# This file is a part of Julia. License is MIT: https://julialang.org/license

module Math

export sin, cos, sincos, tan, sinh, cosh, tanh, asin, acos, atan,
       asinh, acosh, atanh, sec, csc, cot, asec, acsc, acot,
       sech, csch, coth, asech, acsch, acoth,
       sinpi, cospi, sincospi, tanpi, sinc, cosc,
       cosd, cotd, cscd, secd, sind, tand, sincosd,
       acosd, acotd, acscd, asecd, asind, atand,
       rad2deg, deg2rad,
       log, log2, log10, log1p, exponent, exp, exp2, exp10, expm1,
       cbrt, sqrt, fourthroot, significand,
       hypot, max, min, minmax, ldexp, frexp,
       clamp, clamp!, modf, ^, mod2pi, rem2pi,
       @evalpoly, evalpoly

import .Base: log, exp, sin, cos, tan, sinh, cosh, tanh, asin,
             acos, atan, asinh, acosh, atanh, sqrt, log2, log10,
             max, min, minmax, ^, exp2, muladd, rem,
             exp10, expm1, log1p, @constprop, @assume_effects

using .Base: sign_mask, exponent_mask, exponent_one,
            exponent_half, uinttype, significand_mask,
            significand_bits, exponent_bits, exponent_bias,
            exponent_raw_max, clamp, clamp!, two_mul

using Core.Intrinsics: sqrt_llvm, min_float, max_float

using .Base: IEEEFloat

@noinline function throw_complex_domainerror(f::Symbol, x)
    throw(DomainError(x,
        LazyString(f," was called with a negative real argument but will only return a complex result if called with a complex argument. Try ", f,"(Complex(x)).")))
end
@noinline function throw_complex_domainerror_neg1(f::Symbol, x)
    throw(DomainError(x,
        LazyString(f," was called with a real argument < -1 but will only return a complex result if called with a complex argument. Try ", f,"(Complex(x)).")))
end
@noinline function throw_exp_domainerror(x)
    throw(DomainError(x, LazyString(
        "Exponentiation yielding a complex result requires a ",
        "complex argument.\nReplace x^y with (x+0im)^y, ",
        "Complex(x)^y, or similar.")))
end

# non-type specific math functions

"""
    evalpoly(x, p)

Evaluate the polynomial ``\\sum_k x^{k-1} p[k]`` for the coefficients `p[1]`, `p[2]`, ...;
that is, the coefficients are given in ascending order by power of `x`.
Loops are unrolled at compile time if the number of coefficients is statically known, i.e.
when `p` is a `Tuple`.
This function generates efficient code using Horner's method if `x` is real, or using
a Goertzel-like [^DK62] algorithm if `x` is complex.

[^DK62]: Donald Knuth, Art of Computer Programming, Volume 2: Seminumerical Algorithms, Sec. 4.6.4.

!!! compat "Julia 1.4"
    This function requires Julia 1.4 or later.

See also [`@evalpoly`](@ref).

# Examples
```jldoctest
julia> evalpoly(2, (1, 2, 3))
17
```
"""
function evalpoly(x, p::Tuple)
    if @generated
        N = length(p.parameters::Core.SimpleVector)
        ex = :(p[end])
        for i in N-1:-1:1
            ex = :(muladd(x, $ex, p[$i]))
        end
        ex
    else
        _evalpoly(x, p)
    end
end

evalpoly(x, p::AbstractVector) = _evalpoly(x, p)

function _evalpoly(x, p)
    Base.require_one_based_indexing(p)
    N = length(p)
    ex = p[end]
    for i in N-1:-1:1
        ex = muladd(x, ex, p[i])
    end
    ex
end

function evalpoly(z::Complex, p::Tuple)
    if @generated
        N = length(p.parameters)
        a = :(p[end])
        b = :(p[end-1])
        as = []
        for i in N-2:-1:1
            ai = Symbol("a", i)
            push!(as, :($ai = $a))
            a = :(muladd(r, $ai, $b))
            b = :(muladd(-s, $ai, p[$i]))
        end
        ai = :a0
        push!(as, :($ai = $a))
        Expr(:block,
             :(x = real(z)),
             :(y = imag(z)),
             :(r = x + x),
             :(s = muladd(x, x, y*y)),
             as...,
             :(muladd($ai, z, $b)))
    else
        _evalpoly(z, p)
    end
end
evalpoly(z::Complex, p::Tuple{<:Any}) = p[1]


evalpoly(z::Complex, p::AbstractVector) = _evalpoly(z, p)

function _evalpoly(z::Complex, p)
    Base.require_one_based_indexing(p)
    length(p) == 1 && return p[1]
    N = length(p)
    a = p[end]
    b = p[end-1]

    x = real(z)
    y = imag(z)
    r = 2x
    s = muladd(x, x, y*y)
    for i in N-2:-1:1
        ai = a
        a = muladd(r, ai, b)
        b = muladd(-s, ai, p[i])
    end
    ai = a
    muladd(ai, z, b)
end

"""
    @horner(x, p...)

Evaluate `p[1] + x * (p[2] + x * (....))`, i.e. a polynomial via Horner's rule.

See also [`@evalpoly`](@ref), [`evalpoly`](@ref).
"""
macro horner(x, p...)
     xesc, pesc = esc(x), esc.(p)
    :(invoke(evalpoly, Tuple{Any, Tuple}, $xesc, ($(pesc...),)))
end

# Evaluate p[1] + z*p[2] + z^2*p[3] + ... + z^(n-1)*p[n].  This uses
# Horner's method if z is real, but for complex z it uses a more
# efficient algorithm described in Knuth, TAOCP vol. 2, section 4.6.4,
# equation (3).

