Do If else have priority in verilog?

Question

I have some query about the priority of if else in verilog. For example.

  If (a)
  b
  else if c
  d
  else if e
  f
  else 
  g

At here, those a,b,c...g are all searched ? How do those have priorities in if~else in verilog?

What do you mean by 'searched'? There's no precedence, or at least it depends on what b,d,f,g are. — Vladimir Cravero, May 19 '15 at 8:25
They're all synthesised, provided a/c/e aren't compile-time constants. — pjc50, May 19 '15 at 8:46
Well. I beg to differ. AFAIK (and pls correct me if I'm wrong), if else construct infers a 'Priority routing Network', with the outermost if carrying highest priority. All of it is synthesized using a ladder of multiplexers (2:1 Mux I believe). — Plutonium smuggler, May 19 '15 at 9:46

Plutonium smuggler · Accepted Answer · 2015-05-19 10:29:21Z

7

An if-else construct infers a priority routing network. Following example is taken directly from a verilog book :

if
 (m==n)
r = a + b + c ;
else if (m > n )
r = a - b ;
else
r = c + 1 ;

The circuit is as shown :

enter image description here

As you can see, the outermost if is given a priority in the sense that it is routed first if a match is found, bypassing others.

answered May 19 '15 at 10:10

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\$\begingroup\$ Thanks . There are priorities in there as cuicuit. First m and n equality check then m and n size check. \$\endgroup\$ – gmotree May 19 '15 at 10:17
\$\begingroup\$ Yes. And finally a default case when none of the above exists. \$\endgroup\$ – Plutonium smuggler May 19 '15 at 10:21
\$\begingroup\$ Mind giving a reference to the book? \$\endgroup\$ – Dzarda May 19 '15 at 10:25
\$\begingroup\$ Added the link to the book. \$\endgroup\$ – Plutonium smuggler May 19 '15 at 10:29
\$\begingroup\$ Should the synthesis tool recognize the three cases as mutually exclusive and be able to do one parallell mux? \$\endgroup\$ – Moberg Dec 3 '19 at 22:19

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