Fix conversion of BIT fields (fixes #2254)

1 files changed, 13 insertions, 14 deletions

diff --git a/Frameworks/SPMySQLFramework/Source/SPMySQLResult Categories/Data Conversion.m b/Frameworks/SPMySQLFramework/Source/SPMySQLResult Categories/Data Conversion.m
index 639ff0b9..8c5b9181 100644
--- a/Frameworks/SPMySQLFramework/Source/SPMySQLResult Categories/Data Conversion.m
+++ b/Frameworks/SPMySQLFramework/Source/SPMySQLResult Categories/Data Conversion.m
@@ -209,27 +209,26 @@ static inline NSString * _bitStringWithBytes(const char *bytes, NSUInteger lengt
 		return nil;
 	}
 
-	// Ensure padLength is never lower than the length
-	if (padLength < bitLength) {
-		padLength = bitLength;
-	}
-
+	// use whatever is smaller. padLength comes from BIT(x), bitLength from the actual bytes transmitted.
+	// if bitLength < padLength it means the value is smaller than what the field can accomodate.
+	// if bitLength > padLength it means BIT(x) is not a full n bytes long and was extended by mysqls storage.
+	//   In that case the additional bits should still be 0 as mysql does not allow to set bits over the size of x.
+	bitLength = MIN(bitLength,padLength);
 	// Generate a nul-terminated C string representation of the binary data
 	char *cStringBuffer = malloc(padLength + 1);
-	cStringBuffer[padLength] = '\0';
+	memset(cStringBuffer, '0', padLength);
 
 	while (i < bitLength)
 	{
+		// start with the least significant bit (the rightmost bit in the last byte) and move left
+		unsigned char bitInByteMask =  i % 8; // 0-7, the cycle is 0,1,...,7,0,...
+		unsigned long bytesOffset = (length - 1) - (i >> 3); // i>>3 == floor(i/8)
 		++i;
-
-		cStringBuffer[padLength - i] = ((bytes[length - 1 - (i >> 3)] >> (i & 0x7)) & 1 ) ? '1' : '0';
+		cStringBuffer[padLength - i] = ((bytes[bytesOffset] & (1 << bitInByteMask)) != 0) ? '1' : '0';
 	}
-
-	while (i++ < padLength)
-	{
-		cStringBuffer[padLength - i] = '0';
-	}
-
+	
+	cStringBuffer[padLength] = '\0';
+	
 	// Convert to a string
 	NSString *returnString = [NSString stringWithUTF8String:cStringBuffer];