Why use "& 0xff" in CPython when write byte to file, what it does?

Question

such as:

static void w_long(long x, WFILE *p)
{
    w_byte((char)( x      & 0xff), p);
    w_byte((char)((x>> 8) & 0xff), p);
    w_byte((char)((x>>16) & 0xff), p);
    w_byte((char)((x>>24) & 0xff), p);
}

And why the pyc file is unreadable, where is the const text/string ?

Possible duplicate of [What is Bit Masking?](http://stackoverflow.com/questions/10493411/what-is-bit-masking) — Łukasz Rogalski, Jan 18 '17 at 15:58
Your second question is hard to understand. You should be asking a single question per question anyway. — Sven Marnach, Jan 18 '17 at 16:00

Uriel · Answer 1 · 2017-01-18T16:02:12.953

& 0xff takes the last 8 bits (or one byte) from the number. That makes sure you write only one byte at a time to the file (and in that case, uses for little endian byte-order storing).

0xff is 1111 1111 in binary. Executing logical and with it will turn on all the bits that are 1 in x and are within the last 8 bits.

For example:

x = 0010 0100 1001 0111
                         &
              1111 1111
    -------------------
    0000 0000 1001 0111

Why use "& 0xff" in CPython when write byte to file, what it does?

1 Answers1