In
computer science, a mask is some data that, along with an operation, is used in order to extract information stored elsewhere.The most common mask used, also known as a bitmask, extracts the status of certain bits in a binary string or number (a
bit field or
bit array). For example, if we have the binary string 10011101 and we want to extract the status of the fifth bit counting along from the
most significant bit, we would use a bitmask such as 00001000 and use the
bitwise AND operator. Recalling that 1 AND 1 = 1, with 0 otherwise, we find the status of the fifth bit, since10011101 AND 00001000 = 00001000
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<
programming> A pattern of
binary values which is combined with some value using
bitwise AND with the result that bits in the value in positions where the mask is zero are also set to zero. For example, if, in
C, we want to test if bits 0 or 2 of x are set, we can write
int mask = 5; /* binary 101 */
if (x & mask) ...
A bit mask might also be used to set certain bits using bitwise OR, or to invert them using bitwise
exclusive OR.
(1995-05-12)
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