Hendrik van Rooyen wrote: > "Gigs_" <[EMAIL PROTECTED]> wrote: > > >> Can someone explain me bitwise expression? >> few examples for every expression will be nice >> >> x << y Left shift >> x >> y Right shift >> x & y Bitwise AND >> x | y Bitwise OR >> x ^ y Bitwise XOR (exclusive OR) >> ~x Bitwise negation > > The short, and possibly weird, but true, answer is: > > If you have to ask this question, you should avoid > using these things. - Think of them as "Advanced Magic" > > But this is unhelpful, so a slightly longer answer is: > > Computer memory is like a long string of flip-flops that can > take on one of two states - "on" or "True" represented normally by > a digit 1, and "off" or "False" - a digit 0. Hence the term binary. > > Binary means "two valued", just like a Bicycle has two wheels. > > These flip-flops are the smallest element of memory, and one > of them is called a "bit". The plural is "bits". "plural" means > "more than one of". > > Eight bits are called a Byte. > Half a Byte is a Nibble - four bits (sometimes spelt Nybble by > people who are trying to be cute). > There is a concept called a "Word" of memory which is ill defined. > Sometimes it is one or two Bytes, sometimes three nibbles, sometimes > four, eight or sixteen bytes - depends on the hardware's bus width. > > No, I am not going to explain what a bus is. > > You can think of a python number as a word of eight bytes long, > and a python string as a number of bytes of arbitrary length. > > I am also not going to explain big and little endian representation. > Yahoo for it. > > Now the logic operators, as applied to nibbles: > > 1110 << 0111 - shifted left, filled with zero from right > (multiply by two - seven to fourteen) > 0010 >> 0100 - shifted right, filled with zero from left > (divide by two - four to two) > 0100 = 0101 & 1110 - true if both bits true, false otherwise > (used for masking, clearing bits) > 1101 = 0101 | 1100 - false if both bits false, true otherwise > (True if either bit true - used to set > bits) > 1001 = 0101 ^ 1100 - true if only one of the bits true, else false > (anything xored with itself is all > zero) > (used to toggle bits, identity > testing) > 1001 ~ 0110 - inversion "not" - not true is false, not > false > is true > > Also yahoo for "Boolean algebra" and "De Morgan" and "IEEE floating point > representation" > > hth - Hendrik > >
hey I know about bit, bits things, just didn't know how to use bitwise expression (didn't try it and didn't know what it means). so I just needed some examples. Now is all clearer thanks to [EMAIL PROTECTED] and Hendrick van Rooyen -- http://mail.python.org/mailman/listinfo/python-list
