50 lines
1.6 KiB
Swift
50 lines
1.6 KiB
Swift
//
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// Copyright (c) 2018 Open Whisper Systems. All rights reserved.
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//
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import Foundation
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public extension String {
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// Truncates string to be less than or equal to byteCount, while ensuring we never truncate partial characters for multibyte characters.
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public func truncated(toByteCount byteCount: UInt) -> String? {
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var lowerBoundCharCount = 0
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var upperBoundCharCount = self.count
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while (lowerBoundCharCount < upperBoundCharCount) {
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guard let upperBoundData = self.prefix(upperBoundCharCount).data(using: .utf8) else {
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owsFail("in \(#function) upperBoundData was unexpectedly nil")
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return nil
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}
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if upperBoundData.count <= byteCount {
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break
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}
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// converge
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if upperBoundCharCount - lowerBoundCharCount == 1 {
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upperBoundCharCount = lowerBoundCharCount
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break
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}
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let midpointCharCount = (lowerBoundCharCount + upperBoundCharCount) / 2
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let midpointString = self.prefix(midpointCharCount)
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guard let midpointData = midpointString.data(using: .utf8) else {
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owsFail("in \(#function) midpointData was unexpectedly nil")
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return nil
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}
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let midpointByteCount = midpointData.count
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if midpointByteCount < byteCount {
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lowerBoundCharCount = midpointCharCount
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} else {
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upperBoundCharCount = midpointCharCount
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}
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}
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return String(self.prefix(upperBoundCharCount))
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}
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}
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