# Numbers

## 标准数值类型

### 抽象数值类型

Base.AbstractIrrationalType
AbstractIrrational <: Real

Number type representing an exact irrational value, which is automatically rounded to the correct precision in arithmetic operations with other numeric quantities.

Subtypes MyIrrational <: AbstractIrrational should implement at least ==(::MyIrrational, ::MyIrrational), hash(x::MyIrrational, h::UInt), and convert(::Type{F}, x::MyIrrational) where {F <: Union{BigFloat,Float32,Float64}}.

If a subtype is used to represent values that may occasionally be rational (e.g. a square-root type that represents √n for integers n will give a rational result when n is a perfect square), then it should also implement isinteger, iszero, isone, and == with Real values (since all of these default to false for AbstractIrrational types), as well as defining hash to equal that of the corresponding Rational.

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### 具象数值类型

Core.Float16Type
Float16 <: AbstractFloat

16-bit floating point number type (IEEE 754 standard).

Binary format: 1 sign, 5 exponent, 10 fraction bits.

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Core.Float32Type
Float32 <: AbstractFloat

32-bit floating point number type (IEEE 754 standard).

Binary format: 1 sign, 8 exponent, 23 fraction bits.

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Core.Float64Type
Float64 <: AbstractFloat

64-bit floating point number type (IEEE 754 standard).

Binary format: 1 sign, 11 exponent, 52 fraction bits.

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Core.BoolType
Bool <: Integer

Boolean type, containing the values true and false.

Bool is a kind of number: false is numerically equal to 0 and true is numerically equal to 1. Moreover, false acts as a multiplicative "strong zero":

julia> false == 0
true

julia> true == 1
true

julia> 0 * NaN
NaN

julia> false * NaN
0.0

See also: digits, iszero, NaN.

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Base.ComplexType
Complex{T<:Real} <: Number

Complex number type with real and imaginary part of type T.

ComplexF16, ComplexF32 and ComplexF64 are aliases for Complex{Float16}, Complex{Float32} and Complex{Float64} respectively.

See also: Real, complex, real.

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Base.RationalType
Rational{T<:Integer} <: Real

Rational number type, with numerator and denominator of type T. Rationals are checked for overflow.

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## 数据格式

Base.digitsFunction
digits([T<:Integer], n::Integer; base::T = 10, pad::Integer = 1)

Return an array with element type T (default Int) of the digits of n in the given base, optionally padded with zeros to a specified size. More significant digits are at higher indices, such that n == sum(digits[k]*base^(k-1) for k=1:length(digits)).

See also ndigits, digits!, and for base 2 also bitstring, count_ones.

Examples

julia> digits(10)
2-element Vector{Int64}:
0
1

julia> digits(10, base = 2)
4-element Vector{Int64}:
0
1
0
1

julia> digits(-256, base = 10, pad = 5)
5-element Vector{Int64}:
-6
-5
-2
0
0

julia> n = rand(-999:999);

julia> n == evalpoly(13, digits(n, base = 13))
true
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Base.digits!Function
digits!(array, n::Integer; base::Integer = 10)

Fills an array of the digits of n in the given base. More significant digits are at higher indices. If the array length is insufficient, the least significant digits are filled up to the array length. If the array length is excessive, the excess portion is filled with zeros.

Examples

julia> digits!([2, 2, 2, 2], 10, base = 2)
4-element Vector{Int64}:
0
1
0
1

julia> digits!([2, 2, 2, 2, 2, 2], 10, base = 2)
6-element Vector{Int64}:
0
1
0
1
0
0
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Base.bitstringFunction
bitstring(n)

A string giving the literal bit representation of a primitive type.

Examples

julia> bitstring(Int32(4))
"00000000000000000000000000000100"

julia> bitstring(2.2)
"0100000000000001100110011001100110011001100110011001100110011010"
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Base.parseFunction
parse(type, str; base)

Parse a string as a number. For Integer types, a base can be specified (the default is 10). For floating-point types, the string is parsed as a decimal floating-point number. Complex types are parsed from decimal strings of the form "R±Iim" as a Complex(R,I) of the requested type; "i" or "j" can also be used instead of "im", and "R" or "Iim" are also permitted. If the string does not contain a valid number, an error is raised.

Julia 1.1

parse(Bool, str) requires at least Julia 1.1.

