Continued implementing C library by adding functions to append Reed-Solomon ECC and interleave blocks.

c/qrcodegen.c

@@ -39,6 +39,8 @@ static void drawWhiteFunctionModules(uint8_t qrcode[], int version);
 static void drawFormatBits(enum qrcodegen_Ecc ecl, enum qrcodegen_Mask mask, uint8_t qrcode[], int size);
 static int getAlignmentPatternPositions(int version, uint8_t result[7]);
 
+static void appendErrorCorrection(uint8_t data[], int version, enum qrcodegen_Ecc ecl, uint8_t result[]);
+static int getNumRawDataModules(int version);
 static void drawCodewords(const uint8_t data[], int dataLen, uint8_t qrcode[], int version);
 static void applyMask(const uint8_t functionModules[], uint8_t qrcode[], int size, int mask);
 
@@ -48,6 +50,28 @@ static uint8_t finiteFieldMultiply(uint8_t x, uint8_t y);
 
 
 
+/*---- Private tables of constants ----*/
+
+static const int16_t NUM_ERROR_CORRECTION_CODEWORDS[4][41] = {
+	// Version: (note that index 0 is for padding, and is set to an illegal value)
+	//0,  1,  2,  3,  4,  5,   6,   7,   8,   9,  10,  11,  12,  13,  14,  15,  16,  17,  18,  19,  20,  21,  22,  23,  24,   25,   26,   27,   28,   29,   30,   31,   32,   33,   34,   35,   36,   37,   38,   39,   40    Error correction level
+	{-1,  7, 10, 15, 20, 26,  36,  40,  48,  60,  72,  80,  96, 104, 120, 132, 144, 168, 180, 196, 224, 224, 252, 270, 300,  312,  336,  360,  390,  420,  450,  480,  510,  540,  570,  570,  600,  630,  660,  720,  750},  // Low
+	{-1, 10, 16, 26, 36, 48,  64,  72,  88, 110, 130, 150, 176, 198, 216, 240, 280, 308, 338, 364, 416, 442, 476, 504, 560,  588,  644,  700,  728,  784,  812,  868,  924,  980, 1036, 1064, 1120, 1204, 1260, 1316, 1372},  // Medium
+	{-1, 13, 22, 36, 52, 72,  96, 108, 132, 160, 192, 224, 260, 288, 320, 360, 408, 448, 504, 546, 600, 644, 690, 750, 810,  870,  952, 1020, 1050, 1140, 1200, 1290, 1350, 1440, 1530, 1590, 1680, 1770, 1860, 1950, 2040},  // Quartile
+	{-1, 17, 28, 44, 64, 88, 112, 130, 156, 192, 224, 264, 308, 352, 384, 432, 480, 532, 588, 650, 700, 750, 816, 900, 960, 1050, 1110, 1200, 1260, 1350, 1440, 1530, 1620, 1710, 1800, 1890, 1980, 2100, 2220, 2310, 2430},  // High
+};
+
+const int8_t NUM_ERROR_CORRECTION_BLOCKS[4][41] = {
+	// Version: (note that index 0 is for padding, and is set to an illegal value)
+	//0, 1, 2, 3, 4, 5, 6, 7, 8, 9,10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40    Error correction level
+	{-1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 4,  4,  4,  4,  4,  6,  6,  6,  6,  7,  8,  8,  9,  9, 10, 12, 12, 12, 13, 14, 15, 16, 17, 18, 19, 19, 20, 21, 22, 24, 25},  // Low
+	{-1, 1, 1, 1, 2, 2, 4, 4, 4, 5, 5,  5,  8,  9,  9, 10, 10, 11, 13, 14, 16, 17, 17, 18, 20, 21, 23, 25, 26, 28, 29, 31, 33, 35, 37, 38, 40, 43, 45, 47, 49},  // Medium
+	{-1, 1, 1, 2, 2, 4, 4, 6, 6, 8, 8,  8, 10, 12, 16, 12, 17, 16, 18, 21, 20, 23, 23, 25, 27, 29, 34, 34, 35, 38, 40, 43, 45, 48, 51, 53, 56, 59, 62, 65, 68},  // Quartile
+	{-1, 1, 1, 2, 4, 4, 4, 5, 6, 8, 8, 11, 11, 16, 16, 18, 16, 19, 21, 25, 25, 25, 34, 30, 32, 35, 37, 40, 42, 45, 48, 51, 54, 57, 60, 63, 66, 70, 74, 77, 81},  // High
+};
+
+
+
 /*---- Function implementations ----*/
 