"""
    @evalpoly(z, c...)

Evaluate the polynomial ``\\sum_k z^{k-1} c[k]`` for the coefficients `c[1]`, `c[2]`, ...;
that is, the coefficients are given in ascending order by power of `z`.  This macro expands
to efficient inline code that uses either Horner's method or, for complex `z`, a more
efficient Goertzel-like algorithm.

See also [`evalpoly`](@ref).

# Examples
```jldoctest
julia> @evalpoly(3, 1, 0, 1)
10

julia> @evalpoly(2, 1, 0, 1)
5

julia> @evalpoly(2, 1, 1, 1)
7
```
"""
macro evalpoly(z, p...)
    zesc, pesc = esc(z), esc.(p)
    :(evalpoly($zesc, ($(pesc...),)))
end

# polynomial evaluation using compensated summation.
# much more accurate, especially when lo can be combined with other rounding errors
@inline function exthorner(x::T, p::Tuple{T,T,T}) where T<:Union{Float32,Float64}
    hi, lo = p[lastindex(p)], zero(x)
    hi, lo = _exthorner(2, x, p, hi, lo)
    hi, lo = _exthorner(1, x, p, hi, lo)
    return hi, lo
end

@inline function _exthorner(i::Int, x::T, p::Tuple{T,T,T}, hi::T, lo::T) where T<:Union{Float32,Float64}
    i == 2 || i == 1 || error("unexpected index")
    pi = p[i]
    prod, err = two_mul(hi,x)
    hi = pi+prod
    lo = fma(lo, x, prod - (hi - pi) + err)
    return hi, lo
end

# generic, but involves double rounding
function _180_over_pi(z::AbstractFloat)
    180 / oftype(z, pi)
end
function _pi_over_180(z::AbstractFloat)
    oftype(z, pi) / 180
end

# rounded to closest representable number where necessary
_180_over_pi(::Float16) = Float16(57.28)
_180_over_pi(::Float32) = 57.29578f0
_pi_over_180(::Float16) = Float16(0.01746)

"""
    rad2deg(x)

Convert `x` from radians to degrees.

See also [`deg2rad`](@ref), [`pi`](@ref).

# Examples
```jldoctest
julia> rad2deg(pi)
180.0
```
"""
rad2deg(z::AbstractFloat) = z * _180_over_pi(z)

"""
    deg2rad(x)

Convert `x` from degrees to radians.

See also [`rad2deg`](@ref), [`pi`](@ref).

# Examples
```jldoctest
julia> deg2rad(90)
1.5707963267948966
```
"""
deg2rad(z::AbstractFloat) = z * _pi_over_180(z)
rad2deg(z::Real) = rad2deg(float(z))
deg2rad(z::Real) = deg2rad(float(z))
rad2deg(z::Number) = (z/pi)*180
deg2rad(z::Number) = (z*pi)/180

log(b::T, x::T) where {T<:Number} = log(x)/log(b)

"""
    log(b,x)

Compute the base `b` logarithm of `x`. Throw a [`DomainError`](@ref) for negative
[`Real`](@ref) arguments.

See also [`log2`](@ref), [`log10`](@ref).

# Examples
```jldoctest; filter = r"Stacktrace:(\\n \\[[0-9]+\\].*)*"
julia> log(4,8)
1.5

julia> log(4,2)
0.5

julia> log(-2, 3)
ERROR: DomainError with -2.0:
log was called with a negative real argument but will only return a complex result if called with a complex argument. Try log(Complex(x)).
Stacktrace:
 [1] throw_complex_domainerror(::Symbol, ::Float64) at ./math.jl:31
[...]

julia> log(2, -3)
ERROR: DomainError with -3.0:
log was called with a negative real argument but will only return a complex result if called with a complex argument. Try log(Complex(x)).
Stacktrace:
 [1] throw_complex_domainerror(::Symbol, ::Float64) at ./math.jl:31
[...]
```

!!! note
    If `b` is a power of 2 or 10, [`log2`](@ref) or [`log10`](@ref) should be used, as these will
    typically be faster and more accurate. For example,

    ```jldoctest
    julia> log(100,1000000)
    2.9999999999999996

    julia> log10(1000000)/2
    3.0
    ```
"""
log(b::Number, x::Number) = log(promote(b,x)...)

const libm = Base.libm_name
# functions with no domain error
"""
    sinh(x)

Compute hyperbolic sine of `x`.

See also [`sin`](@ref), [`asinh`](@ref).
"""
sinh(x::Number)

"""
    cosh(x)

Compute hyperbolic cosine of `x`.

See also [`cos`](@ref), [`acosh`](@ref).
"""
cosh(x::Number)

"""
    tanh(x)

Compute hyperbolic tangent of `x`.

See also [`tan`](@ref), [`atanh`](@ref).

# Examples

```jldoctest
julia> tanh.(-3:3f0)  # Here 3f0 isa Float32
7-element Vector{Float32}:
 -0.9950548
 -0.9640276
 -0.7615942
  0.0
  0.7615942
  0.9640276
  0.9950548

julia> tan.(im .* (1:3))
3-element Vector{ComplexF64}:
 0.0 + 0.7615941559557649im
 0.0 + 0.9640275800758169im
 0.0 + 0.9950547536867306im
```
"""
tanh(x::Number)

"""
    atan(y)
    atan(y, x)

Compute the inverse tangent of `y` or `y/x`, respectively.

