Tweaked code and comment in QrCode.encodeSegments() in all language versions.

c/qrcodegen.c

@@ -914,7 +914,6 @@ bool qrcodegen_encodeSegmentsAdvanced(const struct qrcodegen_Segment segs[], siz
 	}
 	
 	// Concatenate all segments to create the data bit string
-	int dataCapacityBits = getNumDataCodewords(version, ecl) * 8;
 	memset(qrcode, 0, qrcodegen_BUFFER_LEN_FOR_VERSION(version) * sizeof(qrcode[0]));
 	int bitLen = 0;
 	for (size_t i = 0; i < len; i++) {
@@ -935,16 +934,18 @@ bool qrcodegen_encodeSegmentsAdvanced(const struct qrcodegen_Segment segs[], siz
 	}
 	
 	// Add terminator and pad up to a byte if applicable
+	int dataCapacityBits = getNumDataCodewords(version, ecl) * 8;
+	assert(bitLen <= dataCapacityBits);
 	int terminatorBits = dataCapacityBits - bitLen;
 	if (terminatorBits > 4)
 		terminatorBits = 4;
 	appendBitsToBuffer(0, terminatorBits, qrcode, &bitLen);
 	appendBitsToBuffer(0, (8 - bitLen % 8) % 8, qrcode, &bitLen);
+	assert(bitLen % 8 == 0);
 	
-	// Pad with alternate bytes until data capacity is reached
+	// Pad with alternating bytes until data capacity is reached
 	for (uint8_t padByte = 0xEC; bitLen < dataCapacityBits; padByte ^= 0xEC ^ 0x11)
 		appendBitsToBuffer(padByte, 8, qrcode, &bitLen);
-	assert(bitLen % 8 == 0);
 	
 	// Draw function and data codeword modules
 	addEccAndInterleave(qrcode, version, ecl, tempBuffer);

cpp/QrCode.cpp

@@ -87,7 +87,6 @@ QrCode QrCode::encodeSegments(const vector<QrSegment> &segs, Ecc ecl,
 	}
 	
 	// Concatenate all segments to create the data bit string
-	size_t dataCapacityBits = getNumDataCodewords(version, ecl) * 8;
 	BitBuffer bb;
 	for (const QrSegment &seg : segs) {
 		bb.appendBits(seg.getMode().getModeBits(), 4);
@@ -96,15 +95,18 @@ QrCode QrCode::encodeSegments(const vector<QrSegment> &segs, Ecc ecl,
 	}
 	
 	// Add terminator and pad up to a byte if applicable
+	size_t dataCapacityBits = getNumDataCodewords(version, ecl) * 8;
+	if (bb.size() > dataCapacityBits)
+		throw std::logic_error("Assertion error");
 	bb.appendBits(0, std::min<size_t>(4, dataCapacityBits - bb.size()));
 	bb.appendBits(0, (8 - bb.size() % 8) % 8);
-	
-	// Pad with alternate bytes until data capacity is reached
-	for (uint8_t padByte = 0xEC; bb.size() < dataCapacityBits; padByte ^= 0xEC ^ 0x11)
-		bb.appendBits(padByte, 8);
 	if (bb.size() % 8 != 0)
 		throw std::logic_error("Assertion error");
 	
+	// Pad with alternating bytes until data capacity is reached
+	for (uint8_t padByte = 0xEC; bb.size() < dataCapacityBits; padByte ^= 0xEC ^ 0x11)
+		bb.appendBits(padByte, 8);
+	
 	// Create the QR Code symbol
 	return QrCode(version, ecl, bb.getBytes(), mask);
 }

java/io/nayuki/qrcodegen/QrCode.java

@@ -141,7 +141,6 @@ public final class QrCode {
 		}
 		
 		// Concatenate all segments to create the data bit string
-		int dataCapacityBits = getNumDataCodewords(version, ecl) * 8;
 		BitBuffer bb = new BitBuffer();
 		for (QrSegment seg : segs) {
 			bb.appendBits(seg.mode.modeBits, 4);
@@ -150,13 +149,15 @@ public final class QrCode {
 		}
 		
 		// Add terminator and pad up to a byte if applicable
+		int dataCapacityBits = getNumDataCodewords(version, ecl) * 8;
+		assert bb.bitLength() <= dataCapacityBits;
 		bb.appendBits(0, Math.min(4, dataCapacityBits - bb.bitLength()));
 		bb.appendBits(0, (8 - bb.bitLength() % 8) % 8);
+		assert bb.bitLength() % 8 == 0;
 		
-		// Pad with alternate bytes until data capacity is reached
+		// Pad with alternating bytes until data capacity is reached
 		for (int padByte = 0xEC; bb.bitLength() < dataCapacityBits; padByte ^= 0xEC ^ 0x11)
 			bb.appendBits(padByte, 8);
-		assert bb.bitLength() % 8 == 0;
 		
 		// Create the QR Code symbol
 		return new QrCode(version, ecl, bb.getBytes(), mask);

javascript/qrcodegen.js

@@ -554,7 +554,6 @@ var qrcodegen = new function() {
 		});
 		
 		// Concatenate all segments to create the data bit string
-		var dataCapacityBits = QrCode.getNumDataCodewords(version, ecl) * 8;
 		var bb = new BitBuffer();
 		segs.forEach(function(seg) {
 			bb.appendBits(seg.mode.modeBits, 4);
@@ -565,15 +564,18 @@ var qrcodegen = new function() {
 		});
 		