Examples

julia> parse(Int, "1234")
1234

julia> parse(Int, "1234", base = 5)
194

julia> parse(Int, "afc", base = 16)
2812

julia> parse(Float64, "1.2e-3")
0.0012

julia> parse(Complex{Float64}, "3.2e-1 + 4.5im")
0.32 + 4.5im
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parse(::Type{Platform}, triplet::AbstractString)

Parses a string platform triplet back into a Platform object.

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Base.signedFunction
signed(T::Integer)

Convert an integer bitstype to the signed type of the same size.

Examples

julia> signed(UInt16)
Int16
julia> signed(UInt64)
Int64
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signed(x)

Convert a number to a signed integer. If the argument is unsigned, it is reinterpreted as signed without checking for overflow.

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Base.unsignedFunction
unsigned(T::Integer)

Convert an integer bitstype to the unsigned type of the same size.

Examples

julia> unsigned(Int16)
UInt16
julia> unsigned(UInt64)
UInt64
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Base.floatMethod
float(x)

Convert a number or array to a floating point data type.

Examples

julia> float(1:1000)
1.0:1.0:1000.0

julia> float(typemax(Int32))
2.147483647e9
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Base.Math.significandFunction
significand(x)

Extract the significand (a.k.a. mantissa) of a floating-point number. If x is a non-zero finite number, then the result will be a number of the same type and sign as x, and whose absolute value is on the interval $[1,2)$. Otherwise x is returned.

Examples

julia> significand(15.2)
1.9

julia> significand(-15.2)
-1.9

julia> significand(-15.2) * 2^3
-15.2

julia> significand(-Inf), significand(Inf), significand(NaN)
(-Inf, Inf, NaN)
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Base.Math.exponentFunction
exponent(x::AbstractFloat) -> Int

Get the exponent of a normalized floating-point number. Returns the largest integer y such that 2^y ≤ abs(x).

Examples

julia> exponent(6.5)
2

julia> exponent(16.0)
4
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Base.complexMethod
complex(r, [i])

Convert real numbers or arrays to complex. i defaults to zero.

Examples

julia> complex(7)
7 + 0im

julia> complex([1, 2, 3])
3-element Vector{Complex{Int64}}:
1 + 0im
2 + 0im
3 + 0im
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Base.bswapFunction
bswap(n)

Reverse the byte order of n.

(See also ntoh and hton to convert between the current native byte order and big-endian order.)

Examples

julia> a = bswap(0x10203040)
0x40302010

julia> bswap(a)
0x10203040

julia> string(1, base = 2)
"1"

julia> string(bswap(1), base = 2)
"100000000000000000000000000000000000000000000000000000000"
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Base.hex2bytesFunction
hex2bytes(itr)

Given an iterable itr of ASCII codes for a sequence of hexadecimal digits, returns a Vector{UInt8} of bytes corresponding to the binary representation: each successive pair of hexadecimal digits in itr gives the value of one byte in the return vector.

The length of itr must be even, and the returned array has half of the length of itr. See also hex2bytes! for an in-place version, and bytes2hex for the inverse.

Julia 1.7

Calling hex2bytes with iterators producing UInt8 values requires Julia 1.7 or later. In earlier versions, you can collect the iterator before calling hex2bytes.

Examples

julia> s = string(12345, base = 16)
"3039"

julia> hex2bytes(s)
2-element Vector{UInt8}:
0x30
0x39

julia> a = b"01abEF"
6-element Base.CodeUnits{UInt8, String}:
0x30
0x31
0x61
0x62
0x45
0x46

julia> hex2bytes(a)
3-element Vector{UInt8}:
0x01
0xab
0xef
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Base.hex2bytes!Function
hex2bytes!(dest::AbstractVector{UInt8}, itr)

Convert an iterable itr of bytes representing a hexadecimal string to its binary representation, similar to hex2bytes except that the output is written in-place to dest. The length of dest must be half the length of itr.

Julia 1.7

Calling hex2bytes! with iterators producing UInt8 requires version 1.7. In earlier versions, you can collect the iterable before calling instead.

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Base.bytes2hexFunction
bytes2hex(itr) -> String
bytes2hex(io::IO, itr)

Convert an iterator itr of bytes to its hexadecimal string representation, either returning a String via bytes2hex(itr) or writing the string to an io stream via bytes2hex(io, itr). The hexadecimal characters are all lowercase.

Julia 1.7

Calling bytes2hex with arbitrary iterators producing UInt8 values requires Julia 1.7 or later. In earlier versions, you can collect the iterator before calling bytes2hex.

