Understanding the php operators & (ampersand, bitwise and)

& is binary and. If you have a binary value, and you and with another binary value, then the result will be the bitwise and of the two. An example:

  01101010
& 01011001
= 01001000

The rightmost bit is either a 1 (and in that case the number is an odd number) or it is a 0, in which case the number is even. If you & a number with 1, you only look at the least significant bit, and the if checks if the number is a 1 or a 0. As others have mentioned, look at the bitwise operators for info on how they work.

Read More

What is the meaning to start a function with an ampersand

An ampersand before a function name means the function will return a reference to a variable instead of the value.

Returning by reference is useful when you want to use a function to find to which variable a reference should be bound. Do not use return-by-reference to increase performance. The engine will automatically optimize this on its own. Only return references when you have a valid technical reason to do so.

See Returning References.

Read More