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QR-Code-generator
mirror of https://github.com/nayuki/QR-Code-generator
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Clarified a magic value in C code and reflowed some associated comments.

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pull/174/head
Project Nayuki 3 years ago
parent 0dbd3b2133
commit c147f7e328
1 changed files with 23 additions and 17 deletions
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40
c/qrcodegen.c
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@ -93,6 +93,9 @@ static int numCharCountBits(enum qrcodegen_Mode mode, int version);
// value maps to the index in the string. For checking text and encoding segments.
static const char *ALPHANUMERIC_CHARSET = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ $%*+-./:";
// Sentinel value for use in only some functions.
#define LENGTH_OVERFLOW -1
// For generating error correction codes.
testable const int8_t ECC_CODEWORDS_PER_BLOCK[4][41] = {
// Version: (note that index 0 is for padding, and is set to an illegal value)
@ -150,7 +153,7 @@ bool qrcodegen_encodeText(const char *text, uint8_t tempBuffer[], uint8_t qrcode
tempBuffer[i] = (uint8_t)text[i];
seg.mode = qrcodegen_Mode_BYTE;
seg.bitLength = calcSegmentBitLength(seg.mode, textLen);
if (seg.bitLength == -1)
if (seg.bitLength == LENGTH_OVERFLOW)
goto fail;
seg.numChars = (int)textLen;
seg.data = tempBuffer;
@ -170,7 +173,7 @@ bool qrcodegen_encodeBinary(uint8_t dataAndTemp[], size_t dataLen, uint8_t qrcod
struct qrcodegen_Segment seg;
seg.mode = qrcodegen_Mode_BYTE;
seg.bitLength = calcSegmentBitLength(seg.mode, dataLen);
if (seg.bitLength == -1) {
if (seg.bitLength == LENGTH_OVERFLOW) {
qrcode[0] = 0; // Set size to invalid value for safety
return false;
}
@ -212,14 +215,14 @@ bool qrcodegen_encodeSegmentsAdvanced(const struct qrcodegen_Segment segs[], siz
for (version = minVersion; ; version++) {
int dataCapacityBits = getNumDataCodewords(version, ecl) * 8; // Number of data bits available
dataUsedBits = getTotalBits(segs, len, version);
if (dataUsedBits != -1 && dataUsedBits <= dataCapacityBits)
if (dataUsedBits != LENGTH_OVERFLOW && dataUsedBits <= dataCapacityBits)
break; // This version number is found to be suitable
if (version >= maxVersion) { // All versions in the range could not fit the given data
qrcode[0] = 0; // Set size to invalid value for safety
return false;
}
}
assert(dataUsedBits != -1);
assert(dataUsedBits != LENGTH_OVERFLOW);
// Increase the error correction level while the data still fits in the current version number
for (int i = (int)qrcodegen_Ecc_MEDIUM; i <= (int)qrcodegen_Ecc_HIGH; i++) { // From low to high
@ -831,7 +834,7 @@ bool qrcodegen_isAlphanumeric(const char *text) {
// Public function - see documentation comment in header file.
size_t qrcodegen_calcSegmentBufferSize(enum qrcodegen_Mode mode, size_t numChars) {
int temp = calcSegmentBitLength(mode, numChars);
if (temp == -1)
if (temp == LENGTH_OVERFLOW)
return SIZE_MAX;
assert(0 <= temp && temp <= INT16_MAX);
return ((size_t)temp + 7) / 8;
@ -840,8 +843,8 @@ size_t qrcodegen_calcSegmentBufferSize(enum qrcodegen_Mode mode, size_t numChars
// 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).
// - Returns LENGTH_OVERFLOW 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 mode, numChars must be 0, and the worst-case number of bits is returned.
