Lex $ff00+c without needing large peek lookahead

This also allows arbitrary amounts of whitespace in `$ff00 + c`,
instead of needing to fit in the 42-byte LEXER_BUF_SIZE

src/asm/lexer.c

@@ -350,6 +350,7 @@ struct LexerState {
 	uint32_t lineNo;
 	uint32_t colNo;
 	int lastToken;
+	int nextToken;
 
 	struct IfStack *ifStack;
 
@@ -374,6 +375,7 @@ static void initState(struct LexerState *state)
 	state->mode = LEXER_NORMAL;
 	state->atLineStart = true; /* yylex() will init colNo due to this */
 	state->lastToken = T_EOF;
+	state->nextToken = 0;
 
 	state->ifStack = NULL;
 
@@ -1778,6 +1780,14 @@ static int yylex_NORMAL(void)
 {
 	dbgPrint("Lexing in normal mode, line=%" PRIu32 ", col=%" PRIu32 "\n",
 		 lexer_GetLineNo(), lexer_GetColNo());
+
+	if (lexerState->nextToken) {
+		int token = lexerState->nextToken;
+
+		lexerState->nextToken = 0;
+		return token;
+	}
+
 	for (;;) {
 		int c = nextChar();
 		char secondChar;
@@ -1902,17 +1912,15 @@ static int yylex_NORMAL(void)
 				while (isWhitespace(c = peek(0)))
 					shiftChars(1);
 				if (c == '+') {
-					/* FIXME: not great due to large lookahead */
-					uint8_t distance = 1;
-
-					do {
-						c = peek(distance++);
-					} while (isWhitespace(c));
-
+					shiftChars(1);
+					while (isWhitespace(c = peek(0)))
+						shiftChars(1);
 					if (c == 'c' || c == 'C') {
-						shiftChars(distance);
+						shiftChars(1);
 						return T_MODE_HW_C;
 					}
+					/* Retroactively lex the plus after the $ff00 */
+					lexerState->nextToken = T_OP_ADD;
 				}
 			}
 			return T_NUMBER;

test/asm/ff00-plus-c.asm

@@ -0,0 +1,5 @@
+SECTION "test", ROM0[0]
+	ld [ $ff00 + c ], a
+	; 257 spaces exceeds both LEXER_BUF_SIZE (42) and uint8_t limit (255)
+	ld [ $ff00 +                                                                                                                                                                                                                                                                 c ], a
+	ld [ $ff00                                                                                                                                                                                                                                                                 + c ], a

test/asm/ff00-plus-c.out.bin

@@ -0,0 +1 @@
+<EFBFBD><EFBFBD><EFBFBD>