Support negative numbers in q_strnaturalcmp

Note: we only support negative numbers at the beginning of strings so that
"-2" is sorted before "-1", but "file-2345.ext" *after* "file-1234.ext".

Quake/common.c

@@ -225,9 +225,20 @@ void MultiString_Append (char **pvec, const char *str)
 
 int q_strnaturalcmp (const char *s1, const char *s2)
 {
+	qboolean neg1, neg2, sign1, sign2;
+
 	if (s1 == s2)
 		return 0;
 
+	neg1 = *s1 == '-';
+	neg2 = *s2 == '-';
+	sign1 = neg1 || *s1 == '+';
+	sign2 = neg2 || *s2 == '+';
+
+	// early out if strings start with different signs followed by digits
+	if (neg1 != neg2 && q_isdigit (s1[sign1]) && q_isdigit (s1[sign2]))
+		return neg2 - neg1;
+
 skip_prefix:
 	while (*s1 && !q_isdigit (*s1) && q_toupper (*s1) == q_toupper (*s2))
 	{
@@ -240,7 +251,7 @@ int q_strnaturalcmp (const char *s1, const char *s2)
 	{
 		const char *begin1 = s1++;
 		const char *begin2 = s2++;
-		int diff;
+		int diff, sign;
 
 		while (*begin1 == '0')
 			begin1++;
@@ -252,17 +263,23 @@ int q_strnaturalcmp (const char *s1, const char *s2)
 		while (q_isdigit (*s2))
 			s2++;
 
+		sign = neg1 ? -1 : 1;
+
 		diff = (s1 - begin1) - (s2 - begin2);
 		if (diff)
-			return diff;
+			return diff * sign;
 
 		while (begin1 != s1)
 		{
 			diff = *begin1++ - *begin2++;
 			if (diff)
-				return diff;
+				return diff * sign;
 		}
 
+		// We only support negative numbers at the beginning of strings so that
+		// "-2" is sorted before "-1", but "file-2345.ext" *after* "file-1234.ext".
+		neg1 = neg2 = false;
+
 		goto skip_prefix;
 	}