If you're using one's compliment (bitwise NOT) to flip all $a's bits, don't forget that you need to use a mask to specify how many bits you expect in your result:<?php gmp_and(gmp_com('1234'), '2047') ?>>> 813 // 01100101101 in binaryI chose 2047 because 1234 is an 11-bit binary number and 2047 is the maximum an 11-bit register can hold:11111111111 (2047)10011010010 (1234)01100101101 (813)