Function calcSegmentBitLength

modules/data/qrcode/qrcodegen.c:732–771

Returns the number of data bits needed to represent a segment containing the given number of characters using the given mode. Notes: - Returns -1 on failure, i.e. numChars > INT16_MAX or the number of needed bits exceeds INT16_MAX (i.e. 32767). - Otherwise, all valid results are in the range [0, INT16_MAX]. - For byte mode, numChars measures the number of bytes, not Unicode code points. - For ECI

// - For ECI mode, numChars must be 0, and the worst-case number of bits is returned.
//   An actual ECI segment can have shorter data. For non-ECI modes, the result is exact.
testable int calcSegmentBitLength(enum qrcodegen_Mode mode, size_t numChars) {
	const int LIMIT = INT16_MAX;  // Can be configured as high as INT_MAX
	if (numChars > (unsigned int)LIMIT)
		return -1;
	int n = (int)numChars;
	
	int result = -2;
	if (mode == qrcodegen_Mode_NUMERIC) {
		// n * 3 + ceil(n / 3)
		if (n > LIMIT / 3)
			goto overflow;
		result = n * 3;
		int temp = n / 3 + (n % 3 == 0 ? 0 : 1);
		if (temp > LIMIT - result)
			goto overflow;
		result += temp;
	} else if (mode == qrcodegen_Mode_ALPHANUMERIC) {
		// n * 5 + ceil(n / 2)
		if (n > LIMIT / 5)
			goto overflow;
		result = n * 5;
		int temp = n / 2 + n % 2;
		if (temp > LIMIT - result)
			goto overflow;
		result += temp;
	} else if (mode == qrcodegen_Mode_BYTE) {
		if (n > LIMIT / 8)
			goto overflow;
		result = n * 8;
	} else if (mode == qrcodegen_Mode_KANJI) {
		if (n > LIMIT / 13)
			goto overflow;
		result = n * 13;
	} else if (mode == qrcodegen_Mode_ECI && numChars == 0)
		result = 3 * 8;
	assert(0 <= result && result <= LIMIT);
	return result;
overflow:
	return -1;
}


// Public function - see documentation comment in header file.