S-Record lexer: extract reusable parts of helper functions

CalcChecksum() takes a parameter to decide between one's or two's
complement. The variable "cs" has been changed to "signed int" to
simplifiy calculation of the two's complement with signed arithmetic
instead of using bitwise operations, which would cause "overflow"
warnings in Coverity without additional "& 0xFF" masking.

1 files changed, 60 insertions, 35 deletions

diff --git a/lexers/LexHex.cxx b/lexers/LexHex.cxx
index 21ce8790e..231142a1c 100644
--- a/lexers/LexHex.cxx
+++ b/lexers/LexHex.cxx
@@ -57,6 +57,8 @@ static inline bool IsNewline(const int ch);
 static int GetHexaChar(char hd1, char hd2);
 static int GetHexaChar(unsigned int pos, Accessor &styler);
 static bool ForwardWithinLine(StyleContext &sc, int nb = 1);
+static int CountByteCount(unsigned int startPos, int uncountedDigits, Accessor &styler);
+static int CalcChecksum(unsigned int startPos, int cnt, bool twosCompl, Accessor &styler);
 
 // prototypes for file format specific helper functions
 static unsigned int GetSrecRecStartPosition(unsigned int pos, Accessor &styler);
@@ -129,6 +131,62 @@ static bool ForwardWithinLine(StyleContext &sc, int nb)
 	return true;
 }
 
+// Count the number of digit pairs from <startPos> till end of record, ignoring
+// <uncountedDigits> digits.
+// If the record is too short, a negative count may be returned.
+static int CountByteCount(unsigned int startPos, int uncountedDigits, Accessor &styler)
+{
+	int cnt;
+	unsigned int pos;
+
+	pos = startPos;
+
+	while (!IsNewline(styler.SafeGetCharAt(pos, '\n'))) {
+		pos++;
+	}
+
+	// number of digits in this line minus number of digits of uncounted fields
+	cnt = static_cast<int>(pos - startPos) - uncountedDigits;
+
+	// Prepare round up if odd (digit pair incomplete), this way the byte
+	// count is considered to be valid if the checksum is incomplete.
+	if (cnt >= 0) {
+		cnt++;
+	}
+
+	// digit pairs
+	cnt /= 2;
+
+	return cnt;
+}
+
+// Calculate the checksum of the record.
+// <startPos> is the position of the first character of the starting digit
+// pair, <cnt> is the number of digit pairs.
+static int CalcChecksum(unsigned int startPos, int cnt, bool twosCompl, Accessor &styler)
+{
+	int cs = 0;
+
+	for (unsigned int pos = startPos; pos < startPos + cnt; pos += 2) {
+		int val = GetHexaChar(pos, styler);
+
+		if (val < 0) {
+			return val;
+		}
+
+		// overflow does not matter
+		cs += val;
+	}
+
+	if (twosCompl) {
+		// low byte of two's complement
+		return -cs & 0xFF;
+	} else {
+		// low byte of one's complement
+		return ~cs & 0xFF;
+	}
+}
+
 // Get the position of the record "start" field (first character in line) in
 // the record around position <pos>.
 static unsigned int GetSrecRecStartPosition(unsigned int pos, Accessor &styler)
@@ -159,28 +217,7 @@ static int GetSrecByteCount(unsigned int recStartPos, Accessor &styler)
 // If the record is too short, a negative count may be returned.
 static int CountSrecByteCount(unsigned int recStartPos, Accessor &styler)
 {
-	int cnt;
-	unsigned int pos;
-
-	pos = recStartPos;
-
-	while (!IsNewline(styler.SafeGetCharAt(pos, '\n'))) {
-		pos++;
-	}
-
-	// number of digits in this line minus number of digits of uncounted fields
-	cnt = static_cast<int>(pos - recStartPos) - 4;
-
-	// Prepare round up if odd (digit pair incomplete), this way the byte
-	// count is considered to be valid if the checksum is incomplete.
-	if (cnt >= 0) {
-		cnt++;
-	}
-
-	// digit pairs
-	cnt /= 2;
-
-	return cnt;
+	return CountByteCount(recStartPos, 4, styler);
 }
 
 // Get the size of the "address" field.
@@ -247,23 +284,11 @@ static int GetSrecChecksum(unsigned int recStartPos, Accessor &styler)
 static int CalcSrecChecksum(unsigned int recStartPos, Accessor &styler)
 {
 	int byteCount;
-	unsigned int cs = 0;
 
 	byteCount = GetSrecByteCount(recStartPos, styler);
 
 	// sum over "byte count", "address" and "data" fields (6..510 digits)
-	for (unsigned int pos = recStartPos + 2; pos < recStartPos + 2 + byteCount * 2; pos += 2) {
-		int val = GetHexaChar(pos, styler);
-
-		if (val < 0) {
-			return val;
-		}
-
-		cs += val;
-	}
-
-	// low byte of one's complement
-	return (~cs) & 0xFF;
+	return CalcChecksum(recStartPos + 2, byteCount * 2, false, styler);
 }
 
 static void ColouriseSrecDoc(unsigned int startPos, int length, int initStyle, WordList *[], Accessor &styler)