BigDecimal

Class

BigDecimal provides arbitrary-precision floating point decimal arithmetic.

Introduction

Ruby provides built-in support for arbitrary precision integer arithmetic.

For example:

42**13  #=>   1265437718438866624512

BigDecimal provides similar support for very large or very accurate floating point numbers.

Decimal arithmetic is also useful for general calculation, because it provides the correct answers people expect–whereas normal binary floating point arithmetic often introduces subtle errors because of the conversion between base 10 and base 2.

For example, try:

sum = 0
10_000.times do
  sum = sum + 0.0001
end
print sum #=> 0.9999999999999062

and contrast with the output from:

require 'bigdecimal'

sum = BigDecimal("0")
10_000.times do
  sum = sum + BigDecimal("0.0001")
end
print sum #=> 0.1E1

Similarly:

(BigDecimal("1.2") - BigDecimal("1.0")) == BigDecimal("0.2") #=> true

(1.2 - 1.0) == 0.2 #=> false

A Note About Precision

For a calculation using a BigDecimal and another value, the precision of the result depends on the type of value:

  • If value is a Float, the precision is Float::DIG + 1.

  • If value is a Rational, the precision is larger than Float::DIG + 1.

  • If value is a BigDecimal, the precision is value‘s precision in the internal representation, which is platform-dependent.

  • If value is other object, the precision is determined by the result of +BigDecimal(value)+.

Special features of accurate decimal arithmetic

Because BigDecimal is more accurate than normal binary floating point arithmetic, it requires some special values.

Infinity

BigDecimal sometimes needs to return infinity, for example if you divide a value by zero.

BigDecimal("1.0") / BigDecimal("0.0")  #=> Infinity
BigDecimal("-1.0") / BigDecimal("0.0")  #=> -Infinity

You can represent infinite numbers to BigDecimal using the strings 'Infinity', '+Infinity' and '-Infinity' (case-sensitive)

Not a Number

When a computation results in an undefined value, the special value NaN (for ‘not a number’) is returned.

Example:

BigDecimal("0.0") / BigDecimal("0.0") #=> NaN

You can also create undefined values.

NaN is never considered to be the same as any other value, even NaN itself:

n = BigDecimal('NaN')
n == 0.0 #=> false
n == n #=> false

Positive and negative zero

If a computation results in a value which is too small to be represented as a BigDecimal within the currently specified limits of precision, zero must be returned.

If the value which is too small to be represented is negative, a BigDecimal value of negative zero is returned.

BigDecimal("1.0") / BigDecimal("-Infinity") #=> -0.0

If the value is positive, a value of positive zero is returned.

BigDecimal("1.0") / BigDecimal("Infinity") #=> 0.0

(See BigDecimal.mode for how to specify limits of precision.)

Note that -0.0 and 0.0 are considered to be the same for the purposes of comparison.

Note also that in mathematics, there is no particular concept of negative or positive zero; true mathematical zero has no sign.

bigdecimal/util

When you require bigdecimal/util, the to_d method will be available on BigDecimal and the native Integer, Float, Rational, and String classes:

require 'bigdecimal/util'

42.to_d         # => 0.42e2
0.5.to_d        # => 0.5e0
(2/3r).to_d(3)  # => 0.667e0
"0.5".to_d      # => 0.5e0

License

Copyright © 2002 by Shigeo Kobayashi <shigeo@tinyforest.gr.jp>.

BigDecimal is released under the Ruby and 2-clause BSD licenses. See LICENSE.txt for details.

Maintained by mrkn <mrkn@mrkn.jp> and ruby-core members.

Documented by zzak <zachary@zacharyscott.net>, mathew <meta@pobox.com>, and many other contributors.

Constants

VERSION

The version of bigdecimal library

BASE

Base value used in internal calculations. On a 32 bit system, BASE is 10000, indicating that calculation is done in groups of 4 digits. (If it were larger, BASE**2 wouldn’t fit in 32 bits, so you couldn’t guarantee that two groups could always be multiplied together without overflow.)

EXCEPTION_ALL

Determines whether overflow, underflow or zero divide result in an exception being thrown. See BigDecimal.mode.

EXCEPTION_NaN

Determines what happens when the result of a computation is not a number (NaN). See BigDecimal.mode.

EXCEPTION_INFINITY

Determines what happens when the result of a computation is infinity. See BigDecimal.mode.

