关于Verilog中"= |"语法含义及相关代码逻辑的技术问询

Hey there! Let's clear up this confusion step by step—you're mixing up two totally different Verilog constructs here, so let's break it down nicely.

First: What does the = | actually mean in your code? #

In the line assign result = | pterms;, the | isn't paired with the = as a single operator. Instead, | pterms is a unary reduction OR operator—a handy Verilog shortcut to OR all bits of a vector together into a single bit.

Let's unpack your code snippet: #

wire result; 
wire [NUM_BITS-1:0] pterms; 
assign result = | pterms;

Here's exactly what's happening:

• pterms is a vector of NUM_BITS bits (for example, if NUM_BITS=4, it's a 4-bit wire).
• The unary | takes every bit in pterms, runs an OR operation across all of them, and spits out a 1-bit result.
• That 1-bit result gets assigned directly to result.

In plain terms: result will be 1 if any bit in pterms is 1. It will only be 0 if every single bit in pterms is 0.

For quick examples:

• If pterms = 4'b1001, then |pterms = 1 | 0 | 0 | 1 = 1'b1
• If pterms = 4'b0000, then |pterms = 0 | 0 | 0 | 0 = 1'b0

Correcting your misunderstanding #

You asked if this is equivalent to assign result = result | pterms—that's not right at all, and here's why:

1. It creates a combinational loop: Assigning result to itself in a combinational assign creates a feedback path, which is almost always a bug. Synthesis tools will throw errors here because it's not valid combinational logic.
2. It doesn't target just pterms[0]: Even if you wrote that line (which you shouldn't), Verilog would first zero-extend the 1-bit result to match the width of pterms, then do a bitwise OR between each extended bit of result and the corresponding bit of pterms. Finally, it would truncate that wide result back to 1 bit to fit result—this is nothing like the clean reduction OR operation in your original code.

So to recap: The original line is a simple, efficient way to check if any bit in a vector is high—no bugs, no messy loops, just standard Verilog syntax doing its job.

内容的提问来源于stack exchange，提问作者stackoverflow_user