Allow char literal convertion into unsigned (#82)

required to compile stm32mp1xxx dtb

Also includes tests.

Fixes #81

Tests/char_literals.dts

@@ -0,0 +1,13 @@
+/dts-v1/;
+
+/ {
+
+    gpio_port = <('F' - 'A')>;
+    test_nl   = <('\n')>;
+    test_cr   = <('\r')>;
+    test_tab  = <('\t')>;
+    test_bs   = <('\\')>;
+    test_sq   = <('\'')>;
+    test_zero = <('\0')>;
+
+}

Tests/char_literals.dts.expected

@@ -0,0 +1,12 @@
+/dts-v1/;
+
+/  {
+
+	gpio_port = <0x5>;
+	test_nl = <0xa>;
+	test_cr = <0xd>;
+	test_tab = <0x9>;
+	test_bs = <0x5c>;
+	test_sq = <0x27>;
+	test_zero = <0x0>;
+};

input_buffer.cc

@@ -337,6 +337,47 @@ input_buffer::consume(const char *str)
 	return false;
 }
 
+bool
+input_buffer::consume_char_literal(unsigned long long &outInt)
+{
+	outInt = (unsigned char)((*this)[0]);
+	cursor++;
+
+	if(outInt != '\\')
+	{
+		return true;
+	}
+	else if(cursor >= size)
+	{
+		return false;
+	}
+
+	outInt = (unsigned char)((*this)[0]);
+	cursor++;
+
+	switch (outInt) {
+		default:
+			return false;
+		case 'n':
+			outInt = (unsigned char)'\n';
+			break;
+		case 'r':
+			outInt = (unsigned char)'\r';
+			break;
+		case 't':
+			outInt = (unsigned char)'\t';
+			break;
+		case '0':
+			outInt = 0;
+			break;
+		case '\'':
+		case '\\':
+			break;
+	}
+
+	return true;
+}
+
 bool
 input_buffer::consume_integer(unsigned long long &outInt)
 {
@@ -874,6 +915,18 @@ expression_ptr text_input_buffer::parse_expression(bool stopAtParen)
 	source_location l = location();
 	switch (*(*this))
 	{
+		case '\'':
+			consume('\'');
+			if(!consume_char_literal(leftVal))
+			{
+				return nullptr;
+			}
+			if (!consume('\''))
+			{
+				return nullptr;
+			}
+			lhs.reset(new terminal_expr(l, leftVal));
+			break;
 		case '0'...'9':
 			if (!consume_integer(leftVal))
 			{

input_buffer.hh

@@ -193,6 +193,13 @@ class input_buffer
 	 * current point in the input.
 	 */
 	bool consume(const char *str);
+	/**
+	 * Reads unsigned from char literal.  Returns true and advances
+	 * the cursor to next char.
+	 *
+	 * The parsed value is returned via the argument.
+	 */
+	bool consume_char_literal(unsigned long long &outInt);
 	/**
 	 * Reads an integer in base 8, 10, or 16.  Returns true and advances
 	 * the cursor to the end of the integer if the cursor points to an
@@ -412,6 +419,21 @@ class text_input_buffer
 		}
 		return input_stack.top()->consume(str);
 	}
+	/**
+	 * Converts next char into unsigned
+	 *
+	 * The parsed value is returned via the argument.
+	 *
+	 * This method does not scan between files.
+	 */
+	bool consume_char_literal(unsigned long long &outInt)
+	{
+		if (input_stack.empty())
+		{
+			return false;
+		}
+		return input_stack.top()->consume_char_literal(outInt);
+	}
 	/**
 	 * Reads an integer in base 8, 10, or 16.  Returns true and advances
 	 * the cursor to the end of the integer if the cursor points to an