# and_bits

Definition: | atom x3 = and_bits(atom x1, atom x2)
Description: | Perform the logical AND operation on corresponding bits in x1 and x2. A bit in x3 will be 1 only if the corresponding bits in x1 and x2 are both 1. Commonly used to test bit settings in a bit-field (see example 1).
pwa/p2js: | Supported.
Comments: | As of 0.8.2+ the infix operator && can be used in place of and_bits(). This function may be applied to an atom or sq_and_bits() to all elements of a sequence. The rules for sequence operations apply. The arguments must be representable as 32-bit numbers, either signed or unsigned. If you intend to manipulate full 32-bit values, you should declare your variables as atom, rather than integer. The integer type is limited to 31-bits. Results are treated as signed numbers. They will be negative when the highest-order bit is 1. Caution: many cryptographic functions and the like require unsigned 32-bit integers, especially when bit-shifting, for which and_bitsu() can be used instead. To understand the binary representation of a number you should display it in hexadecimal notation. Use the %x format of printf().
Example 1: |
    if and_bits(flags,XPAD) then width-=XPADDING end if -- apply width padding
Example 2: |
    a = and_bits(#0F0F0000, #12345678)
    -- a is #02040000
Example 3: |
    s = sq_and_bits(#FF, {#123456, #876543, #2211})
    -- s is {#56, #43, #11}
Example 4: |
    a = and_bits(#FFFFFFFF, #FFFFFFFF)
    -- a is -1
    -- Note that #FFFFFFFF is a positive number,
    -- but the result of a bitwise logical operation is interpreted
    -- as a signed 32-bit number, so it is negative.
Implementation: | pilx86.e emits inline binary directly for two initialised integers, otherwise a call to :%opAndBits in builtins\VM\pMath.e and_bitsu() is currently implemented in builtins/ubits.e (also an autoinclude), though that could probably be improved on, if needed.
See Also: | or_bits, xor_bits, not_bits, int_to_bits