将代码从Objective-C转换为Swift后,测试用例失败

Question

我正在以Swift风格进行一些按位操作,这些代码最初是用Objective-C/C编写的.我UnsafeMutablePointer用来说明内存地址的起始索引,并UnsafeMutableBufferPointer用于访问范围内的元素.

您可以在此处访问原始的Objective-C文件.

public init(size: Int) {
    self.size = size
    self.bitsLength = (size + 31) / 32
    self.startIdx = UnsafeMutablePointer<Int32>.alloc(bitsLength * sizeof(Int32))
    self.bits = UnsafeMutableBufferPointer(start: startIdx, count: bitsLength)
}

/**
 * @param from first bit to check
 * @return index of first bit that is set, starting from the given index, or size if none are set
 *  at or beyond its given index
 */
public func nextSet(from: Int) -> Int {
    if from >= size { return size }
    var bitsOffset = from / 32
    var currentBits: Int32 = bits[bitsOffset]
    currentBits &= ~((1 << (from & 0x1F)) - 1).to32
    while currentBits == 0 {
        if ++bitsOffset == bitsLength {
            return size
        }
        currentBits = bits[bitsOffset]
    }
    let result: Int = bitsOffset * 32 + numberOfTrailingZeros(currentBits).toInt
    return result > size ? size : result
}

func numberOfTrailingZeros(i: Int32) -> Int {
    var i = i
    guard i != 0 else { return 32 }
    var n = 31
    var y: Int32
    y = i << 16
    if y != 0 { n = n - 16; i = y }
    y = i << 8
    if y != 0 { n = n - 8; i = y }
    y = i << 4
    if y != 0 { n = n - 4; i = y }
    y = i << 2
    if y != 0 { n = n - 2; i = y }
    return n - Int((UInt((i << 1)) >> 31))
}

测试用例:

func testGetNextSet1() {
    // Passed
    var bits = BitArray(size: 32)
    for i in 0..<bits.size {
        XCTAssertEqual(32, bits.nextSet(i), "\(i)")
    }
    // Failed
    bits = BitArray(size: 34)
    for i in 0..<bits.size {
        XCTAssertEqual(34, bits.nextSet(i), "\(i)")
    }
}

有人可以指导我为什么第二个测试用例失败但是Objective-c版本通过了？

编辑:正如@vacawama所说:如果你将testGetNextSet分成2个测试,两个都通过.

EDIT2:当我运行测试xctool,其通话,并测试BitArray的nextSet()会崩溃而运行.

Answer 1

Objective-C 版本numberOfTrailingZeros：

// Ported from OpenJDK Integer.numberOfTrailingZeros implementation
- (int32_t)numberOfTrailingZeros:(int32_t)i {
    int32_t y;
    if (i == 0) return 32;
    int32_t n = 31;
    y = i <<16; if (y != 0) { n = n -16; i = y; }
    y = i << 8; if (y != 0) { n = n - 8; i = y; }
    y = i << 4; if (y != 0) { n = n - 4; i = y; }
    y = i << 2; if (y != 0) { n = n - 2; i = y; }
    return n - (int32_t)((uint32_t)(i << 1) >> 31);
}

翻译时numberOfTrailingZeros，您将返回值从 更改Int32为Int。这很好，但是函数的最后一行在翻译时无法正常运行。

在 中numberOfTrailingZeros，替换为：

return n - Int((UInt((i << 1)) >> 31))

有了这个：

return n - Int(UInt32(bitPattern: i << 1) >> 31)

强制转换将UInt32删除除低 32 位以外的所有位。由于您正在投射到UInt，因此您没有删除这些位。有必要使用bitPattern来实现这一点。