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tokenize.c
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tokenize.c
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#include "chinnacc.h"
#include <stddef.h>
#include <stdio.h>
#include <string.h>
// Start of input string
static char *current_input;
// input filename
static char *current_filename;
// Reports an error and exit prog
// Takes in a var num of error params
void error(char *fmt, ...) {
va_list ap;
va_start(ap, fmt);
vfprintf(stderr, fmt, ap);
fprintf(stderr, "\n");
exit(1);
}
// Reports an error message in the following format and exit.
// e.g.
// foo.c:10 x = y + 1;
// ^ <error message here>
static void verror_at(char *loc, char *fmt, va_list ap) {
// int pos = loc - current_input;
// fprintf(stderr, "%s\n", current_input);
// first we need to find the start of the line containing the loc
char *line = loc;
// first condition is in case we are on the first line
while (current_input < line && line[-1] != '\n')
line--; // keep going backwards till hitting start of input or newline char
char *end = loc;
while (*end != '\n')
end++; // go to newline char at end of line. TODO: what happens if error on last line
// without terminating new line char? -> we make sure there is an ending \n when tokenizing file
// determine the line number
int line_no = 1;
for (char *p = current_input; p < line; p++)
if (*p == '\n')
line_no++;
// print out line
int leading = fprintf(stderr, "%s:%d: ", current_filename, line_no); // returns number of chars written
fprintf(stderr, "%.*s\n", (int) (end - line), line); // TODO: find out how this format string works
// error message, taking into account indent needed for the leading part
int pos = loc - line + leading;
fprintf(stderr, "%*s^ ", pos, ""); // prepends sufficient spaces so that the caret sign is pointing up at the correct char
vfprintf(stderr, fmt, ap);
fprintf(stderr, "\n");
exit(1);
}
void error_at(char *loc, char *fmt, ...) {
va_list ap;
va_start(ap, fmt);
verror_at(loc, fmt, ap);
}
void error_tok(Token *tok, char *fmt, ...) {
va_list ap;
va_start(ap, fmt);
verror_at(tok->loc, fmt, ap);
}
/* HELPER FUNCTIONS */
// Compares current token string to s
bool equal(Token *tok, char *s) {
return memcmp(tok->loc, s, tok->len) == 0
&& s[tok->len] == '\0'; //check if null terminated string
}
// Asserts that current token matches the char `s`.
// If so, returns the pointer to the next token
Token *skip(Token *tok, char *s) {
if (!equal(tok, s)) {
error_tok(tok, "Expected '%s'", s);
}
return tok->next;
}
// if next set of chars match 'str' return true and consume it in token stream
bool consume(Token **tok_loc, char *str) {
Token *tok = *tok_loc;
if (equal(tok, str)) {
*tok_loc = tok->next;
return true;
}
return false;
}
static Token *new_token(TokenKind kind, char *start, char *end) {
Token *tok = calloc(1, sizeof(Token));
tok->kind = kind;
tok->loc = start;
tok->len = end - start;
return tok;
}
// check if char is valid as the leading char of identifier
static bool is_ident_lead(char c) {
// allowed chars: [a-zA-Z_]
return (('a' <= c && c <= 'z') || ('A' <= c && c <= 'Z') || c == '_');
}
// checks if char is valid as a non-leading char of identifier
static bool is_ident_non_lead(char c) {
// additionally allows 0-9 as possible chars
return is_ident_lead(c) || ('0' <= c && c <= '9');
}
// compares the leading chars with some short string q
static bool startswith(char *p, char *q) {
return strncmp(p, q, strlen(q)) == 0;
}
// assumes it is a valid hex char from 0-9[a-f|A-F]
static int from_hex_char(char c) {
if ('0' <= c && c <= '9') // is numeric
return c - '0';
if ('a' <= c && c <= 'f')
return c - 'a' + 10;
return c - 'A' + 10;
}
// returns the length of the punct to consume
// if one of the equality operators returns 2, otherwise 1 if a punct
static int read_punct(char *p) {
if (startswith(p, "==") || startswith(p, "!=") ||
startswith(p, "<=") || startswith(p, ">=")) {
return 2;
}
return ispunct(*p) ? 1 : 0;
}
static bool is_keyword(Token *tok) {
static char *keyword_list[] = {
"return", "if", "else", "for", "while", "do", "int", "sizeof", "char"
};
// using size of instead of the list size to accomodate growth in list easily
for (int i=0; i < sizeof(keyword_list) / sizeof(*keyword_list); i++) {
if (equal(tok, keyword_list[i])) {
return true;
}
}
return false;
}
// read escape char and return the char it is supposed to represent, meant to be used after reading
// in a leading backslash char
static int read_escaped_char(char **char_pos, char *p) {
// if octal escape sequence, 1-3 octal numbers
if ('0' <= *p && *p <= '7') {
int octal_num = *p++ - '0';
if ('0' <= *p && *p <= '7') {
octal_num = (octal_num << 3) + (*p++ - '0');
if ('0' <= *p && *p <= '7')
octal_num = (octal_num << 3) + (*p++ - '0');
}
*char_pos = p;
return octal_num;
}
// if its a hex sequence
if (*p == 'x') {
p++;
if (!isxdigit(*p))
error_at(p, "invalid hex escape sequence");
int hex_num = 0;
while (isxdigit(*p))