Examples

julia> a = string(12345, base = 16)
"3039"

julia> b = hex2bytes(a)
2-element Vector{UInt8}:
0x30
0x39

julia> bytes2hex(b)
"3039"
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## 常用数值函数和常量

Base.oneFunction
one(x)
one(T::type)

Return a multiplicative identity for x: a value such that one(x)*x == x*one(x) == x. Alternatively one(T) can take a type T, in which case one returns a multiplicative identity for any x of type T.

If possible, one(x) returns a value of the same type as x, and one(T) returns a value of type T. However, this may not be the case for types representing dimensionful quantities (e.g. time in days), since the multiplicative identity must be dimensionless. In that case, one(x) should return an identity value of the same precision (and shape, for matrices) as x.

If you want a quantity that is of the same type as x, or of type T, even if x is dimensionful, use oneunit instead.

See also the identity function, and I in LinearAlgebra for the identity matrix.

Examples

julia> one(3.7)
1.0

julia> one(Int)
1

julia> import Dates; one(Dates.Day(1))
1
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Base.oneunitFunction
oneunit(x::T)
oneunit(T::Type)

Returns T(one(x)), where T is either the type of the argument or (if a type is passed) the argument. This differs from one for dimensionful quantities: one is dimensionless (a multiplicative identity) while oneunit is dimensionful (of the same type as x, or of type T).

Examples

julia> oneunit(3.7)
1.0

julia> import Dates; oneunit(Dates.Day)
1 day
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Base.zeroFunction
zero(x)
zero(::Type)

Get the additive identity element for the type of x (x can also specify the type itself).

Examples

julia> zero(1)
0

julia> zero(big"2.0")
0.0

julia> zero(rand(2,2))
2×2 Matrix{Float64}:
0.0  0.0
0.0  0.0
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Base.MathConstants.piConstant
π
pi

The constant pi.

Unicode π can be typed by writing \pi then pressing tab in the Julia REPL, and in many editors.

Examples

julia> pi
π = 3.1415926535897...

julia> 1/2pi
0.15915494309189535
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Base.MathConstants.catalanConstant
catalan

Catalan's constant.

Examples

julia> Base.MathConstants.catalan
catalan = 0.9159655941772...

julia> sum(log(x)/(1+x^2) for x in 1:0.01:10^6) * 0.01
0.9159466120554123
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Base.MathConstants.eulergammaConstant
γ
eulergamma

Euler's constant.

Examples

julia> Base.MathConstants.eulergamma
γ = 0.5772156649015...

julia> dx = 10^-6;

julia> sum(-exp(-x) * log(x) for x in dx:dx:100) * dx
0.5772078382499133
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Base.MathConstants.goldenConstant
φ
golden

The golden ratio.

Examples

julia> Base.MathConstants.golden
φ = 1.6180339887498...

julia> (2ans - 1)^2 ≈ 5
true
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Base.NaNConstant
NaN, NaN64

A not-a-number value of type Float64.

Examples

julia> 0/0
NaN

julia> Inf - Inf
NaN

julia> NaN == NaN, isequal(NaN, NaN), NaN === NaN
(false, true, true)
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Base.isfiniteFunction
isfinite(f) -> Bool

Test whether a number is finite.

Examples

julia> isfinite(5)
true

julia> isfinite(NaN32)
false
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Base.isnanFunction
isnan(f) -> Bool

Test whether a number value is a NaN, an indeterminate value which is neither an infinity nor a finite number ("not a number").

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Base.iszeroFunction
iszero(x)

Return true if x == zero(x); if x is an array, this checks whether all of the elements of x are zero.

Examples

julia> iszero(0.0)
true

julia> iszero([1, 9, 0])
false

julia> iszero([false, 0, 0])
true
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Base.isoneFunction
isone(x)

Return true if x == one(x); if x is an array, this checks whether x is an identity matrix.

Examples

julia> isone(1.0)
true

julia> isone([1 0; 0 2])
false

julia> isone([1 0; 0 true])
true
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Base.nextfloatFunction
nextfloat(x::AbstractFloat, n::Integer)

The result of n iterative applications of nextfloat to x if n >= 0, or -n applications of prevfloat if n < 0.

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nextfloat(x::AbstractFloat)

Return the smallest floating point number y of the same type as x such x < y. If no such y exists (e.g. if x is Inf or NaN), then return x.

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Base.prevfloatFunction
prevfloat(x::AbstractFloat, n::Integer)

The result of n iterative applications of prevfloat to x if n >= 0, or -n applications of nextfloat if n < 0.

