basename

static VALUE
rb_file_s_basename(int argc, VALUE *argv)
{
    VALUE fname, fext, basename;
    const char *name, *p;
    long f, n;
    rb_encoding *enc;

    if (rb_scan_args(argc, argv, "11", &fname, &fext) == 2) {
        rb_encoding *enc;
        StringValue(fext);
        if (!rb_enc_asciicompat(enc = rb_enc_get(fext))) {
            rb_raise(rb_eEncCompatError, "ascii incompatible character encodings: %s",
                     rb_enc_name(enc));
        }
    }
    FilePathStringValue(fname);
    if (!NIL_P(fext)) enc = rb_enc_check(fname, fext);
    else enc = rb_enc_get(fname);
    if ((n = RSTRING_LEN(fname)) == 0 || !*(name = RSTRING_PTR(fname)))
        return rb_str_new_shared(fname);

    p = ruby_enc_find_basename(name, &f, &n, enc);
    if (n >= 0) {
        if (NIL_P(fext)) {
            f = n;
        }
        else {
            rb_encoding *fenc = rb_enc_get(fext);
            const char *fp;
            if (enc != fenc &&
                rb_enc_str_coderange(fext) != ENC_CODERANGE_7BIT) {
                fext = rb_str_conv_enc(fext, fenc, enc);
            }
            fp = StringValueCStr(fext);
            if (!(f = rmext(p, f, n, fp, RSTRING_LEN(fext), enc))) {
                f = n;
            }
            RB_GC_GUARD(fext);
        }
        if (f == RSTRING_LEN(fname)) return rb_str_new_shared(fname);
    }

    basename = rb_str_new(p, f);
    rb_enc_copy(basename, fname);
    OBJ_INFECT(basename, fname);
    return basename;
}