EXCEPTION_UNDERFLOW

Determines what happens when the result of a computation is an underflow (a result too small to be represented). See BigDecimal.mode.

EXCEPTION_OVERFLOW

Determines what happens when the result of a computation is an overflow (a result too large to be represented). See BigDecimal.mode.

EXCEPTION_ZERODIVIDE

Determines what happens when a division by zero is performed. See BigDecimal.mode.

ROUND_MODE

Determines what happens when a result must be rounded in order to fit in the appropriate number of significant digits. See BigDecimal.mode.

ROUND_UP

Indicates that values should be rounded away from zero. See BigDecimal.mode.

ROUND_DOWN

Indicates that values should be rounded towards zero. See BigDecimal.mode.

ROUND_HALF_UP

Indicates that digits >= 5 should be rounded up, others rounded down. See BigDecimal.mode.

ROUND_HALF_DOWN

Indicates that digits >= 6 should be rounded up, others rounded down. See BigDecimal.mode.

ROUND_CEILING

Round towards +Infinity. See BigDecimal.mode.

ROUND_FLOOR

Round towards -Infinity. See BigDecimal.mode.

ROUND_HALF_EVEN

Round towards the even neighbor. See BigDecimal.mode.

SIGN_NaN

Indicates that a value is not a number. See BigDecimal.sign.

SIGN_POSITIVE_ZERO

Indicates that a value is +0. See BigDecimal.sign.

SIGN_NEGATIVE_ZERO

Indicates that a value is -0. See BigDecimal.sign.

SIGN_POSITIVE_FINITE

Indicates that a value is positive and finite. See BigDecimal.sign.

SIGN_NEGATIVE_FINITE

Indicates that a value is negative and finite. See BigDecimal.sign.

SIGN_POSITIVE_INFINITE

Indicates that a value is positive and infinite. See BigDecimal.sign.

SIGN_NEGATIVE_INFINITE

Indicates that a value is negative and infinite. See BigDecimal.sign.

INFINITY

Special value constants

NAN

No documentation available
Class Methods

_load(p1)
::

Internal method used to provide marshalling support. See the Marshal module.

BigDecimal.double_fig → integer
::

Returns the number of digits a Float object is allowed to have; the result is system-dependent:

BigDecimal.double_fig # => 16

interpret_loosely(p1)
::
No documentation available

json_create(object)
::

Import a JSON Marshalled object.

method used for JSON marshalling support.

BigDecimal.limit(digits)
::

Limit the number of significant digits in newly created BigDecimal numbers to the specified value. Rounding is performed as necessary, as specified by BigDecimal.mode.

A limit of 0, the default, means no upper limit.

The limit specified by this method takes less priority over any limit specified to instance methods such as ceil, floor, truncate, or round.

BigDecimal.mode(mode, setting = nil) → integer
::

Returns an integer representing the mode settings for exception handling and rounding.

These modes control exception handling:

  • BigDecimal::EXCEPTION_NaN.

  • BigDecimal::EXCEPTION_INFINITY.

  • BigDecimal::EXCEPTION_UNDERFLOW.

  • BigDecimal::EXCEPTION_OVERFLOW.

  • BigDecimal::EXCEPTION_ZERODIVIDE.

  • BigDecimal::EXCEPTION_ALL.

Values for setting for exception handling:

  • true: sets the given mode to true.

  • false: sets the given mode to false.

  • nil: does not modify the mode settings.

You can use method BigDecimal.save_exception_mode to temporarily change, and then automatically restore, exception modes.

For clarity, some examples below begin by setting all exception modes to false.

This mode controls the way rounding is to be performed:

  • BigDecimal::ROUND_MODE

You can use method BigDecimal.save_rounding_mode to temporarily change, and then automatically restore, the rounding mode.

NaNs

Mode BigDecimal::EXCEPTION_NaN controls behavior when a BigDecimal NaN is created.

Settings:

Examples:

BigDecimal.mode(BigDecimal::EXCEPTION_ALL, false) # => 0
BigDecimal('NaN')                                 # => NaN
BigDecimal.mode(BigDecimal::EXCEPTION_NaN, true)  # => 2
BigDecimal('NaN') # Raises FloatDomainError

Infinities

Mode BigDecimal::EXCEPTION_INFINITY controls behavior when a BigDecimal Infinity or -Infinity is created. Settings:

  • false (default): Returns BigDecimal('Infinity') or BigDecimal('-Infinity').