 // Public function - see documentation comment in header file.
@@ -312,6 +336,66 @@ static int getAlignmentPatternPositions(int version, uint8_t result[7]) {
 }
 
 
+// Appends error correction bytes to each block of the given data array, then interleaves bytes
+// from the blocks and stores them in the result array. data[0 : rawCodewords - totalEcc] contains
+// the input data. data[rawCodewords - totalEcc : rawCodewords] is used as a temporary work area
+// and will be clobbered by this function. The final answer is stored in result[0 : rawCodewords].
+static void appendErrorCorrection(uint8_t data[], int version, enum qrcodegen_Ecc ecl, uint8_t result[]) {
+	// Calculate parameter numbers
+	assert(0 <= (int)ecl && (int)ecl < 4 && 1 <= version && version <= 40);
+	int numBlocks = NUM_ERROR_CORRECTION_BLOCKS[(int)ecl][version];
+	int totalEcc = NUM_ERROR_CORRECTION_CODEWORDS[(int)ecl][version];
+	assert(totalEcc % numBlocks == 0);
+	int blockEccLen = totalEcc / numBlocks;
+	int rawCodewords = getNumRawDataModules(version) / 8;
+	int dataLen = rawCodewords - totalEcc;
+	int numShortBlocks = numBlocks - rawCodewords % numBlocks;
+	int shortBlockDataLen = rawCodewords / numBlocks - blockEccLen;
+	
+	// Split data into blocks and append ECC after all data
+	uint8_t generator[30];
+	calcReedSolomonGenerator(blockEccLen, generator);
+	for (int i = 0, j = dataLen, k = 0; i < numBlocks; i++) {
+		int blockLen = shortBlockDataLen;
+		if (i >= numShortBlocks)
+			blockLen++;
+		calcReedSolomonRemainder(&data[k], blockLen, generator, blockEccLen, &data[j]);
+		j += blockEccLen;
+		k += blockLen;
+	}
+	
+	// Interleave (not concatenate) the bytes from every block into a single sequence
+	for (int i = 0, k = 0; i < numBlocks; i++) {
+		for (int j = 0, l = i; j < shortBlockDataLen; j++, k++, l += numBlocks)
+			result[l] = data[k];
+		if (i >= numShortBlocks)
+			k++;
+	}
+	for (int i = numShortBlocks, l = numBlocks * shortBlockDataLen, k = (numShortBlocks + 1) * shortBlockDataLen;
+			i < numBlocks; i++, k += shortBlockDataLen + 1, l++)
+		result[l] = data[k];
+	for (int i = 0, k = dataLen; i < numBlocks; i++) {
+		for (int j = 0, l = dataLen + i; j < blockEccLen; j++, k++, l += numBlocks)
+			result[l] = data[k];
+	}
+}
+
+
+// Returns the number of data bits that can be stored in a QR Code of the given version number, after
+// all function modules are excluded. This includes remainder bits, so it may not be a multiple of 8.
+static int getNumRawDataModules(int version) {
+	assert(1 <= version && version <= 40);
+	int result = (16 * version + 128) * version + 64;
+	if (version >= 2) {
+		int numAlign = version / 7 + 2;
+		result -= (25 * numAlign - 10) * numAlign - 55;
+		if (version >= 7)
+			result -= 18 * 2;  // Subtract version information
+	}
+	return result;
+}
+
+
 // Draws the raw codewords (including data and ECC) onto the given QR Code. This requires the initial state of
 // the QR Code to be black at function modules and white at codeword modules (including unused remainder bits).
 static void drawCodewords(const uint8_t data[], int dataLen, uint8_t qrcode[], int version) {