@ -849,7 +852,7 @@ size_t qrcodegen_calcSegmentBufferSize(enum qrcodegen_Mode mode, size_t numChars
testable int calcSegmentBitLength(enum qrcodegen_Mode mode, size_t numChars) {
// All calculations are designed to avoid overflow on all platforms
if (numChars > (unsigned int)INT16_MAX)
return -1;
return LENGTH_OVERFLOW;
long result = (long)numChars;
if (mode == qrcodegen_Mode_NUMERIC)
result = (result * 10 + 2) / 3; // ceil(10/3 * n)
@ -863,11 +866,11 @@ testable int calcSegmentBitLength(enum qrcodegen_Mode mode, size_t numChars) {
result = 3 * 8;
else { // Invalid argument
assert(false);
return -1;
return LENGTH_OVERFLOW;
}
assert(result >= 0);
if (result > INT16_MAX)
return -1;
return LENGTH_OVERFLOW;
return (int)result;
}
@ -878,7 +881,7 @@ struct qrcodegen_Segment qrcodegen_makeBytes(const uint8_t data[], size_t len, u
struct qrcodegen_Segment result;
result.mode = qrcodegen_Mode_BYTE;
result.bitLength = calcSegmentBitLength(result.mode, len);
assert(result.bitLength != -1);
assert(result.bitLength != LENGTH_OVERFLOW);
result.numChars = (int)len;
if (len > 0)
memcpy(buf, data, len * sizeof(buf[0]));
@ -894,7 +897,7 @@ struct qrcodegen_Segment qrcodegen_makeNumeric(const char *digits, uint8_t buf[]
size_t len = strlen(digits);
result.mode = qrcodegen_Mode_NUMERIC;
int bitLen = calcSegmentBitLength(result.mode, len);
assert(bitLen != -1);
assert(bitLen != LENGTH_OVERFLOW);
result.numChars = (int)len;
if (bitLen > 0)
memset(buf, 0, ((size_t)bitLen + 7) / 8 * sizeof(buf[0]));
@ -928,7 +931,7 @@ struct qrcodegen_Segment qrcodegen_makeAlphanumeric(const char *text, uint8_t bu
size_t len = strlen(text);
result.mode = qrcodegen_Mode_ALPHANUMERIC;
int bitLen = calcSegmentBitLength(result.mode, len);
assert(bitLen != -1);
assert(bitLen != LENGTH_OVERFLOW);
result.numChars = (int)len;
if (bitLen > 0)
memset(buf, 0, ((size_t)bitLen + 7) / 8 * sizeof(buf[0]));
@ -983,8 +986,8 @@ struct qrcodegen_Segment qrcodegen_makeEci(long assignVal, uint8_t buf[]) {
// Calculates the number of bits needed to encode the given segments at the given version.
// Returns a non-negative number if successful. Otherwise returns -1 if a segment has too
// many characters to fit its length field, or the total bits exceeds INT16_MAX.
// Returns a non-negative number if successful. Otherwise returns LENGTH_OVERFLOW if a segment
// has too many characters to fit its length field, or the total bits exceeds INT16_MAX.
testable int getTotalBits(const struct qrcodegen_Segment segs[], size_t len, int version) {
assert(segs != NULL || len == 0);
long result = 0;
@ -996,10 +999,10 @@ testable int getTotalBits(const struct qrcodegen_Segment segs[], size_t len, int
int ccbits = numCharCountBits(segs[i].mode, version);
assert(0 <= ccbits && ccbits <= 16);
if (numChars >= (1L << ccbits))
return -1; // The segment's length doesn't fit the field's bit width
return LENGTH_OVERFLOW; // The segment's length doesn't fit the field's bit width
result += 4L + ccbits + bitLength;
if (result > INT16_MAX)
return -1; // The sum might overflow an int type
return LENGTH_OVERFLOW; // The sum might overflow an int type
}
assert(0 <= result && result <= INT16_MAX);
return (int)result;
@ -1020,3 +1023,6 @@ static int numCharCountBits(enum qrcodegen_Mode mode, int version) {
default: assert(false); return -1; // Dummy value
}
}
#undef LENGTH_OVERFLOW

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