diff --git a/swift/Sources/QRCodeGenerator/BitBuffer.swift b/swift/Sources/QRCodeGenerator/BitBuffer.swift
index b710178..ea648e2 100644
--- a/swift/Sources/QRCodeGenerator/BitBuffer.swift
+++ b/swift/Sources/QRCodeGenerator/BitBuffer.swift
@@ -33,7 +33,7 @@ public struct BitBuffer {
 	/// Appends the given number of low-order bits of the given value to this buffer.
 	/// 
 	/// Requires len &#x2264; 31 and val &lt; 2<sup>len</sup>.
-	public mutating func writeBits(_ value: UInt32, _ length: Int) {
+	public mutating func appendBits(_ value: UInt32, _ length: Int) {
 		assert(length <= 31 && (value >> length) == 0, "Value out of range")
 		bits.append((0..<length).reversed().map { getBit(value, $0) })
 	}
diff --git a/swift/Sources/QRCodeGenerator/QRSegment.swift b/swift/Sources/QRCodeGenerator/QRSegment.swift
new file mode 100644
index 0000000..12ed527
--- /dev/null
+++ b/swift/Sources/QRCodeGenerator/QRSegment.swift
@@ -0,0 +1,148 @@
+/* 
+ * QR Code generator library (Swift)
+ * 
+ * Copyright (c) Project Nayuki. (MIT License)
+ * https://www.nayuki.io/page/qr-code-generator-library
+ * 
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to
+ * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+ * the Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ * - The above copyright notice and this permission notice shall be included in
+ *   all copies or substantial portions of the Software.
+ * - The Software is provided "as is", without warranty of any kind, express or
+ *   implied, including but not limited to the warranties of merchantability,
+ *   fitness for a particular purpose and noninfringement. In no event shall the
+ *   authors or copyright holders be liable for any claim, damages or other
+ *   liability, whether in an action of contract, tort or otherwise, arising from,
+ *   out of or in connection with the Software or the use or other dealings in the
+ *   Software.
+ */
+
+/*---- QrSegment functionality ----*/
+
+/// A segment of character/binary/control data in a QR Code symbol.
+/// 
+/// Instances of this struct are immutable.
+/// 
+/// The mid-level way to create a segment is to take the payload data
+/// and call a static factory function such as `QrSegment::make_numeric()`.
+/// The low-level way to create a segment is to custom-make the bit buffer
+/// and call the `QrSegment::new()` constructor with appropriate values.
+/// 
+/// This segment struct imposes no length restrictions, but QR Codes have restrictions.
+/// Even in the most favorable conditions, a QR Code can only hold 7089 characters of data.
+/// Any segment longer than this is meaningless for the purpose of generating QR Codes.
+public struct QRSegment: Hashable {
+	/// The mode indicator of this segment.
+	public let mode: Mode
+	/// The length of this segment's unencoded data. Measured in characters for
+	/// numeric/alphanumeric/kanji mode, bytes for byte mode, and 0 for ECI mode.
+	/// Not the same as the data's bit length.
+	public let numChars: UInt
+	/// The data bits of this segment.
+	public let data: [Bool]
+	
+	/*---- Static factory functions (mid level) ----*/
+
+	/// Returns a segment representing the given binary data encoded in byte mode.
+	/// 
+	/// All input byte slices are acceptable.
+	/// 
+	/// Any text string can be converted to UTF-8 bytes and encoded as a byte mode segment.
+	public static func makeBytes(data: [UInt8]) -> Self {
+		var bb = BitBuffer([])
+		for b in data {
+			bb.appendBits(UInt32(b), 8)
+		}
+		return QRSegment(mode: .byte, numChars: data.count, data: bb.bits)
+	}
+	
+	/// Returns a segment representing the given string of decimal digits encoded in numeric mode.
+	/// 
+	/// Panics if the string contains non-digit characters.
+	public static func makeNumeric(text: [Character]) -> Self {
+		var bb = BitBuffer([])
+		var accumData: UInt32 = 0
+		var accumCount: UInt8 = 0
+		for c in text {
+			assert(c.isNumber && c.isASCII, "String contains non-numeric characters")
+			accumData = accumData * 10 + (UInt32(c.asciiValue!) - UInt32("0".asciiValue!))
+			accumCount += 1
+			if accumCount == 3 {
+				bb.appendBits(accumData, 10)
+				accumData = 0
+				accumCount = 0
+			}
+		}
+		if accumCount > 0 { // 1 or 2 digits remaining
+			bb.appendBits(accumData, accumCount * 3 + 1)
+		}
+		return QRSegment(mode: .numeric, numChars: text.count, data: bb.bits)
+	}
+	
+	/// Returns a segment representing the given text string encoded in alphanumeric mode.
+	/// 
+	/// The characters allowed are: 0 to 9, A to Z (uppercase only), space,
+	/// dollar, percent, asterisk, plus, hyphen, period, slash, colon.
+	/// 
+	/// Panics if the string contains non-encodable characters.
+	public static func makeAlphanumeric(text: [Character]) -> Self {
+		var bb = BitBuffer([])
+		var accumData: UInt32 = 0
+		var accumCount: UInt32 = 0
+		for c in text {
+			guard let i = alphanumericCharset.firstIndex(of: c) else {
+				fatalError("String contains unencodable characters in alphanumeric mode")
+			}
+			accumData = accumData * 45 + UInt32(i)
+			accumCount += 1
+			if accumCount == 2 {
+				bb.appendBits(accumData, 11)
+				accumData = 0
+				accumCount = 0
+			}
+		}
+		if accumCount > 0 { // 1 character remaining
+			bb.appendBits(accumData, 6)
+		}
+		return QRSegment(mode: .alphanumeric, numChars: text.count, data: bb.bits)
+	}
+	
+	/// Returns a list of zero or more segments to represent the given Unicode text string.
+	/// 
+	/// The result may use various segment modes and switch
+	/// modes to optimize the length of the bit stream.
+	public static func makeSegments(text: [Character]) -> Self {
+		if text.isEmpty {
+			return []
+		} else if QRSegment.isNumeric(text) {
+			return [QRSegment.makeNumeric(text)]
+		} else if QRSegment.isAlphanumeric(text) {
+			return [QRSegment.makeAlphanumeric(text)]
+		} else {
+			let s = String(text)
+			return [QRSegment.makeBytes([UInt8](s.data(using: .utf8)!))]
+		}
+	}
+	
+	/// Returns a segment representing an Extended Channel Interpretation
+	/// (ECI) designator with the given assignment value.
+	public static func makeECI(assignVal: UInt32) -> Self {
+		var bb = BitBuffer([])
+		if assignVal < (1 << 7) {
+			bb.appendBits(assignVal, 8)
+		} else if assignVal < (1 << 14) {
+			bb.appendBits(2, 2)
+			bb.appendBits(assignVal, 14)
+		} else if assignVal < 1_000_000 {
+			bb.appendBits(6, 3)
+			bb.appendBits(assignVal, 21)
+		} else {
+			fatalError("ECI assignment value out of range")
+		}
+		return QRSegment(mode: .eci, numChars: 0, data: bb.bits)
+	}
+}