits to the left of the decimal point will be zero.

See `Decimal.Context` for more information about rounding algorithms.

## Examples

``````iex> Decimal.round("1.234")
#Decimal<1>

iex> Decimal.round("1.234", 1)
#Decimal<1.2>``````
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# set_context(context) View Source `set_context(Decimal.Context.t()) :: :ok`

Set the process' context.

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# sqrt(num) View Source (since 1.7.0) `sqrt(decimal()) :: t()`

Finds the square root.

## Examples

``````iex> Decimal.sqrt("100")
#Decimal<10>``````
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# sub(num1, num2) View Source `sub(decimal(), decimal()) :: t()`

Subtracts second number from the first. Equivalent to `Decimal.add/2` when the second number's sign is negated.

## Exceptional conditions

• If one number is -Infinity and the other +Infinity `:invalid_operation` will be signalled.

## Examples

``````iex> Decimal.sub(1, "0.1")
#Decimal<0.9>

iex> Decimal.sub(1, "Inf")
#Decimal<-Infinity>``````
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# to_float(decimal) View Source `to_float(t()) :: float()`

Returns the decimal converted to a float.

The returned float may have lower precision than the decimal. Fails if the decimal cannot be converted to a float.

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# to_integer(decimal) View Source `to_integer(t()) :: integer()`

Returns the decimal represented as an integer.

Fails when loss of precision will occur.

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# to_string(num, type \\ :scientific) View Source `to_string(t(), :scientific | :normal | :xsd | :raw) :: String.t()`

Converts given number to its string representation.

## Options

• `:scientific` - number converted to scientific notation.
• `:normal` - number converted without a exponent.
• `:xsd` - number converted to the canonical XSD representation.
• `:raw` - number converted to its raw, internal format.
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# update_context(fun) View Source `update_context((Decimal.Context.t() -> Decimal.Context.t())) :: :ok`

Update the process' context.

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# with_context(context, fun) View Source `with_context(Decimal.Context.t(), (() -> x)) :: x when x: var`

Runs function with given context.