For one real argument, this is the angle in radians between the positive *x*-axis and the point
(1, *y*), returning a value in the interval ``[-\\pi/2, \\pi/2]``.

For two arguments, this is the angle in radians between the positive *x*-axis and the
point (*x*, *y*), returning a value in the interval ``[-\\pi, \\pi]``. This corresponds to a
standard [`atan2`](https://en.wikipedia.org/wiki/Atan2) function. Note that by convention
`atan(0.0,x)` is defined as ``\\pi`` and `atan(-0.0,x)` is defined as ``-\\pi`` when `x < 0`.

See also [`atand`](@ref) for degrees.

# Examples

```jldoctest
julia> rad2deg(atan(-1/√3))
-30.000000000000004

julia> rad2deg(atan(-1, √3))
-30.000000000000004

julia> rad2deg(atan(1, -√3))
150.0
```
"""
atan(x::Number)

"""
    asinh(x)

Compute the inverse hyperbolic sine of `x`.

See also [`sinh`](@ref), [`asin`](@ref).
"""
asinh(x::Number)


# utility for converting NaN return to DomainError
# the branch in nan_dom_err prevents its callers from inlining, so be sure to force it
# until the heuristics can be improved
@inline nan_dom_err(out, x) = isnan(out) & !isnan(x) ? throw(DomainError(x, "NaN result for non-NaN input.")) : out

# functions that return NaN on non-NaN argument for domain error
"""
    sin(x::T) where {T <: Number} -> float(T)

Compute sine of `x`, where `x` is in radians.

Throw a [`DomainError`](@ref) if `isinf(x)`, return a `T(NaN)` if `isnan(x)`.

See also [`sind`](@ref), [`sinpi`](@ref), [`sincos`](@ref), [`cis`](@ref), [`asin`](@ref).

# Examples
```jldoctest
julia> round.(sin.(range(0, 2pi, length=9)'), digits=3)
1×9 Matrix{Float64}:
 0.0  0.707  1.0  0.707  0.0  -0.707  -1.0  -0.707  -0.0

julia> sind(45)
0.7071067811865476

julia> sinpi(1/4)
0.7071067811865476

julia> round.(sincos(pi/6), digits=3)
(0.5, 0.866)

julia> round(cis(pi/6), digits=3)
0.866 + 0.5im

julia> round(exp(im*pi/6), digits=3)
0.866 + 0.5im
```
"""
sin(x::Number)

"""
    cos(x::T) where {T <: Number} -> float(T)

Compute cosine of `x`, where `x` is in radians.

Throw a [`DomainError`](@ref) if `isinf(x)`, return a `T(NaN)` if `isnan(x)`.

See also [`cosd`](@ref), [`cospi`](@ref), [`sincos`](@ref), [`cis`](@ref), [`acos`](@ref).
"""
cos(x::Number)

"""
    tan(x::T) where {T <: Number} -> float(T)

Compute tangent of `x`, where `x` is in radians.

Throw a [`DomainError`](@ref) if `isinf(x)`, return a `T(NaN)` if `isnan(x)`.

See also [`tanh`](@ref).
"""
tan(x::Number)

"""
    asin(x::T) where {T <: Number} -> float(T)

Compute the inverse sine of `x`, where the output is in radians.

Return a `T(NaN)` if `isnan(x)`.

See also [`asind`](@ref) for output in degrees.

# Examples
```jldoctest
julia> asin.((0, 1/2, 1))
(0.0, 0.5235987755982989, 1.5707963267948966)

julia> asind.((0, 1/2, 1))
(0.0, 30.000000000000004, 90.0)
```
"""
asin(x::Number)

"""
    acos(x::T) where {T <: Number} -> float(T)

Compute the inverse cosine of `x`, where the output is in radians.

Return a `T(NaN)` if `isnan(x)`.

See also [`acosd`](@ref) for output in degrees.
"""
acos(x::Number)

"""
    acosh(x)

Compute the inverse hyperbolic cosine of `x`.

See also [`cosh`](@ref), [`acos`](@ref).
"""
acosh(x::Number)

"""
    atanh(x)

Compute the inverse hyperbolic tangent of `x`.

See also [`tanh`](@ref), [`atanh`](@ref).
"""
atanh(x::Number)

"""
    log(x)

Compute the natural logarithm of `x`.

Throw a [`DomainError`](@ref) for negative [`Real`](@ref) arguments.
Use [`Complex`](@ref) arguments to obtain [`Complex`](@ref) results.

!!! note "Branch cut"
    `log` has a branch cut along the negative real axis; `-0.0im` is taken
    to be below the axis.

See also [`ℯ`](@ref), [`exp`](@ref), [`log1p`](@ref), [`log2`](@ref), [`log10`](@ref).

# Examples
```jldoctest; filter = r"Stacktrace:(\\n \\[[0-9]+\\].*)*"
julia> log(2)
0.6931471805599453

julia> log(-3)
ERROR: DomainError with -3.0:
log was called with a negative real argument but will only return a complex result if called with a complex argument. Try log(Complex(x)).
Stacktrace:
 [1] throw_complex_domainerror(::Symbol, ::Float64) at ./math.jl:31
[...]

julia> log(-3 + 0im)
1.0986122886681098 + 3.141592653589793im

julia> log(-3 - 0.0im)
1.0986122886681098 - 3.141592653589793im

julia> log.(exp.(-1:1))
3-element Vector{Float64}:
 -1.0
  0.0
  1.0
```
"""
log(x::Number)

"""
    log2(x)

Compute the logarithm of `x` to base 2. Throw a [`DomainError`](@ref) for negative
[`Real`](@ref) arguments.