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prevfloat(x::AbstractFloat)

Return the largest floating point number y of the same type as x such y < x. If no such y exists (e.g. if x is -Inf or NaN), then return x.

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Base.isintegerFunction
isinteger(x) -> Bool

Test whether x is numerically equal to some integer.

Examples

julia> isinteger(4.0)
true
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Base.isrealFunction
isreal(x) -> Bool

Test whether x or all its elements are numerically equal to some real number including infinities and NaNs. isreal(x) is true if isequal(x, real(x)) is true.

Examples

julia> isreal(5.)
true

julia> isreal(Inf + 0im)
true

julia> isreal([4.; complex(0,1)])
false
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Core.Float32Method
Float32(x [, mode::RoundingMode])

Create a Float32 from x. If x is not exactly representable then mode determines how x is rounded.

Examples

julia> Float32(1/3, RoundDown)
0.3333333f0

julia> Float32(1/3, RoundUp)
0.33333334f0

See RoundingMode for available rounding modes.

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Core.Float64Method
Float64(x [, mode::RoundingMode])

Create a Float64 from x. If x is not exactly representable then mode determines how x is rounded.

Examples

julia> Float64(pi, RoundDown)
3.141592653589793

julia> Float64(pi, RoundUp)
3.1415926535897936

See RoundingMode for available rounding modes.

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Base.Rounding.setroundingMethod
setrounding(T, mode)

Set the rounding mode of floating point type T, controlling the rounding of basic arithmetic functions (+, -, *, / and sqrt) and type conversion. Other numerical functions may give incorrect or invalid values when using rounding modes other than the default RoundNearest.

Note that this is currently only supported for T == BigFloat.

Warning

This function is not thread-safe. It will affect code running on all threads, but its behavior is undefined if called concurrently with computations that use the setting.

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Base.Rounding.setroundingMethod
setrounding(f::Function, T, mode)

Change the rounding mode of floating point type T for the duration of f. It is logically equivalent to:

old = rounding(T)
setrounding(T, mode)
f()
setrounding(T, old)

See RoundingMode for available rounding modes.

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Base.Rounding.get_zero_subnormalsFunction
get_zero_subnormals() -> Bool

Return false if operations on subnormal floating-point values ("denormals") obey rules for IEEE arithmetic, and true if they might be converted to zeros.

Warning

This function only affects the current thread.

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Base.Rounding.set_zero_subnormalsFunction
set_zero_subnormals(yes::Bool) -> Bool

If yes is false, subsequent floating-point operations follow rules for IEEE arithmetic on subnormal values ("denormals"). Otherwise, floating-point operations are permitted (but not required) to convert subnormal inputs or outputs to zero. Returns true unless yes==true but the hardware does not support zeroing of subnormal numbers.

set_zero_subnormals(true) can speed up some computations on some hardware. However, it can break identities such as (x-y==0) == (x==y).

Warning

This function only affects the current thread.

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### 整型

Base.count_onesFunction
count_ones(x::Integer) -> Integer

Number of ones in the binary representation of x.

Examples

julia> count_ones(7)
3

julia> count_ones(Int32(-1))
32
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Base.count_zerosFunction
count_zeros(x::Integer) -> Integer

Number of zeros in the binary representation of x.

Examples

julia> count_zeros(Int32(2 ^ 16 - 1))
16

julia> count_zeros(-1)
0
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Base.leading_zerosFunction
leading_zeros(x::Integer) -> Integer

Number of zeros leading the binary representation of x.

Examples

julia> leading_zeros(Int32(1))
31
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Base.leading_onesFunction
leading_ones(x::Integer) -> Integer

Number of ones leading the binary representation of x.

Examples

julia> leading_ones(UInt32(2 ^ 32 - 2))
31
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Base.trailing_zerosFunction
trailing_zeros(x::Integer) -> Integer

Number of zeros trailing the binary representation of x.

Examples

julia> trailing_zeros(2)
1
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Base.trailing_onesFunction
trailing_ones(x::Integer) -> Integer

Number of ones trailing the binary representation of x.

Examples

julia> trailing_ones(3)
2
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Base.isoddFunction
isodd(x::Number) -> Bool

Return true if x is an odd integer (that is, an integer not divisible by 2), and false otherwise.

Julia 1.7

Non-Integer arguments require Julia 1.7 or later.