  • true: Raises FloatDomainError.

Examples:

BigDecimal.mode(BigDecimal::EXCEPTION_ALL, false)     # => 0
BigDecimal('Infinity')                                # => Infinity
BigDecimal('-Infinity')                               # => -Infinity
BigDecimal.mode(BigDecimal::EXCEPTION_INFINITY, true) # => 1
BigDecimal('Infinity')  # Raises FloatDomainError
BigDecimal('-Infinity') # Raises FloatDomainError

Underflow

Mode BigDecimal::EXCEPTION_UNDERFLOW controls behavior when a BigDecimal underflow occurs. Settings:

  • false (default): Returns BigDecimal('0') or BigDecimal('-Infinity').

  • true: Raises FloatDomainError.

Examples:

BigDecimal.mode(BigDecimal::EXCEPTION_ALL, false)      # => 0
def flow_under
  x = BigDecimal('0.1')
  100.times { x *= x }
end
flow_under                                             # => 100
BigDecimal.mode(BigDecimal::EXCEPTION_UNDERFLOW, true) # => 4
flow_under # Raises FloatDomainError

Overflow

Mode BigDecimal::EXCEPTION_OVERFLOW controls behavior when a BigDecimal overflow occurs. Settings:

  • false (default): Returns BigDecimal('Infinity') or BigDecimal('-Infinity').

  • true: Raises FloatDomainError.

Examples:

BigDecimal.mode(BigDecimal::EXCEPTION_ALL, false)     # => 0
def flow_over
  x = BigDecimal('10')
  100.times { x *= x }
end
flow_over                                             # => 100
BigDecimal.mode(BigDecimal::EXCEPTION_OVERFLOW, true) # => 1
flow_over # Raises FloatDomainError

Zero Division

Mode BigDecimal::EXCEPTION_ZERODIVIDE controls behavior when a zero-division occurs. Settings:

  • false (default): Returns BigDecimal('Infinity') or BigDecimal('-Infinity').

  • true: Raises FloatDomainError.

Examples:

BigDecimal.mode(BigDecimal::EXCEPTION_ALL, false)       # => 0
one = BigDecimal('1')
zero = BigDecimal('0')
one / zero                                              # => Infinity
BigDecimal.mode(BigDecimal::EXCEPTION_ZERODIVIDE, true) # => 16
one / zero # Raises FloatDomainError

All Exceptions

Mode BigDecimal::EXCEPTION_ALL controls all of the above:

BigDecimal.mode(BigDecimal::EXCEPTION_ALL, false) # => 0
BigDecimal.mode(BigDecimal::EXCEPTION_ALL, true)  # => 23

Rounding

Mode BigDecimal::ROUND_MODE controls the way rounding is to be performed; its setting values are:

  • ROUND_UP: Round away from zero. Aliased as :up.

  • ROUND_DOWN: Round toward zero. Aliased as :down and :truncate.

  • ROUND_HALF_UP: Round toward the nearest neighbor; if the neighbors are equidistant, round away from zero. Aliased as :half_up and :default.

  • ROUND_HALF_DOWN: Round toward the nearest neighbor; if the neighbors are equidistant, round toward zero. Aliased as :half_down.

  • ROUND_HALF_EVEN (Banker’s rounding): Round toward the nearest neighbor; if the neighbors are equidistant, round toward the even neighbor. Aliased as :half_even and :banker.

  • ROUND_CEILING: Round toward positive infinity. Aliased as :ceiling and :ceil.

  • ROUND_FLOOR: Round toward negative infinity. Aliased as :floor:.

BigDecimal.save_exception_mode { ... }
::

Execute the provided block, but preserve the exception mode

BigDecimal.save_exception_mode do
  BigDecimal.mode(BigDecimal::EXCEPTION_OVERFLOW, false)
  BigDecimal.mode(BigDecimal::EXCEPTION_NaN, false)

  BigDecimal(BigDecimal('Infinity'))
  BigDecimal(BigDecimal('-Infinity'))
  BigDecimal(BigDecimal('NaN'))
end

For use with the BigDecimal::EXCEPTION_*

See BigDecimal.mode

BigDecimal.save_limit { ... }
::

Execute the provided block, but preserve the precision limit

BigDecimal.limit(100)
puts BigDecimal.limit
BigDecimal.save_limit do
    BigDecimal.limit(200)
    puts BigDecimal.limit
end
puts BigDecimal.limit

BigDecimal.save_rounding_mode { ... }
::

Execute the provided block, but preserve the rounding mode

BigDecimal.save_rounding_mode do
  BigDecimal.mode(BigDecimal::ROUND_MODE, :up)
  puts BigDecimal.mode(BigDecimal::ROUND_MODE)
end

For use with the BigDecimal::ROUND_*

See BigDecimal.mode

Instance Methods

a % b
#

Returns the modulus from dividing by b.

