Factor out isBinDigit and parseHexDigit utility functions

src/util.cpp

@@ -5,6 +5,8 @@
 #include <stdint.h>
 #include <stdio.h>
 
+#include "helpers.hpp" // assume
+
 bool isNewline(int c) {
 	return c == '\r' || c == '\n';
 }
@@ -51,6 +53,17 @@ bool continuesIdentifier(int c) {
 	return startsIdentifier(c) || isDigit(c) || c == '#' || c == '$' || c == '@';
 }
 
+uint8_t parseHexDigit(int c) {
+	if (c >= 'A' && c <= 'F') {
+		return c - 'A' + 10;
+	} else if (c >= 'a' && c <= 'f') {
+		return c - 'a' + 10;
+	} else {
+		assume(isDigit(c));
+		return c - '0';
+	}
+}
+
 char const *printChar(int c) {
 	// "'A'" + '\0': 4 bytes
 	// "'\\n'" + '\0': 5 bytes