See also: [`exp2`](@ref), [`log`](@ref), [`ldexp`](@ref), [`ispow2`](@ref).

# Examples
```jldoctest; filter = r"Stacktrace:(\\n \\[[0-9]+\\].*)*"
julia> log2(4)
2.0

julia> log2(10)
3.321928094887362

julia> log2(-2)
ERROR: DomainError with -2.0:
log2 was called with a negative real argument but will only return a complex result if called with a complex argument. Try log2(Complex(x)).
Stacktrace:
 [1] throw_complex_domainerror(f::Symbol, x::Float64) at ./math.jl:31
[...]

julia> log2.(2.0 .^ (-1:1))
3-element Vector{Float64}:
 -1.0
  0.0
  1.0
```
"""
log2(x)

"""
    log10(x)

Compute the logarithm of `x` to base 10.
Throw a [`DomainError`](@ref) for negative [`Real`](@ref) arguments.

See also: [`exp10`](@ref), [`log`](@ref).

# Examples
```jldoctest; filter = r"Stacktrace:(\\n \\[[0-9]+\\].*)*"
julia> log10(100)
2.0

julia> log10(2)
0.3010299956639812

julia> log10(-2)
ERROR: DomainError with -2.0:
log10 was called with a negative real argument but will only return a complex result if called with a complex argument. Try log10(Complex(x)).
Stacktrace:
 [1] throw_complex_domainerror(f::Symbol, x::Float64) at ./math.jl:31
[...]
```
"""
log10(x)

"""
    log1p(x)

Accurate natural logarithm of `1+x`. Throw a [`DomainError`](@ref) for [`Real`](@ref)
arguments less than -1.

# Examples
```jldoctest; filter = r"Stacktrace:(\\n \\[[0-9]+\\].*)*"
julia> log1p(-0.5)
-0.6931471805599453

julia> log1p(0)
0.0

julia> log1p(-2)
ERROR: DomainError with -2.0:
log1p was called with a real argument < -1 but will only return a complex result if called with a complex argument. Try log1p(Complex(x)).
Stacktrace:
 [1] throw_complex_domainerror(::Symbol, ::Float64) at ./math.jl:31
[...]
```
"""
log1p(x)

@inline function sqrt(x::IEEEFloat)
    x < zero(x) && throw_complex_domainerror(:sqrt, x)
    sqrt_llvm(x)
end

"""
    sqrt(x)

Return ``\\sqrt{x}``.

Throw a [`DomainError`](@ref) for negative [`Real`](@ref) arguments.
Use [`Complex`](@ref) negative arguments instead to obtain a [`Complex`](@ref) result.

The prefix operator `√` is equivalent to `sqrt`.

!!! note "Branch cut"
    `sqrt` has a branch cut along the negative real axis; `-0.0im` is taken
    to be below the axis.

See also [`cbrt`](@ref), [`fourthroot`](@ref), [`hypot`](@ref).

# Examples
```jldoctest; filter = r"Stacktrace:(\\n \\[[0-9]+\\].*)*"
julia> sqrt(big(81))
9.0

julia> sqrt(big(-81))
ERROR: DomainError with -81.0:
NaN result for non-NaN input.
Stacktrace:
 [1] sqrt(::BigFloat) at ./mpfr.jl:501
[...]

julia> sqrt(big(complex(-81)))
0.0 + 9.0im

julia> sqrt(-81 - 0.0im)  # -0.0im is below the branch cut
0.0 - 9.0im

julia> .√(1:4)
4-element Vector{Float64}:
 1.0
 1.4142135623730951
 1.7320508075688772
 2.0
```
"""
sqrt(x)

"""
    fourthroot(x)

Return the fourth root of `x`.

See also [`cbrt`](@ref), [`sqrt`](@ref).
"""
fourthroot(x::Number) = sqrt(sqrt(x))

"""
    hypot(x, y)

Compute the hypotenuse ``\\sqrt{|x|^2+|y|^2}`` avoiding overflow and underflow.

This code is an implementation of the algorithm described in:
[*An Improved Algorithm for `hypot(a,b)`* by Carlos F. Borges](https://arxiv.org/abs/1904.09481)

    hypot(x...)

Compute the hypotenuse ``\\sqrt{\\sum |x_i|^2}`` avoiding overflow and underflow.

See also `norm` in the [`LinearAlgebra`](@ref man-linalg) standard library.