See BigDecimal#divmod.

*(p1)
#
No documentation available

self ** other → bigdecimal
#

Returns the BigDecimal value of self raised to power other:

b = BigDecimal('3.14')
b ** 2              # => 0.98596e1
b ** 2.0            # => 0.98596e1
b ** Rational(2, 1) # => 0.98596e1

Related: BigDecimal#power.

self + value → bigdecimal
#

Returns the BigDecimal sum of self and value:

b = BigDecimal('111111.111') # => 0.111111111e6
b + 2                        # => 0.111113111e6
b + 2.0                      # => 0.111113111e6
b + Rational(2, 1)           # => 0.111113111e6
b + Complex(2, 0)            # => (0.111113111e6+0i)

See the Note About Precision.

+big_decimal → self
#

Returns self:

+BigDecimal(5)  # => 0.5e1
+BigDecimal(-5) # => -0.5e1

self - value → bigdecimal
#

Returns the BigDecimal difference of self and value:

b = BigDecimal('333333.333') # => 0.333333333e6
b - 2                        # => 0.333331333e6
b - 2.0                      # => 0.333331333e6
b - Rational(2, 1)           # => 0.333331333e6
b - Complex(2, 0)            # => (0.333331333e6+0i)

See the Note About Precision.

-self → bigdecimal
#

Returns the BigDecimal negation of self:

b0 = BigDecimal('1.5')
b1 = -b0 # => -0.15e1
b2 = -b1 # => 0.15e1

a / b → bigdecimal
#

Divide by the specified value.

The result precision will be the precision of the larger operand, but its minimum is 2*Float::DIG.

See BigDecimal#div. See BigDecimal#quo.

self < other → true or false
#

Returns true if self is less than other, false otherwise:

b = BigDecimal('1.5') # => 0.15e1
b < 2                 # => true
b < 2.0               # => true
b < Rational(2, 1)    # => true
b < 1.5               # => false

Raises an exception if the comparison cannot be made.

self <= other → true or false
#

Returns true if self is less or equal to than other, false otherwise:

b = BigDecimal('1.5') # => 0.15e1
b <= 2                # => true
b <= 2.0              # => true
b <= Rational(2, 1)   # => true
b <= 1.5              # => true
b < 1                 # => false

Raises an exception if the comparison cannot be made.

<=>(p1)
#

The comparison operator. a <=> b is 0 if a == b, 1 if a > b, -1 if a < b.

==(p1)
#

Tests for value equality; returns true if the values are equal.

The == and === operators and the eql? method have the same implementation for BigDecimal.

Values may be coerced to perform the comparison:

BigDecimal('1.0') == 1.0  #=> true

===(p1)
#
An alias for ==

self > other → true or false
#

Returns true if self is greater than other, false otherwise:

b = BigDecimal('1.5')
b > 1              # => true
b > 1.0            # => true
b > Rational(1, 1) # => true
b > 2              # => false

Raises an exception if the comparison cannot be made.

self >= other → true or false
#

Returns true if self is greater than or equal to other, false otherwise:

b = BigDecimal('1.5')
b >= 1              # => true
b >= 1.0            # => true
b >= Rational(1, 1) # => true
b >= 1.5            # => true
b > 2               # => false

Raises an exception if the comparison cannot be made.

_dump → string
#

Returns a string representing the marshalling of self. See module Marshal.

inf = BigDecimal('Infinity') # => Infinity
dumped = inf._dump           # => "9:Infinity"
BigDecimal._load(dumped)     # => Infinity

abs → bigdecimal
#

Returns the BigDecimal absolute value of self:

BigDecimal('5').abs  # => 0.5e1
BigDecimal('-3').abs # => 0.3e1

add(value, ndigits) → new_bigdecimal
#

Returns the BigDecimal sum of self and value with a precision of ndigits decimal digits.

