设计类Python编译器时如何处理tab和space缩进？

/* Get next token, after space stripping etc. */

static int
tok_get(register struct tok_state *tok, char **p_start, char **p_end)
{
    register int c;
    int blankline;

    *p_start = *p_end = NULL;
  nextline:
    tok->start = NULL;
    blankline = 0;

    /* Get indentation level */
    if (tok->atbol) {
        register int col = 0;
        register int altcol = 0;
        tok->atbol = 0;
        for (;;) {
            c = tok_nextc(tok);
            if (c == ' ')
                col++, altcol++;
            else if (c == '\t') {
                col = (col/tok->tabsize + 1) * tok->tabsize;
                altcol = (altcol/tok->alttabsize + 1)
                    * tok->alttabsize;
            }
            else if (c == '\014') /* Control-L (formfeed) */
                col = altcol = 0; /* For Emacs users */
            else
                break;
        }
        tok_backup(tok, c);
        if (c == '#' || c == '\n') {
            /* Lines with only whitespace and/or comments
               shouldn't affect the indentation and are
               not passed to the parser as NEWLINE tokens,
               except *totally* empty lines in interactive
               mode, which signal the end of a command group. */
            if (col == 0 && c == '\n' && tok->prompt != NULL)
                blankline = 0; /* Let it through */
            else
                blankline = 1; /* Ignore completely */
            /* We can't jump back right here since we still
               may need to skip to the end of a comment */
        }
        if (!blankline && tok->level == 0) {
            if (col == tok->indstack[tok->indent]) {
                /* No change */
                if (altcol != tok->altindstack[tok->indent]) {
                    if (indenterror(tok))
                        return ERRORTOKEN;
                }
            }
            else if (col > tok->indstack[tok->indent]) {
                /* Indent -- always one */
                if (tok->indent+1 >= MAXINDENT) {
                    tok->done = E_TOODEEP;
                    tok->cur = tok->inp;
                    return ERRORTOKEN;
                }
                if (altcol <= tok->altindstack[tok->indent]) {
                    if (indenterror(tok))
                        return ERRORTOKEN;
                }
                tok->pendin++;
                tok->indstack[++tok->indent] = col;
                tok->altindstack[tok->indent] = altcol;
            }
            else /* col < tok->indstack[tok->indent] */ {
                /* Dedent -- any number, must be consistent */
                while (tok->indent > 0 &&
                    col < tok->indstack[tok->indent]) {
                    tok->pendin--;
                    tok->indent--;
                }
                if (col != tok->indstack[tok->indent]) {
                    tok->done = E_DEDENT;
                    tok->cur = tok->inp;
                    return ERRORTOKEN;
                }
                if (altcol != tok->altindstack[tok->indent]) {
                    if (indenterror(tok))
                        return ERRORTOKEN;
                }
            }
        }
    }

    tok->start = tok->cur;

    /* Return pending indents/dedents */
    if (tok->pendin != 0) {
        if (tok->pendin < 0) {
            tok->pendin++;
            return DEDENT;
        }
        else {
            tok->pendin--;
            return INDENT;
        }
    }

 again:
    tok->start = NULL;
    /* Skip spaces */
    do {
        c = tok_nextc(tok);
    } while (c == ' ' || c == '\t' || c == '\014');

    /* Set start of current token */
    tok->start = tok->cur - 1;

    /* Skip comment, while looking for tab-setting magic */
    if (c == '#') {
        static char *tabforms[] = {
            "tab-width:",                       /* Emacs */
            ":tabstop=",                        /* vim, full form */
            ":ts=",                             /* vim, abbreviated form */
            "set tabsize=",                     /* will vi never die? */
        /* more templates can be added here to support other editors */
        };
        char cbuf[80];
        char *tp, **cp;
        tp = cbuf;
        do {
            *tp++ = c = tok_nextc(tok);
        } while (c != EOF && c != '\n' &&
                 (size_t)(tp - cbuf + 1) < sizeof(cbuf));
        *tp = '\0';
        for (cp = tabforms;
             cp < tabforms + sizeof(tabforms)/sizeof(tabforms[0]);
             cp++) {
            if ((tp = strstr(cbuf, *cp))) {
                int newsize = atoi(tp + strlen(*cp));

                if (newsize >= 1 && newsize <= 40) {
                    tok->tabsize = newsize;
                    if (Py_VerboseFlag)
                        PySys_WriteStderr(
                        "Tab size set to %d\n",
                        newsize);
                }
            }
        }
        while (c != EOF && c != '\n')
            c = tok_nextc(tok);
    }