# Examples
```jldoctest; filter = r"Stacktrace:(\\n \\[[0-9]+\\].*)*"
julia> a = Int64(10)^10;

julia> hypot(a, a)
1.4142135623730951e10

julia> √(a^2 + a^2) # a^2 overflows
ERROR: DomainError with -2.914184810805068e18:
sqrt was called with a negative real argument but will only return a complex result if called with a complex argument. Try sqrt(Complex(x)).
Stacktrace:
[...]

julia> hypot(3, 4im)
5.0

julia> hypot(-5.7)
5.7

julia> hypot(3, 4im, 12.0)
13.0

julia> using LinearAlgebra

julia> norm([a, a, a, a]) == hypot(a, a, a, a)
true
```
"""
hypot(x::Number) = abs(float(x))
hypot(x::Number, y::Number) = _hypot(float.(promote(x, y))...)
hypot(x::Number, y::Number, xs::Number...) = _hypot(float.(promote(x, y, xs...)))
function _hypot(x, y)
    # preserves unit
    axu = abs(x)
    ayu = abs(y)

    # unitless
    ax = axu / oneunit(axu)
    ay = ayu / oneunit(ayu)

    # Return Inf if either or both inputs is Inf (Compliance with IEEE754)
    if isinf(ax) || isinf(ay)
        return typeof(axu)(Inf)
    end

    # Order the operands
    if ay > ax
        axu = ayu
        ax, ay = ay, ax
    end

    # Widely varying operands
    if ay <= ax*sqrt(eps(typeof(ax))/2)  #Note: This also gets ay == 0
        return axu
    end

    # Operands do not vary widely
    scale = eps(typeof(ax))*sqrt(floatmin(ax))  #Rescaling constant
    if ax > sqrt(floatmax(ax)/2)
        ax = ax*scale
        ay = ay*scale
        scale = inv(scale)
    elseif ay < sqrt(floatmin(ax))
        ax = ax/scale
        ay = ay/scale
    else
        scale = oneunit(scale)
    end
    h = sqrt(muladd(ax, ax, ay*ay))
    # This branch is correctly rounded but requires a native hardware fma.
    if Core.Intrinsics.have_fma(typeof(h))
        hsquared = h*h
        axsquared = ax*ax
        h -= (fma(-ay, ay, hsquared-axsquared) + fma(h, h,-hsquared) - fma(ax, ax, -axsquared))/(2*h)
    # This branch is within one ulp of correctly rounded.
    else
        if h <= 2*ay
            delta = h-ay
            h -= muladd(delta, delta-2*(ax-ay), ax*(2*delta - ax))/(2*h)
        else
            delta = h-ax
            h -= muladd(delta, delta, muladd(ay, (4*delta - ay), 2*delta*(ax - 2*ay)))/(2*h)
        end
    end
    return h*scale*oneunit(axu)
end
# @assume_effects :nothrow: isinf guards handle Inf inputs; muladd(x,x,y*y) is always ≥ 0
# so the sqrt call never throws.
@assume_effects :nothrow @inline function _hypot(x::Float32, y::Float32)
    if isinf(x) || isinf(y)
        return Inf32
    end
    _x, _y = Float64(x), Float64(y)
    return Float32(sqrt(muladd(_x, _x, _y*_y)))
end
@assume_effects :nothrow @inline function _hypot(x::Float16, y::Float16)
    if isinf(x) || isinf(y)
        return Inf16
    end
    _x, _y = Float32(x), Float32(y)
    return Float16(sqrt(muladd(_x, _x, _y*_y)))
end
_hypot(x::ComplexF16, y::ComplexF16) = Float16(_hypot(ComplexF32(x), ComplexF32(y)))

function _hypot(x::NTuple{N,<:Number}) where {N}
    maxabs = maximum(abs, x)
    if isnan(maxabs) && any(isinf, x)
        return typeof(maxabs)(Inf)
    elseif (iszero(maxabs) || isinf(maxabs))
        return maxabs
    else
        return maxabs * sqrt(sum(y -> abs2(y / maxabs), x))
    end
end

function _hypot(x::NTuple{N,<:IEEEFloat}) where {N}
    T = eltype(x)
    infT = convert(T, Inf)
    x = abs.(x) # doesn't change result but enables computational shortcuts
    # note: any() was causing this to not inline for N=3 but mapreduce() was not
    mapreduce(==(infT), |, x) && return infT # return Inf even if an argument is NaN
    maxabs = reinterpret(T, maximum(z -> reinterpret(Signed, z), x)) # for abs(::IEEEFloat) values, a ::BitInteger cast does not change the result
    maxabs > zero(T) || return maxabs # catch NaN before the @fastmath below, but also shortcut 0 since we can (remove if no more @fastmath below)
    scale,invscale = scaleinv(maxabs)
     # @fastmath(+) to allow reassociation (see #48129)
    add_fast(x, y) = Core.Intrinsics.add_float_fast(x, y) # @fastmath is not available during bootstrap
    return scale * sqrt(mapreduce(y -> abs2(y * invscale), add_fast, x))
end

atan(y::Real, x::Real) = atan(promote(float(y),float(x))...)
atan(y::T, x::T) where {T<:AbstractFloat} = Base.no_op_err("atan", T)

_isless(x::T, y::T) where {T<:AbstractFloat} = (x < y) || (signbit(x) > signbit(y))
min(x::T, y::T) where {T<:AbstractFloat} = isnan(x) || ~isnan(y) && _isless(x, y) ? x : y
max(x::T, y::T) where {T<:AbstractFloat} = isnan(x) || ~isnan(y) && _isless(y, x) ? x : y
minmax(x::T, y::T) where {T<:AbstractFloat} = min(x, y), max(x, y)

min(x::T, y::T) where {T<:IEEEFloat} = min_float(x, y)
max(x::T, y::T) where {T<:IEEEFloat} = max_float(x, y)

"""
    ldexp(x, n)

Compute ``x \\times 2^n``.

See also [`frexp`](@ref), [`exponent`](@ref).