When ndigits is less than the number of significant digits in the sum, the sum is rounded to that number of digits, according to the current rounding mode; see BigDecimal.mode.

Examples:

# Set the rounding mode.
BigDecimal.mode(BigDecimal::ROUND_MODE, :half_up)
b = BigDecimal('111111.111')
b.add(1, 0)               # => 0.111112111e6
b.add(1, 3)               # => 0.111e6
b.add(1, 6)               # => 0.111112e6
b.add(1, 15)              # => 0.111112111e6
b.add(1.0, 15)            # => 0.111112111e6
b.add(Rational(1, 1), 15) # => 0.111112111e6

as_json(*)
#

Marshal the object to JSON.

method used for JSON marshalling support.

ceil(n)
#

Return the smallest integer greater than or equal to the value, as a BigDecimal.

BigDecimal('3.14159').ceil #=> 4
BigDecimal('-9.1').ceil #=> -9

If n is specified and positive, the fractional part of the result has no more than that many digits.

If n is specified and negative, at least that many digits to the left of the decimal point will be 0 in the result.

BigDecimal('3.14159').ceil(3) #=> 3.142
BigDecimal('13345.234').ceil(-2) #=> 13400.0

clone
#
No documentation available

coerce(p1)
#

The coerce method provides support for Ruby type coercion. It is not enabled by default.

This means that binary operations like + * / or - can often be performed on a BigDecimal and an object of another type, if the other object can be coerced into a BigDecimal value.

e.g.

a = BigDecimal("1.0")
b = a / 2.0 #=> 0.5

Note that coercing a String to a BigDecimal is not supported by default; it requires a special compile-time option when building Ruby.

div(value) → integer

div(value, digits) → bigdecimal or integer
#

Divide by the specified value.

digits

If specified and less than the number of significant digits of the result, the result is rounded to that number of digits, according to BigDecimal.mode.

If digits is 0, the result is the same as for the / operator or quo.

If digits is not specified, the result is an integer, by analogy with Float#div; see also BigDecimal#divmod.

See BigDecimal#/. See BigDecimal#quo.

Examples:

a = BigDecimal("4")
b = BigDecimal("3")

a.div(b, 3)  # => 0.133e1

a.div(b, 0)  # => 0.1333333333333333333e1
a / b        # => 0.1333333333333333333e1
a.quo(b)     # => 0.1333333333333333333e1

a.div(b)     # => 1

divmod(value)
#

Divides by the specified value, and returns the quotient and modulus as BigDecimal numbers. The quotient is rounded towards negative infinity.

For example:

require 'bigdecimal'

a = BigDecimal("42")
b = BigDecimal("9")

q, m = a.divmod(b)

c = q * b + m

a == c  #=> true

The quotient q is (a/b).floor, and the modulus is the amount that must be added to q * b to get a.

dup
#
An alias for clone

eql?(p1)
#
An alias for ==

exponent
#

Returns the exponent of the BigDecimal number, as an Integer.

If the number can be represented as 0.xxxxxx*10**n where xxxxxx is a string of digits with no leading zeros, then n is the exponent.

finite?
#

Returns True if the value is finite (not NaN or infinite).

fix
#

Return the integer part of the number, as a BigDecimal.

floor(n)
#

Return the largest integer less than or equal to the value, as a BigDecimal.

BigDecimal('3.14159').floor #=> 3
BigDecimal('-9.1').floor #=> -10

If n is specified and positive, the fractional part of the result has no more than that many digits.

If n is specified and negative, at least that many digits to the left of the decimal point will be 0 in the result.

BigDecimal('3.14159').floor(3) #=> 3.141
BigDecimal('13345.234').floor(-2) #=> 13300.0

frac
#

Return the fractional part of the number, as a BigDecimal.

hash → integer
#

Returns the integer hash value for self.

Two instances of BigDecimal have the same hash value if and only if they have equal:

  • Sign.

  • Fractional part.

  • Exponent.

infinite?
#

Returns nil, -1, or +1 depending on whether the value is finite, -Infinity, or +Infinity.

inspect
#

Returns a string representation of self.

BigDecimal("1234.5678").inspect
  #=> "0.12345678e4"

a.modulo(b)
#
An alias for %

mult(other, ndigits) → bigdecimal
#

Returns the BigDecimal product of self and value with a precision of ndigits decimal digits.

