rounded(_:)

使用指定的舍入規則將該值取整。

程式碼示例

let nums = [3.0, 3.001, 3.5, 3.999, -3.0, -3.001, -3.5, -3.999]
let rules = [FloatingPointRoundingRule.awayFromZero, .down, .toNearestOrAwayFromZero, .toNearestOrEven, .towardZero, .up]

for rule in rules {
    print("========\(rule)========")
    for num in nums {
        let
 
 value = num.rounded(rule)
        print("Rule: \(rule), Source: \(num), Value: \(value)")
    }
}

/*
========awayFromZero========
Source: 3.0, Value: 3.0
Source: 3.001, Value: 4.0
Source: 3.5, Value: 4.0
Source: 3.999, Value: 4.0
Source: -3.0, Value: -3.0
Source: -3.001, Value: -4.0
Source: -3.5, Value: -4.0
Source: -3.999, Value: -4.0
========down========
Source: 3.0, Value: 3.0
Source: 3.001, Value: 3.0
Source: 3.5, Value: 3.0
Source: 3.999, Value: 3.0
Source: -3.0, Value: -3.0
Source: -3.001, Value: -4.0
Source: -3.5, Value: -4.0
Source: -3.999, Value: -4.0
========toNearestOrAwayFromZero========
Source: 3.0, Value: 3.0
Source: 3.001, Value: 3.0
Source: 3.5, Value: 4.0
Source: 3.999, Value: 4.0
Source: -3.0, Value: -3.0
Source: -3.001, Value: -3.0
Source: -3.5, Value: -4.0
Source: -3.999, Value: -4.0
========toNearestOrEven========
Source: 3.0, Value: 3.0
Source: 3.001, Value: 3.0
Source: 3.5, Value: 4.0
Source: 3.999, Value: 4.0
Source: -3.0, Value: -3.0
Source: -3.001, Value: -3.0
Source: -3.5, Value: -4.0
Source: -3.999, Value: -4.0
========towardZero========
Source: 3.0, Value: 3.0
Source: 3.001, Value: 3.0
Source: 3.5, Value: 3.0
Source: 3.999, Value: 3.0
Source: -3.0, Value: -3.0
Source: -3.001, Value: -3.0
Source: -3.5, Value: -3.0
Source: -3.999, Value: -3.0
========up========
Source: 3.0, Value: 3.0
Source: 3.001, Value: 4.0
Source: 3.5, Value: 4.0
Source: 3.999, Value: 4.0
Source: -3.0, Value: -3.0
Source: -3.001, Value: -3.0
Source: -3.5, Value: -3.0
Source: -3.999, Value: -3.0
 */
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總結

• awayFromZero: 四捨五入到最接近的值，返回值大於或等於源的大小（該規則比較的是絕對值）

let num = 3.5
num.rounded(.awayFromZero) // 4

let num2 = -3.5
num2.rounded(.awayFromZero) //-4
//可以看出 -4是小於-3.5的，所以它的規則說返回值大於或等於源指的是兩值的絕對值的比較
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• down: 四捨五入到最接近的值，返回值小於於或等於源的大小（改規則不是比較的絕對值）
• toNearestOrAwayFromZero: 四捨五入到最接近的值;如果兩個值相等接近，則選擇幅度較大的值
• toNearestOrEven:四捨五入到最接近的值;如果兩個值相等接近，則選擇偶數。

let num = 3.5
// 這是3與4同等接近，選擇偶數4
num.rounded(.toNearestOrEven)  // 4
let num2 = 4.5
// 這是4與5同等接近，選擇偶數4
num2.rounded(.toNearestOrEven)  // 4
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• towardZero: 四捨五入到最接近的值，返回值小於於或等於源的大小；通過上面的例子可以看出它是忽略負號的；與awayFromZero對應
• up: 四捨五入到最接近的值，返回值大於或等於源的大小；不忽略負號；與up對應

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