Avoid undefined behaviour by avoiding pointing one before the first element of an...

[r18662]

diff --git a/lexer.c b/lexer.c
index be337ac..e8c183c 100644 (file)
--- a/lexer.c
+++ b/lexer.c
@@ -62,8 +62,8 @@ static void parse_error(const char *msg)
 
 static inline void next_real_char(void)
 {
-       bufpos++;
-       if(bufpos >= bufend) {
+       assert(bufpos <= bufend);
+       if (bufpos >= bufend) {
                size_t s = fread(buf + MAX_PUTBACK, 1, sizeof(buf) - MAX_PUTBACK,
                                 input);
                if(s == 0) {
@@ -73,20 +73,13 @@ static inline void next_real_char(void)
                bufpos = buf + MAX_PUTBACK;
                bufend = buf + MAX_PUTBACK + s;
        }
-       c = *(bufpos);
+       c = *bufpos++;
 }
 
 static inline void put_back(int pc)
 {
-       assert(bufpos >= buf);
-       //assert(bufpos < buf+MAX_PUTBACK || *bufpos == pc);
-
-       char *p = buf + (bufpos - buf);
-       *p = (char) pc;
-
-       /* going backwards in the buffer is legal as long as it's not more often
-        * than MAX_PUTBACK */
-       bufpos--;
+       assert(bufpos > buf);
+       *(--bufpos - buf + buf) = pc;
 
 #ifdef DEBUG_CHARS
        printf("putback '%c'\n", pc);
@@ -1303,6 +1296,8 @@ void lexer_open_stream(FILE *stream, const char *input_name)
        lexer_token.source_position.input_name = input_name;
 
        symbol_L = symbol_table_insert("L");
+       bufpos = NULL;
+       bufend = NULL;
 
        /* place a virtual \n at the beginning so the lexer knows that we're
         * at the beginning of a line */