Electronic – what is the meaning of the pipe symbol “|” in front of a variable


I am analysing some verilog code and found something like

wire z = |a & b;

while simultation the code behaves just like

wire z = a & b;

so i was wondering what is the meaning of the | (pipe) symbol? Does it have any impact on the simulation/synthesis?

Best Answer

This is a bit-wise reduction operator. |a & b means you apply a logical OR to all bits of a (producing a single bit) and then do a logical AND of that bit and b. |a has no effect when a is a single bit.

Nevertheless, it's quite common to see bit-wise reduction applied to single bit values. One typical case is auto-generated code where the actual width of a may depend on the configuration. Another possibility is this being legacy code where a once had several bits. When a became a single bit value, this line was still technically correct so the now unneeded reduction operator was left in.