# Examples
```jldoctest
julia> ldexp(5.0, 2)
20.0
```
"""
function ldexp(x::T, e::Integer) where T<:IEEEFloat
    xu = reinterpret(Unsigned, x)
    xs = xu & ~sign_mask(T)
    xs >= exponent_mask(T) && return x # NaN or Inf
    k = (xs >> significand_bits(T)) % Int
    if k == 0 # x is subnormal
        xs == 0 && return x # +-0
        m = leading_zeros(xs) - exponent_bits(T)
        ys = xs << unsigned(m)
        xu = ys | (xu & sign_mask(T))
        k = 1 - m
        # underflow, otherwise may have integer underflow in the following n + k
        e < -50000 && return flipsign(T(0.0), x)
    end
    # For cases where e of an Integer larger than Int make sure we properly
    # overflow/underflow; this is optimized away otherwise.
    if e > typemax(Int)
        return flipsign(T(Inf), x)
    elseif e < typemin(Int)
        return flipsign(T(0.0), x)
    end
    n = e % Int
    k = k +% n
    # overflow, if k is larger than maximum possible exponent
    if k >= exponent_raw_max(T)
        return flipsign(T(Inf), x)
    end
    if k > 0 # normal case
        xu = (xu & ~exponent_mask(T)) | (rem(k, uinttype(T)) << significand_bits(T))
        return reinterpret(T, xu)
    else # subnormal case
        if k <= -significand_bits(T) # underflow
            # overflow, for the case of integer overflow in n + k
            e > 50000 && return flipsign(T(Inf), x)
            return flipsign(T(0.0), x)
        end
        k += significand_bits(T)
        # z = T(2.0) ^ (-significand_bits(T))
        z = reinterpret(T, rem(exponent_bias(T)-significand_bits(T), uinttype(T)) << significand_bits(T))
        xu = (xu & ~exponent_mask(T)) | (rem(k, uinttype(T)) << significand_bits(T))
        return z*reinterpret(T, xu)
    end
end
ldexp(x::Float16, q::Integer) = Float16(ldexp(Float32(x), q))

"""
    exponent(x::Real)::Int

Return the largest integer `y` such that `2^y ≤ abs(x)`.
For a normalized floating-point number `x`, this corresponds to the exponent of `x`.

Throws a `DomainError` when `x` is zero, infinite, or [`NaN`](@ref).
For any other non-subnormal floating-point number `x`, this corresponds to the exponent bits of `x`.

See also [`signbit`](@ref), [`significand`](@ref), [`frexp`](@ref), [`issubnormal`](@ref), [`log2`](@ref), [`ldexp`](@ref).
# Examples
```jldoctest
julia> exponent(8)
3

julia> exponent(6.5)
2

julia> exponent(-1//4)
-2

julia> exponent(3.142e-4)
-12

julia> exponent(floatmin(Float32)), exponent(nextfloat(0.0f0))
(-126, -149)

julia> exponent(0.0)
ERROR: DomainError with 0.0:
Cannot be ±0.0.
[...]
```
"""
function exponent(x::T) where T<:IEEEFloat
    @noinline throw1(x) = throw(DomainError(x, "Cannot be NaN or Inf."))
    @noinline throw2(x) = throw(DomainError(x, "Cannot be ±0.0."))
    xs = reinterpret(Unsigned, x) & ~sign_mask(T)
    xs >= exponent_mask(T) && throw1(x)
    # use `% Int` instead of `Int(...)` to preserve `:nothrow` (the shifted value
    # always fits in `exponent_bits(T)` bits, well below `typemax(Int)`)
    k = (xs >> significand_bits(T)) % Int
    if k == 0 # x is subnormal
        xs == 0 && throw2(x)
        m = leading_zeros(xs) - exponent_bits(T)
        k = 1 - m
    end
    return k - exponent_bias(T)
end

# Like exponent, but assumes the nothrow precondition. For
# internal use only. Could be written as
# @assume_effects :nothrow exponent()
# but currently this form is easier on the compiler.
function _exponent_finite_nonzero(x::T) where T<:IEEEFloat
    # @precond :nothrow !isnan(x) && !isinf(x) && !iszero(x)
    xs = reinterpret(Unsigned, x) & ~sign_mask(T)
    k = rem(xs >> significand_bits(T), Int)
    if k == 0 # x is subnormal
        m = leading_zeros(xs) - exponent_bits(T)
        k = 1 - m
    end
    return k - exponent_bias(T)
end

function _ilog2_step(y::T, d::T, s) where {T<:Integer}
    if (y >> s) >= d
        y, n = _ilog2_step(y, d*d, s+s)
    else
        n = 0
    end
    if y >= d
        y >>= s
        n = Base.checked_add(n, s)
    end
    return y, n
end

function exponent(x::Integer)
    iszero(x) && throw(DomainError(x, "cannot be zero"))
    ux = Base.uabs(x)
    _, n = _ilog2_step(ux, one(ux) + one(ux), 1)
    return n
end

function exponent(x::Base.BitInteger)
    iszero(x) && throw(DomainError(x, "cannot be zero"))
    ux = Base.uabs(x)
    return 8sizeof(ux) - leading_zeros(ux) - 1
end

"""
    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.

See also [`frexp`](@ref), [`exponent`](@ref).