When ndigits is less than the number of significant digits in the sum, the sum is rounded to that number of digits, according to the current rounding mode; see BigDecimal.mode.

Examples:

# Set the rounding mode.
BigDecimal.mode(BigDecimal::ROUND_MODE, :half_up)
b = BigDecimal('555555.555')
b.mult(3, 0)              # => 0.1666666665e7
b.mult(3, 3)              # => 0.167e7
b.mult(3, 6)              # => 0.166667e7
b.mult(3, 15)             # => 0.1666666665e7
b.mult(3.0, 0)            # => 0.1666666665e7
b.mult(Rational(3, 1), 0) # => 0.1666666665e7
b.mult(Complex(3, 0), 0)  # => (0.1666666665e7+0.0i)

n_significant_digits → integer
#

Returns the number of decimal significant digits in self.

BigDecimal("0").n_significant_digits         # => 0
BigDecimal("1").n_significant_digits         # => 1
BigDecimal("1.1").n_significant_digits       # => 2
BigDecimal("3.1415").n_significant_digits    # => 5
BigDecimal("-1e20").n_significant_digits     # => 1
BigDecimal("1e-20").n_significant_digits     # => 1
BigDecimal("Infinity").n_significant_digits  # => 0
BigDecimal("-Infinity").n_significant_digits # => 0
BigDecimal("NaN").n_significant_digits       # => 0

nan?
#

Returns True if the value is Not a Number.

nonzero?
#

Returns self if the value is non-zero, nil otherwise.

power(n)

power(n, prec)
#

Returns the value raised to the power of n.

Note that n must be an Integer.

Also available as the operator **.

precision → integer
#

Returns the number of decimal digits in self:

BigDecimal("0").precision         # => 0
BigDecimal("1").precision         # => 1
BigDecimal("1.1").precision       # => 2
BigDecimal("3.1415").precision    # => 5
BigDecimal("-1e20").precision     # => 21
BigDecimal("1e-20").precision     # => 20
BigDecimal("Infinity").precision  # => 0
BigDecimal("-Infinity").precision # => 0
BigDecimal("NaN").precision       # => 0

precision_scale → [integer, integer]
#

Returns a 2-length array; the first item is the result of BigDecimal#precision and the second one is of BigDecimal#scale.

See BigDecimal#precision. See BigDecimal#scale.

precs → array
#

Returns an Array of two Integer values that represent platform-dependent internal storage properties.

This method is deprecated and will be removed in the future. Instead, use BigDecimal#n_significant_digits for obtaining the number of significant digits in scientific notation, and BigDecimal#precision for obtaining the number of digits in decimal notation.

quo(value) → bigdecimal

quo(value, digits) → bigdecimal
#

Divide by the specified value.

digits

If specified and less than the number of significant digits of the result, the result is rounded to the given number of digits, according to the rounding mode indicated by BigDecimal.mode.

If digits is 0 or omitted, the result is the same as for the / operator.

See BigDecimal#/. See BigDecimal#div.

remainder(value)
#

Returns the remainder from dividing by the value.

x.remainder(y) means x-y*(x/y).truncate

round(n, mode)
#

Round to the nearest integer (by default), returning the result as a BigDecimal if n is specified, or as an Integer if it isn’t.

BigDecimal('3.14159').round #=> 3
BigDecimal('8.7').round #=> 9
BigDecimal('-9.9').round #=> -10

BigDecimal('3.14159').round(2).class.name #=> "BigDecimal"
BigDecimal('3.14159').round.class.name #=> "Integer"

If n is specified and positive, the fractional part of the result has no more than that many digits.

If n is specified and negative, at least that many digits to the left of the decimal point will be 0 in the result, and return value will be an Integer.

BigDecimal('3.14159').round(3) #=> 3.142
BigDecimal('13345.234').round(-2) #=> 13300

The value of the optional mode argument can be used to determine how rounding is performed; see BigDecimal.mode.

scale → integer
#

Returns the number of decimal digits following the decimal digits in self.

BigDecimal("0").scale         # => 0
BigDecimal("1").scale         # => 1
BigDecimal("1.1").scale       # => 1
BigDecimal("3.1415").scale    # => 4
BigDecimal("-1e20").precision # => 0
BigDecimal("1e-20").precision # => 20
BigDecimal("Infinity").scale  # => 0
BigDecimal("-Infinity").scale # => 0
BigDecimal("NaN").scale       # => 0

sign
#

Returns the sign of the value.

