Separate isLetter into isUpper and isLower

include/util.hpp

@@ -26,6 +26,8 @@ bool isNewline(int c);
 bool isBlankSpace(int c);
 bool isWhitespace(int c);
 bool isPrintable(int c);
+bool isUpper(int c);
+bool isLower(int c);
 bool isLetter(int c);
 bool isDigit(int c);
 bool isBinDigit(int c);

src/fix/mbc.cpp

@@ -12,7 +12,7 @@
 
 #include "helpers.hpp"  // unreachable_
 #include "platform.hpp" // strcasecmp
-#include "util.hpp"     // isBlankSpace, isDigit
+#include "util.hpp"     // isBlankSpace, isLower, isDigit
 
 #include "fix/warning.hpp"
 
@@ -107,10 +107,10 @@ static void skipMBCSpace(char const *&ptr) {
 }
 
 static char normalizeMBCChar(char c) {
-	if (c >= 'a' && c <= 'z') { // Uppercase for comparison with `mbc_Name`s
+	if (isLower(c)) {
-		c = c - 'a' + 'A';
+		c = c - 'a' + 'A'; // Uppercase for comparison with `mbc_Name`s
-	} else if (c == '_') { // Treat underscores as spaces
+	} else if (c == '_') {
-		c = ' ';
+		c = ' '; // Treat underscores as spaces
 	}
 	return c;
 }

src/util.cpp

@@ -26,8 +26,16 @@ bool isPrintable(int c) {
 	return c >= ' ' && c <= '~';
 }
 
+bool isUpper(int c) {
+	return c >= 'A' && c <= 'Z';
+}
+
+bool isLower(int c) {
+	return c >= 'a' && c <= 'z';
+}
+
 bool isLetter(int c) {
-	return (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z');
+	return isUpper(c) || isLower(c);
 }
 
 bool isDigit(int c) {