 		// Add terminator and pad up to a byte if applicable
+		var dataCapacityBits = QrCode.getNumDataCodewords(version, ecl) * 8;
+		if (bb.length > dataCapacityBits)
+			throw "Assertion error";
 		bb.appendBits(0, Math.min(4, dataCapacityBits - bb.length));
 		bb.appendBits(0, (8 - bb.length % 8) % 8);
-		
-		// Pad with alternate bytes until data capacity is reached
-		for (var padByte = 0xEC; bb.length < dataCapacityBits; padByte ^= 0xEC ^ 0x11)
-			bb.appendBits(padByte, 8);
 		if (bb.length % 8 != 0)
 			throw "Assertion error";
 		
+		// Pad with alternating bytes until data capacity is reached
+		for (var padByte = 0xEC; bb.length < dataCapacityBits; padByte ^= 0xEC ^ 0x11)
+			bb.appendBits(padByte, 8);
+		
 		// Create the QR Code symbol
 		return new this(bb.getBytes(), mask, version, ecl);
 	};

python/qrcodegen.py

@@ -116,7 +116,6 @@ class QrCode(object):
 				ecl = newecl
 		
 		# Concatenate all segments to create the data bit string
-		datacapacitybits = QrCode._get_num_data_codewords(version, ecl) * 8
 		bb = _BitBuffer()
 		for seg in segs:
 			bb.append_bits(seg.get_mode().get_mode_bits(), 4)
@@ -124,15 +123,17 @@ class QrCode(object):
 			bb.extend(seg._bitdata)
 		
 		# Add terminator and pad up to a byte if applicable
+		datacapacitybits = QrCode._get_num_data_codewords(version, ecl) * 8
+		assert len(bb) <= datacapacitybits
 		bb.append_bits(0, min(4, datacapacitybits - len(bb)))
 		bb.append_bits(0, -len(bb) % 8)  # Note: Python's modulo on negative numbers behaves better than C family languages
+		assert len(bb) % 8 == 0
 		
-		# Pad with alternate bytes until data capacity is reached
+		# Pad with alternating bytes until data capacity is reached
 		for padbyte in itertools.cycle((0xEC, 0x11)):
 			if len(bb) >= datacapacitybits:
 				break
 			bb.append_bits(padbyte, 8)
-		assert len(bb) % 8 == 0
 		
 		# Create the QR Code symbol
 		return QrCode(bb.get_bytes(), mask, version, ecl)

rust/src/lib.rs

@@ -130,7 +130,6 @@ impl QrCode {
 		}
 		
 		// Concatenate all segments to create the data bit string
-		let datacapacitybits: usize = QrCode::get_num_data_codewords(version, ecl) * 8;
 		let mut bb = BitBuffer(Vec::new());
 		for seg in segs {
 			bb.append_bits(seg.mode.mode_bits(), 4);
@@ -139,19 +138,21 @@ impl QrCode {
 		}
 		
 		// Add terminator and pad up to a byte if applicable
+		let datacapacitybits: usize = QrCode::get_num_data_codewords(version, ecl) * 8;
+		assert!(bb.0.len() <= datacapacitybits);
 		let numzerobits = std::cmp::min(4, datacapacitybits - bb.0.len());
 		bb.append_bits(0, numzerobits as u8);
 		let numzerobits = bb.0.len().wrapping_neg() & 7;
 		bb.append_bits(0, numzerobits as u8);
+		assert_eq!(bb.0.len() % 8, 0, "Assertion error");
 		
-		// Pad with alternate bytes until data capacity is reached
+		// Pad with alternating bytes until data capacity is reached
 		for padbyte in [0xEC, 0x11].iter().cycle() {
 			if bb.0.len() >= datacapacitybits {
 				break;
 			}
 			bb.append_bits(*padbyte, 8);
 		}
-		assert_eq!(bb.0.len() % 8, 0, "Assertion error");
 		
 		let mut bytes = vec![0u8; bb.0.len() / 8];
 		for (i, bit) in bb.0.iter().enumerate() {

typescript/qrcodegen.ts

@@ -101,7 +101,6 @@ namespace qrcodegen {
 			});
 			
 			// Concatenate all segments to create the data bit string
-			let dataCapacityBits: int = QrCode.getNumDataCodewords(version, ecl) * 8;
 			let bb = new BitBuffer();
 			segs.forEach((seg: QrSegment) => {
 				bb.appendBits(seg.mode.modeBits, 4);
@@ -111,15 +110,18 @@ namespace qrcodegen {
 			});
 			
 			// Add terminator and pad up to a byte if applicable
+			let dataCapacityBits: int = QrCode.getNumDataCodewords(version, ecl) * 8;
+			if (bb.length > dataCapacityBits)
+				throw "Assertion error";
 			bb.appendBits(0, Math.min(4, dataCapacityBits - bb.length));
 			bb.appendBits(0, (8 - bb.length % 8) % 8);
-			
-			// Pad with alternate bytes until data capacity is reached
-			for (let padByte = 0xEC; bb.length < dataCapacityBits; padByte ^= 0xEC ^ 0x11)
-				bb.appendBits(padByte, 8);
 			if (bb.length % 8 != 0)
 				throw "Assertion error";
 			
+			// Pad with alternating bytes until data capacity is reached
+			for (let padByte = 0xEC; bb.length < dataCapacityBits; padByte ^= 0xEC ^ 0x11)
+				bb.appendBits(padByte, 8);
+			
 			// Create the QR Code symbol
 			return new QrCode(bb.getBytes(), mask, version, ecl);
 		}