Examples

julia> isodd(9)
true

julia> isodd(10)
false
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Base.isevenFunction
iseven(x::Number) -> Bool

Return true if x is an even integer (that is, an integer divisible by 2), and false otherwise.

Julia 1.7

Non-Integer arguments require Julia 1.7 or later.

Examples

julia> iseven(9)
false

julia> iseven(10)
true
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Core.@int128_strMacro
@int128_str str
@int128_str(str)

@int128_str parses a string into a Int128. Throws an ArgumentError if the string is not a valid integer.

source
Core.@uint128_strMacro
@uint128_str str
@uint128_str(str)

@uint128_str parses a string into a UInt128. Throws an ArgumentError if the string is not a valid integer.

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## BigFloats and BigInts

The BigFloat and BigInt types implements arbitrary-precision floating point and integer arithmetic, respectively. For BigFloat the GNU MPFR library is used, and for BigInt the GNU Multiple Precision Arithmetic Library (GMP) is used.

Base.MPFR.BigFloatMethod
BigFloat(x::Union{Real, AbstractString} [, rounding::RoundingMode=rounding(BigFloat)]; [precision::Integer=precision(BigFloat)])

Create an arbitrary precision floating point number from x, with precision precision. The rounding argument specifies the direction in which the result should be rounded if the conversion cannot be done exactly. If not provided, these are set by the current global values.

BigFloat(x::Real) is the same as convert(BigFloat,x), except if x itself is already BigFloat, in which case it will return a value with the precision set to the current global precision; convert will always return x.

BigFloat(x::AbstractString) is identical to parse. This is provided for convenience since decimal literals are converted to Float64 when parsed, so BigFloat(2.1) may not yield what you expect.

Julia 1.1

precision as a keyword argument requires at least Julia 1.1. In Julia 1.0 precision is the second positional argument (BigFloat(x, precision)).

Examples

julia> BigFloat(2.1) # 2.1 here is a Float64
2.100000000000000088817841970012523233890533447265625

julia> BigFloat("2.1") # the closest BigFloat to 2.1
2.099999999999999999999999999999999999999999999999999999999999999999999999999986

julia> BigFloat("2.1", RoundUp)
2.100000000000000000000000000000000000000000000000000000000000000000000000000021

julia> BigFloat("2.1", RoundUp, precision=128)
2.100000000000000000000000000000000000007
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Base.precisionFunction
precision(num::AbstractFloat; base::Integer=2)
precision(T::Type; base::Integer=2)

Get the precision of a floating point number, as defined by the effective number of bits in the significand, or the precision of a floating-point type T (its current default, if T is a variable-precision type like BigFloat).

If base is specified, then it returns the maximum corresponding number of significand digits in that base.

Julia 1.8

The base keyword requires at least Julia 1.8.

source
Missing docstring.

Missing docstring for Base.MPFR.precision(::Type{BigFloat}). Check Documenter's build log for details.

Base.MPFR.setprecisionFunction
setprecision([T=BigFloat,] precision::Int; base=2)

Set the precision (in bits, by default) to be used for T arithmetic. If base is specified, then the precision is the minimum required to give at least precision digits in the given base.

Warning

This function is not thread-safe. It will affect code running on all threads, but its behavior is undefined if called concurrently with computations that use the setting.

Julia 1.8

The base keyword requires at least Julia 1.8.

source
setprecision(f::Function, [T=BigFloat,] precision::Integer; base=2)

Change the T arithmetic precision (in the given base) for the duration of f. It is logically equivalent to:

old = precision(BigFloat)
setprecision(BigFloat, precision)
f()
setprecision(BigFloat, old)

Often used as setprecision(T, precision) do ... end

Note: nextfloat(), prevfloat() do not use the precision mentioned by setprecision.

Julia 1.8

The base keyword requires at least Julia 1.8.

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Base.GMP.BigIntMethod
BigInt(x)

Create an arbitrary precision integer. x may be an Int (or anything that can be converted to an Int). The usual mathematical operators are defined for this type, and results are promoted to a BigInt.

Instances can be constructed from strings via parse, or using the big string literal.

Examples

julia> parse(BigInt, "42")
42

julia> big"313"
313

julia> BigInt(10)^19
10000000000000000000
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Core.@big_strMacro
@big_str str
@big_str(str)

Parse a string into a BigInt or BigFloat, and throw an ArgumentError if the string is not a valid number. For integers _ is allowed in the string as a separator.

Examples

julia> big"123_456"
123456

julia> big"7891.5"
7891.5
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