# Examples
```jldoctest
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)
```
"""
function significand(x::T) where T<:IEEEFloat
    xu = reinterpret(Unsigned, x)
    xs = xu & ~sign_mask(T)
    xs >= exponent_mask(T) && return x # NaN or Inf
    if xs <= (~exponent_mask(T) & ~sign_mask(T)) # x is subnormal
        xs == 0 && return x # +-0
        m = unsigned(leading_zeros(xs) - exponent_bits(T))
        xs <<= m
        xu = xs | (xu & sign_mask(T))
    end
    xu = (xu & ~exponent_mask(T)) | exponent_one(T)
    return reinterpret(T, xu)
end

"""
    frexp(val)

Return `(x,exp)` such that `x` has a magnitude in the interval ``[1/2, 1)`` or 0,
and `val` is equal to ``x \\times 2^{exp}``.

See also [`significand`](@ref), [`exponent`](@ref), [`ldexp`](@ref).

# Examples
```jldoctest
julia> frexp(6.0)
(0.75, 3)

julia> significand(6.0), exponent(6.0)  # interval [1, 2) instead
(1.5, 2)

julia> frexp(0.0), frexp(NaN), frexp(-Inf)  # exponent would give an error
((0.0, 0), (NaN, 0), (-Inf, 0))
```
"""
function frexp(x::T) where T<:IEEEFloat
    xu = reinterpret(Unsigned, x)
    xs = xu & ~sign_mask(T)
    xs >= exponent_mask(T) && return x, 0 # NaN or Inf
    # use `% Int` instead of `Int(...)` to preserve `:nothrow` (after masking the sign
    # bit, xs >> significand_bits(T) is at most 2^exponent_bits(T)-1, which always fits in Int)
    k = (xs >> significand_bits(T)) % Int
    if k == 0 # x is subnormal
        xs == 0 && return x, 0 # +-0
        m = leading_zeros(xs) - exponent_bits(T)
        xs <<= unsigned(m)
        xu = xs | (xu & sign_mask(T))
        k = 1 - m
    end
    k -= (exponent_bias(T) - 1)
    xu = (xu & ~exponent_mask(T)) | exponent_half(T)
    return reinterpret(T, xu), k
end

"""
    $(@__MODULE__).scaleinv(x)

Compute `(scale, invscale)` where `scale` and `invscale` are non-subnormal
(https://en.wikipedia.org/wiki/Subnormal_number) finite powers of two such that
`scale * invscale == 1` and `scale` is roughly on the order of `abs(x)`.
Inf, NaN, and zero inputs also result in finite nonzero outputs.
These values are useful to scale computations to prevent overflow and underflow
without round-off errors or division.

UNSTABLE DETAIL: For `x isa IEEEFLoat`, `scale` is chosen to be the
`prevpow(2,abs(x))` when possible, but is never less than floatmin(x) or greater
than inv(floatmin(x)). `Inf` and `NaN` resolve to `inv(floatmin(x))`. This
behavior is subject to change.

# Examples
```jldoctest
julia> $(@__MODULE__).scaleinv(7.5)
(4.0, 0.25)
```
"""
function scaleinv(x::T) where T<:IEEEFloat
    # by removing the sign and significand and restricting values to a limited range,
    # we can invert a number using bit-twiddling instead of division
    U = uinttype(T)
    umin = reinterpret(U, floatmin(T))
    umax = reinterpret(U, inv(floatmin(T)))
    emask = exponent_mask(T) # used to strip sign and significand
    u = clamp(reinterpret(U, x) & emask, umin, umax)
    scale = reinterpret(T, u)
    invscale = reinterpret(T, umin + umax - u) # inv(scale)
    return scale, invscale
end

# NOTE: This `rem` method is adapted from the msun `remainder` and `remainderf`
# functions, which are under the following license:
#
# Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
#
# Developed at SunSoft, a Sun Microsystems, Inc. business.
# Permission to use, copy, modify, and distribute this
# software is freely granted, provided that this notice
# is preserved.
function rem(x::T, p::T, ::RoundingMode{:Nearest}) where T<:IEEEFloat
    (iszero(p) || !isfinite(x) || isnan(p)) && return T(NaN)
    x == p && return copysign(zero(T), x)
    oldx = x
    x = abs(rem(x, 2p))  # 2p may overflow but that's okay
    p = abs(p)
    if p < 2 * floatmin(T)  # Check whether dividing p by 2 will underflow
        if 2x > p
            x -= p
            if 2x >= p
                x -= p
            end
        end
    else
        p_half = p / 2
        if x > p_half
            x -= p
            if x >= p_half
                x -= p
            end
        end
    end
    return flipsign(x, oldx)
end


"""
    modf(x)

Return a tuple `(fpart, ipart)` of the fractional and integral parts of a number. Both parts
have the same sign as the argument.

# Examples
```jldoctest
julia> modf(3.5)
(0.5, 3.0)

julia> modf(-3.5)
(-0.5, -3.0)
```
"""
modf(x) = isinf(x) ? (flipsign(zero(x), x), x) : (rem(x, one(x)), trunc(x))

function modf(x::T) where T<:IEEEFloat
    isinf(x) && return (copysign(zero(T), x), x)
    ix = trunc(x)
    rx = copysign(x - ix, x)
    return (rx, ix)
end



## rem2pi-related calculations ##

function add22condh(xh::Float64, xl::Float64, yh::Float64, yl::Float64)
    # This algorithm, due to Dekker, computes the sum of two
    # double-double numbers and returns the high double. References:
    # [1] http://www.digizeitschriften.de/en/dms/img/?PID=GDZPPN001170007
    # [2] https://doi.org/10.1007/BF01397083
    r = xh+yh
    s = (abs(xh) > abs(yh)) ? (xh-r+yh+yl+xl) : (yh-r+xh+xl+yl)
    zh = r+s
    return zh
end

"""
    rem2pi(x, r::RoundingMode)

Compute the remainder of `x` after integer division by `2π`, with the quotient rounded
according to the rounding mode `r`. In other words, the quantity

    x - 2π*round(x/(2π),r)

without any intermediate rounding. This internally uses a high precision approximation of
2π, and so will give a more accurate result than `rem(x,2π,r)`

- if `r == RoundNearest`, then the result is in the interval ``[-π, π]``. This will generally
  be the most accurate result. See also [`RoundNearest`](@ref).