hex_num = (hex_num << 4) + (from_hex_char(*p++));
*char_pos = p;
return hex_num;
}
// we will be just skipping a single char for the remaining case(s)
*char_pos = p + 1;
// we choose to define the meaning of each escaped char using our original compiler's definition
// apparently this helps with correctness and security of generated code
// TODO: read this: https://github.com/rui314/chibicc/wiki/thompson1984.pdf
switch (*p) {
case 'a': return '\a';
case 'b': return '\b';
case 't': return '\t';
case 'n': return '\n';
case 'v': return '\v';
case 'f': return '\f';
case 'r': return '\r';
case 'e': return 27; // this is a GNU C extension for the ASCII escape char
default: return *p;
}
}
static char *find_string_literal_end(char *p) {
char *start = p - 1;
// terminate once we reach the closing double quotation char
for (; *p != '"'; p++) {
// single line string literals cannot contain these two chars
if (*p == '\n' || *p == '\0')
error_at(start, "unclosed string literal");
// we skip due to possibility of string literal containing an escaped closing quotation char
if (*p == '\\')
p++;
}
return p; // return the ponter to the end of the string literal
}
// we will have to manually read in the characters char by char instead of using strndup
// so as to properly handle escaped chars
static Token *read_string_literal(char *start) {
char *end = find_string_literal_end(start + 1);
char *buf = calloc(1, end - start); // it might be more than we need but not a big issue (1 extra for each escape char)
int len = 0; // to determine the true len of the string
for (char *p = start + 1; p < end;) {
// start of escaped character
if (*p == '\\')
buf[len++] = read_escaped_char(&p, p + 1); // we only increase len by 1
else
buf[len++] = *p++;
}
Token *tok = new_token(TK_STR, start, end + 1); // factor in closing quotes
tok->ty = arr_of(ty_char, len + 1); // we need to factor in the null char at the end
tok->str = buf;
return tok;
}
// Do one pass to convert tokens containing keywords (classified as identifiers) into keyword type tokens
static void convert_keywords(Token *tok) {
for (Token *t = tok; t; t = t->next) {
if (is_keyword(t)) {
t->kind = TK_KEYWORD;
}
}
}
// Tokenize the input string and returns the new tokens
// current input is a global pointer for error reporting purposes
static Token *tokenize(char *filename, char *p) {
current_input = p;
current_filename = filename;
Token head = {};
Token *curr = &head;
while (*p) {
// skip line comments
if (startswith(p, "//")) {
p += 2;
// ignore while no newline encountered
while (*p != '\n')
p++;
continue;
}
// skip block comments
if (startswith(p, "/*")) {
char *q = strstr(p + 2, "*/"); // finds ptr to first occurence of substr in string
if (!q)
error_at(p, "unclosed block comment");
p = q + 2;
continue;
}
// Skip whitespace chars
if (isspace(*p)) {
p++;
continue;
}
// Numeric literal
if (isdigit(*p)) {
// we dont advance the p to the end here as that is being done by strtoul
curr = curr->next = new_token(TK_NUM, p, p);
char *start = p;
curr->val = strtoul(p, &p, 10); // max we can read in is 1 ul worth of digits, also cant read in hexa or octa digits
// strtoul also advances pointer p to after the number ends
curr->len = p - start;
continue;
}
// string literal
if (*p == '"') {
curr = curr->next = read_string_literal(p);
p += curr->len;
continue;
}
// identifier or possibly keyword
if (is_ident_lead(*p)) {
char *start = p;
do {
p++; // keep reading and advancing pointer as char is valid as identifier characters
} while (is_ident_non_lead(*p));
curr = curr->next = new_token(TK_IDENT, start, p);
continue;
}
// Punctuation
int punct_len = read_punct(p);
if (punct_len) {
curr = curr->next = new_token(TK_PUNCT, p, p+punct_len);
p += punct_len;
continue;
}
error_at(p, "invalid token");
}
curr = curr->next = new_token(TK_EOF, p, p);
convert_keywords(head.next);
return head.next;
}
// Read contents of file into a char buff. Can currently read up in 4096 characters per batch
static char *read_file(char *path) {
FILE *fp;
// read from stdin if filename is "-"
if (strcmp(path, "-") == 0) {
fp = stdin;
} else {
fp = fopen(path, "r");
if (!fp)
error("cannot open %s: %s", path, strerror(errno));
}
char *buf;
size_t buflen;
FILE *out = open_memstream(&buf, &buflen); // store file in memory
for (;;) {
char tmp_buf[4096];
int n = fread(tmp_buf, 1, sizeof(tmp_buf), fp);
if (n == 0) // no more bytes left to read
break;
fwrite(tmp_buf, 1, n, out);
}
if (fp != stdin)
fclose(fp);
fflush(out); // forces any unwritten bytes from the tmp buf to be written before continuing
// if its an empty file or does not terminate with a newline
if (buflen == 0 || buf[buflen - 1] != '\n')
fputc('\n', out);
// ensure that after the newline char is trailed by null char.
// this is because the main tokenization function runs till hitting a null character
fputc('\0', out);
fclose(out);
return buf;
}
Token *tokenize_file(char *path) {
return tokenize(path, read_file(path));
}