rb_econv_putback  340 include/ruby/encoding.h void rb_econv_putback(rb_econv_t *ec, unsigned char *p, int n);
rb_econv_putback 2273 io.c                       rb_econv_putback(fptr->readconv, (unsigned char *)fptr->rbuf.ptr + fptr->rbuf.off - putbackable, putbackable);
rb_econv_putback 4121 transcode.c        rb_econv_putback(ec, (unsigned char *)RSTRING_PTR(str), n);