- if `r == RoundToZero`, then the result is in the interval ``[0, 2π]`` if `x` is positive,.
  or ``[-2π, 0]`` otherwise. See also [`RoundToZero`](@ref).

- if `r == RoundDown`, then the result is in the interval ``[0, 2π]``.
  See also [`RoundDown`](@ref).
- if `r == RoundUp`, then the result is in the interval ``[-2π, 0]``.
  See also [`RoundUp`](@ref).

# Examples
```jldoctest
julia> rem2pi(7pi/4, RoundNearest)
-0.7853981633974485

julia> rem2pi(7pi/4, RoundDown)
5.497787143782138
```
"""
function rem2pi end

"""
    mod2pi(x)

Modulus after division by `2π`, returning in the range ``[0,2π)``.

This function computes a floating point representation of the modulus after division by
numerically exact `2π`, and is therefore not exactly the same as `mod(x,2π)`, which would
compute the modulus of `x` relative to division by the floating-point number `2π`.

!!! note
    Depending on the format of the input value, the closest representable value to 2π may
    be less than 2π. For example, the expression `mod2pi(2π)` will not return `0`, because
    the intermediate value of `2*π` is a `Float64` and `2*Float64(π) < 2*big(π)`. See
    [`rem2pi`](@ref) for more refined control of this behavior.

# Examples
```jldoctest
julia> mod2pi(9*pi/4)
0.7853981633974481
```
"""
mod2pi(x) = rem2pi(x,RoundDown)

# generic fallback; for number types, promotion.jl does promotion

"""
    muladd(x, y, z)

Combined multiply-add: computes `x*y+z`, but allowing the add and multiply to be merged
with each other or with surrounding operations for performance.
For example, this may be implemented as an [`fma`](@ref) if the hardware supports it
efficiently.
The result can be different on different machines and can also be different on the same machine
due to constant propagation or other optimizations.
See [`fma`](@ref).

# Examples
```jldoctest
julia> muladd(3, 2, 1)
7

julia> 3 * 2 + 1
7
```
"""
muladd(x,y,z) = x*y+z


# helper functions for Libm functionality

"""
    highword(x)

Return the high word of `x` as a `UInt32`.
"""
@inline highword(x::Float64) = highword(reinterpret(UInt64, x))
@inline highword(x::UInt64)  = (x >>> 32) % UInt32
@inline highword(x::Float32) = reinterpret(UInt32, x)

@inline fromhighword(::Type{Float64}, u::UInt32) = reinterpret(Float64, UInt64(u) << 32)
@inline fromhighword(::Type{Float32}, u::UInt32) = reinterpret(Float32, u)


"""
    poshighword(x)

Return positive part of the high word of `x` as a `UInt32`.
"""
@inline poshighword(x::Float64) = poshighword(reinterpret(UInt64, x))
@inline poshighword(x::UInt64)  = highword(x) & 0x7fffffff
@inline poshighword(x::Float32) = highword(x) & 0x7fffffff

# More special functions
include("special/cbrt.jl")
include("special/exp.jl")
include("special/hyperbolic.jl")
include("special/trig.jl")
include("special/rem_pio2.jl")
include("special/rem2pi.jl")
include("special/log.jl")
include("special/pow.jl")



# Float16 definitions

for func in (:sin,:cos,:tan,:asin,:acos,:atan,:cosh,:tanh,:asinh,:acosh,
             :atanh,:log,:log2,:log10,:log1p)
    @eval begin
        $func(a::Float16) = Float16($func(Float32(a)))
        $func(a::ComplexF16) = ComplexF16($func(ComplexF32(a)))
    end
end

for func in (:exp,:exp2,:exp10,:sinh)
     @eval $func(a::ComplexF16) = ComplexF16($func(ComplexF32(a)))
end


atan(a::Float16,b::Float16) = Float16(atan(Float32(a),Float32(b)))
sincos(a::Float16) = Float16.(sincos(Float32(a)))

for f in (:sin, :cos, :tan, :asin, :atan, :acos,
          :sinh, :cosh, :tanh, :asinh, :acosh, :atanh,
          :exp, :exp2, :exp10, :expm1, :log, :log2, :log10, :log1p,
          :exponent, :sqrt, :cbrt, :sinpi, :cospi, :sincospi, :tanpi)
    @eval function ($f)(x::Real)
        xf = float(x)
        xf isa typeof(x) && throw(MethodError($f, (x,)))
        return ($f)(xf)
    end
    @eval $(f)(::Missing) = missing
end

for f in (:atan, :hypot, :log)
    @eval $(f)(::Missing, ::Missing) = missing
    @eval $(f)(::Number, ::Missing) = missing
    @eval $(f)(::Missing, ::Number) = missing
end

exp2(x::AbstractFloat) = 2^x
exp10(x::AbstractFloat) = 10^x
fourthroot(::Missing) = missing

end # module
