Source is the name of a TinyInt column in the table.

Source&4<>0 is a method of determining a binary bit's value, in this case the 3rd bit from the right.

Source&4 is a boolean AND operaration using 4 as the mask, so if:

Source = 00000111 (decimal 7)

opcode = &

(mask) = 00000100 (decimal 4)

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yields 00000100

which is not equal to zero therefore the CASE statement would return 1.