Returns a positive value if > 0, a negative value if < 0. It behaves the same with zeros - it returns a positive value for a positive zero (BigDecimal(‘0’)) and a negative value for a negative zero (BigDecimal(‘-0’)).

The specific value returned indicates the type and sign of the BigDecimal, as follows:

BigDecimal::SIGN_NaN

value is Not a Number

BigDecimal::SIGN_POSITIVE_ZERO

value is +0

BigDecimal::SIGN_NEGATIVE_ZERO

value is -0

BigDecimal::SIGN_POSITIVE_INFINITE

value is +Infinity

BigDecimal::SIGN_NEGATIVE_INFINITE

value is -Infinity

BigDecimal::SIGN_POSITIVE_FINITE

value is positive

BigDecimal::SIGN_NEGATIVE_FINITE

value is negative

split
#

Splits a BigDecimal number into four parts, returned as an array of values.

The first value represents the sign of the BigDecimal, and is -1 or 1, or 0 if the BigDecimal is Not a Number.

The second value is a string representing the significant digits of the BigDecimal, with no leading zeros.

The third value is the base used for arithmetic (currently always 10) as an Integer.

The fourth value is an Integer exponent.

If the BigDecimal can be represented as 0.xxxxxx*10**n, then xxxxxx is the string of significant digits with no leading zeros, and n is the exponent.

From these values, you can translate a BigDecimal to a float as follows:

sign, significant_digits, base, exponent = a.split
f = sign * "0.#{significant_digits}".to_f * (base ** exponent)

(Note that the to_f method is provided as a more convenient way to translate a BigDecimal to a Float.)

sqrt(n)
#

Returns the square root of the value.

Result has at least n significant digits.

sub(value, digits) → bigdecimal
#

Subtract the specified value.

e.g.

c = a.sub(b,n)
digits

If specified and less than the number of significant digits of the result, the result is rounded to that number of digits, according to BigDecimal.mode.

a.to_d → bigdecimal
#

Returns self.

require 'bigdecimal/util'

d = BigDecimal("3.14")
d.to_d                       # => 0.314e1

a.to_digits → string
#

Converts a BigDecimal to a String of the form “nnnnnn.mmm”. This method is deprecated; use BigDecimal#to_s(“F”) instead.

require 'bigdecimal/util'

d = BigDecimal("3.14")
d.to_digits                  # => "3.14"

to_f
#

Returns a new Float object having approximately the same value as the BigDecimal number. Normal accuracy limits and built-in errors of binary Float arithmetic apply.

to_i
#

Returns the value as an Integer.

If the BigDecimal is infinity or NaN, raises FloatDomainError.

to_int
#
An alias for to_i

to_json(*args)
#

return the JSON value

to_r
#

Converts a BigDecimal to a Rational.

to_s(s)
#

Converts the value to a string.

The default format looks like 0.xxxxEnn.

The optional parameter s consists of either an integer; or an optional ‘+’ or ‘ ’, followed by an optional number, followed by an optional ‘E’ or ‘F’.

If there is a ‘+’ at the start of s, positive values are returned with a leading ‘+’.

A space at the start of s returns positive values with a leading space.

If s contains a number, a space is inserted after each group of that many fractional digits.

If s ends with an ‘E’, engineering notation (0.xxxxEnn) is used.

If s ends with an ‘F’, conventional floating point notation is used.

Examples:

BigDecimal('-123.45678901234567890').to_s('5F')
  #=> '-123.45678 90123 45678 9'

BigDecimal('123.45678901234567890').to_s('+8F')
  #=> '+123.45678901 23456789'

BigDecimal('123.45678901234567890').to_s(' F')
  #=> ' 123.4567890123456789'

truncate(n)
#

Truncate to the nearest integer (by default), returning the result as a BigDecimal.

BigDecimal('3.14159').truncate #=> 3
BigDecimal('8.7').truncate #=> 8
BigDecimal('-9.9').truncate #=> -9

If n is specified and positive, the fractional part of the result has no more than that many digits.

If n is specified and negative, at least that many digits to the left of the decimal point will be 0 in the result.

BigDecimal('3.14159').truncate(3) #=> 3.141
BigDecimal('13345.234').truncate(-2) #=> 13300.0

zero?
#

Returns True if the value is zero.