Round Number

26 Aug 2017 by 晓晨

更新：这个方法更好。https://stackoverflow.com/a/41488326

原文中还给出了具体的实现和传统方法的对应。

The FloatingPoint protocol (to which e.g. Double and Float conforms) blueprints the rounded(_:) method

func rounded(_ rule: FloatingPointRoundingRule) -> Self

Where FloatingPointRoundingRule is an enum enumerating a number of different rounding rules:

case awayFromZero

Round to the closest allowed value whose magnitude is greater than or equal to that of the source.

case down

Round to the closest allowed value that is less than or equal to the source.

case toNearestOrAwayFromZero

Round to the closest allowed value; if two values are equally close, the one with greater magnitude is chosen.

case toNearestOrEven

Round to the closest allowed value; if two values are equally close, the even one is chosen.

case towardZero

Round to the closest allowed value whose magnitude is less than or equal to that of the source.

case up

Round to the closest allowed value that is greater than or equal to the source.

其中，toNearestOrAwayFromZero 是远离 0 的四舍五入，toNearestOrEven 的类似，但不是完全的四舍五入，而是尽可能地靠向偶数，具体使用场景不清楚。其它几个都是不同方向的取整。

旧文分割线

注意：

• 库

• 参数和返回值

• 对于负数

四舍五入

round

import Darwin.C.math
// included by UIKit

//public func roundf(_: Float) -> Float
//public func round(_: Double) -> Double
//
//public func lroundf(_: Float) -> Int
//public func lround(_: Double) -> Int
//
//public func llroundf(_: Float) -> Int64
//public func llround(_: Double) -> Int64

https://github.com/goxcif/playgrounds/tree/master/round-number.playground