add_char
add_char(out, idx, len, replace_chars[q - quotable_chars]);
add_char(out, idx, len, '\\');
add_char(out, idx, len, replace_chars[q - quotable_chars]);
add_char(out, idx, len, *p);
add_char(name, idx, len, '/');
add_char(name, idx, len, '@');
#define atomic_add_char ATOMIC_SAN(add_char)
rv = add_char(curchar, map_idx, bytes,
rv = add_char(curchar, map_idx, bytes,