//===--- MathFunctions.swift ----------------------------------*- swift -*-===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2019 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//

import SwiftShims
%from SwiftMathFunctions import *
%from SwiftFloatingPointTypes import all_floating_point_types

/// A type that has elementary functions available.
///
/// An ["elementary function"][elfn] is a function built up from powers, roots,
/// exponentials, logarithms, trigonometric functions (sin, cos, tan) and
/// their inverses, and the hyperbolic functions (sinh, cosh, tanh) and their
/// inverses.
///
/// Conformance to this protocol means that all of these building blocks are
/// available as static functions on the type.
///
/// ```swift
/// let x: Float = 1
/// let y = Float.sin(x) // 0.84147096
/// ```
///
/// Additional operations, such as `atan2(y:x:)`, `hypot(_:_:)` and some
/// special functions, are provided on the Real protocol, which refines both
/// ElementaryFunctions and FloatingPoint.
///
/// [elfn]: http://en.wikipedia.org/wiki/Elementary_function
public protocol ElementaryFunctions {

%for func in ElementaryFunctions:

  ${func.comment}
  static func ${func.decl("Self")}
%end

  /// `exp(y log(x))` computed without loss of intermediate precision.
  ///
  /// For real types, if `x` is negative the result is NaN, even if `y` has
  /// an integral value. For complex types, there is a branch cut on the
  /// negative real axis.
  static func pow(_ x: Self, _ y: Self) -> Self

  /// `x` raised to the `n`th power.
  static func pow(_ x: Self, _ n: Int) -> Self

  /// The `n`th root of `x`.
  ///
  /// For real types, if `x` is negative and `n` is even, the result is NaN.
  /// For complex types, there is a branch cut along the negative real axis.
  static func root(_ x: Self, _ n: Int) -> Self
}

/// A type that models the real numbers.
///
/// Conformance to this protocol means that all the FloatingPoint operations
/// are available, as well as the ElementaryFunctions, plus the following
/// additional math functions: atan2, erf, erc, hypot, tgamma.
///
/// logGamma and signGamma are also available on non-Windows platforms.
public protocol Real: ElementaryFunctions, FloatingPoint {
%for func in RealFunctions:

  ${func.comment}
  static func ${func.decl("Self")}
%end

  /// `atan(y/x)` with quadrant fixup.
  ///
  /// There is an infinite family of angles whose tangent is `y/x`. `atan2`
  /// selects the representative that is the angle between the vector `(x, y)`
  /// and the real axis in the range [-π, π].
  static func atan2(y: Self, x: Self) -> Self

#if !os(Windows)
  //  lgamma is not available on Windows.
  //  TODO: provide an implementation of lgamma with the stdlib to support
  //  Windows so we can vend a uniform interface.

  /// `log(gamma(x))` computed without undue overflow.
  ///
  /// `log(abs(gamma(x)))` is returned. To get the sign of `gamma(x)` cheaply,
  /// use `signGamma(x)`.
  static func logGamma(_ x: Self) -> Self
#endif
}

extension Real {
#if !os(Windows)
  //  lgamma is not available on Windows; no lgamma means signGamma
  //  is basically useless, so don't bother exposing it.

  /// The sign of `gamma(x)`.
  ///
  /// This function is typically used in conjunction with `logGamma(x)`, which
  /// computes `log(abs(gamma(x)))`, to recover the sign information that is
  /// lost to the absolute value.
  ///
  /// `gamma(x)` has a simple pole at each non-positive integer and an
  /// essential singularity at infinity; we arbitrarily choose to return
  /// `.plus` for the sign in those cases. For all other values, `signGamma(x)`
  /// is `.plus` if `x >= 0` or `trunc(x)` is odd, and `.minus` otherwise.
  @_alwaysEmitIntoClient
  public static func signGamma(_ x: Self) -> FloatingPointSign {
    if x >= 0 { return .plus }
    let trunc = x.rounded(.towardZero)
    // Treat poles as gamma(x) == +inf. This is arbitrary, but we need to
    // pick one sign or the other.
    if x == trunc { return .plus }
    // Result is .minus if trunc is even, .plus otherwise. To figure out if
    // trunc is even or odd, check if trunc/2 is an integer.
    let halfTrunc = trunc/2
    if halfTrunc == halfTrunc.rounded(.towardZero) { return .minus }
    return .plus
  }
#endif
}

%for type in all_floating_point_types():
% if type.bits == 80:
#if (arch(i386) || arch(x86_64)) && !os(Windows)
% end
% Self = type.stdlib_name
extension ${Self}: Real {
% for func in ElementaryFunctions + RealFunctions:

  @_alwaysEmitIntoClient
  public static func ${func.decl(Self)} {
    return ${func.impl(type)}
  }
% end

  @_alwaysEmitIntoClient
  public static func pow(_ x: ${Self}, _ y: ${Self}) -> ${Self} {
    guard x >= 0 else { return .nan }
    return ${Self}(Builtin.int_pow_FPIEEE${type.bits}(x._value, y._value))
  }

  @_alwaysEmitIntoClient
  public static func pow(_ x: ${Self}, _ n: Int) -> ${Self} {
    // TODO: this implementation isn't quite right for n so large that
    // the conversion to `${Self}` rounds. We could also consider using
    // a multiply-chain implementation for small `n`; this would be faster
    // for static `n`, but less accurate on platforms with a good `pow`
    // implementation.
    return ${Self}(Builtin.int_pow_FPIEEE${type.bits}(x._value, ${Self}(n)._value))
  }

  @_alwaysEmitIntoClient
  public static func root(_ x: ${Self}, _ n: Int) -> ${Self} {
    guard x >= 0 || n % 2 != 0 else { return .nan }
    // TODO: this implementation isn't quite right for n so large that
    // the conversion to `${Self}` rounds.
    return ${Self}(signOf: x, magnitudeOf: pow(x, 1/${Self}(n)))
  }

  @_alwaysEmitIntoClient
  public static func atan2(y: ${Self}, x: ${Self}) -> ${Self} {
    return _swift_stdlib_atan2${type.cFuncSuffix}(y, x)
  }

#if !os(Windows)
  @_alwaysEmitIntoClient
  public static func logGamma(_ x: ${Self}) -> ${Self} {
    return _swift_stdlib_lgamma${type.cFuncSuffix}(x)
  }
#endif
}
% if type.bits == 80:
#endif
% end
%end