Decimal v1.8.1 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

coefficient()

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

decimal()

exponent()

The exponent to which 10 is raised.

rounding()

Rounding algorithm.

sign()

1 for positive
-1 for negative

signal()

t()

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

Functions

abs(num)

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

add(num1, num2)

Adds two numbers together.

cast(float)

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

cmp(num1, num2)

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.

compare(num1, num2)

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.

decimal?(arg1)

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

div(num1, num2)

Divides two numbers.

div_int(num1, num2)

Divides two numbers and returns the integer part.

div_rem(num1, num2)

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)}.

eq?(num1, num2)

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.

equal?(num1, num2)

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

from_float(float)

Creates a new decimal number from a floating point number.

get_context()

Gets the process' context.

gt?(num1, num2)

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.

inf?(decimal)

Returns true if number is ±Infinity, otherwise false.

lt?(num1, num2)

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.

max(num1, num2)

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.

min(num1, num2)

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.

minus(num)

Negates the given number.

mult(num1, num2)

Multiplies two numbers.

nan?(decimal)

Returns true if number is NaN, otherwise false.

negative?(num)

Check if given number is negative

new(num)

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

new(sign, coef, exp)

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

parse(binary)

Parses a binary into a decimal.

plus(num)

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

positive?(num)

Check if given number is positive

reduce(num)

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

rem(num1, num2)

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

round(num, places \\ 0, mode \\ :half_up)

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_context(context)

Set the process' context.

sqrt(num)

Finds the square root.

sub(num1, num2)

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

to_float(decimal)

Returns the decimal converted to a float.

to_integer(decimal)

Returns the decimal represented as an integer.

to_string(num, type \\ :scientific)

Converts given number to its string representation.

update_context(fun)

Update the process' context.

with_context(context, fun)

Runs function with given context.

Link to this section Types

coefficient()

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.

decimal()

decimal() :: t() | integer() | String.t()

exponent()

exponent() :: integer()

The exponent to which 10 is raised.

rounding()

rounding() ::
  :down | :half_up | :half_even | :ceiling | :floor | :half_down | :up

Rounding algorithm.

See Decimal.Context for more information.

sign()

sign() :: 1 | -1

1 for positive
-1 for negative

signal()

signal() :: :invalid_operation | :division_by_zero | :rounded | :inexact

t()

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

abs(num)

abs(t()) :: t()

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

add(num1, num2)

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>

iex> Decimal.add(1, "Inf")
#Decimal<Infinity>

cast(float)

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>

cmp(num1, num2)

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

compare(num1, num2)

compare(decimal(), decimal()) :: t()

Examples

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

iex> Decimal.compare("Inf", -1)
#Decimal<1>

decimal?(arg1)

decimal?(any()) :: boolean()

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

div(num1, num2)

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>

div_int(num1, num2)

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>

div_rem(num1, num2)

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)}

eq?(num1, num2)

(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

equal?(num1, num2)

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

from_float(float)

(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>

get_context()

get_context() :: Decimal.Context.t()

Gets the process' context.

gt?(num1, num2)

(since 1.8.0)

gt?(decimal(), decimal()) :: boolean()

Examples

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

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

inf?(decimal)

inf?(t()) :: boolean()

Returns true if number is ±Infinity, otherwise false.

lt?(num1, num2)

(since 1.8.0)

lt?(decimal(), decimal()) :: boolean()

Examples

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

iex> Decimal.lt?("1.4", "1.2")
false

max(num1, num2)

max(decimal(), decimal()) :: t()

Examples

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

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

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

min(num1, num2)

min(decimal(), decimal()) :: t()

Examples

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

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

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

minus(num)

minus(decimal()) :: t()

Negates the given number.

Examples

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

iex> Decimal.minus("-Inf")
#Decimal<Infinity>

mult(num1, num2)

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>

nan?(decimal)

nan?(t()) :: boolean()

Returns true if number is NaN, otherwise false.

negative?(num)

(since 1.5.0)

negative?(t()) :: boolean()

Check if given number is negative

new(num)

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

Examples

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

iex> Decimal.new("3.14")
#Decimal<3.14>

new(sign, coef, exp)

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.

parse(binary)

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}}

iex> Decimal.parse("bad")
:error

plus(num)

plus(t()) :: t()

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

positive?(num)

(since 1.5.0)

positive?(t()) :: boolean()

Check if given number is positive

reduce(num)

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>

rem(num1, num2)

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>

round(num, places \\ 0, mode \\ :half_up)

round(decimal(), integer(), rounding()) :: t()

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>

set_context(context)

set_context(Decimal.Context.t()) :: :ok

Set the process' context.

sqrt(num)

(since 1.7.0)

sqrt(decimal()) :: t()

Finds the square root.

Examples

iex> Decimal.sqrt("100")
#Decimal<10>

sub(num1, num2)

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>

to_float(decimal)

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.

to_integer(decimal)

to_integer(t()) :: integer()

Returns the decimal represented as an integer.

Fails when loss of precision will occur.

to_string(num, type \\ :scientific)

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.

update_context(fun)

update_context((Decimal.Context.t() -> Decimal.Context.t())) :: :ok

Update the process' context.

with_context(context, fun)

with_context(Decimal.Context.t(), (() -> x)) :: x when x: var

Runs function with given context.