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  • Probabilities of a number while using a dist operator

Probabilities of a number while using a dist operator

SystemVerilog 4981
constraint dist 7 systemverilog constraint 1
sfenil1804
sfenil1804
Full Access
10 posts
June 26, 2020 at 10:30 am

I am trying to understand the difference between := and :/

class packet 
  rand bit[7:0] b;
  rand bit[7:0] a;
 
    constraint adist {a dist {0:=9, [1:255]:=1};}
    constraint bdist {b dist {0:/9, [1:255]:/1};}
endclass

What would be the probability of a being 0 and b being 0?
Is the probability of a being 0 = 9/264 and b being 0 = 9/10 ?

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dave_59
dave_59
Forum Moderator
8586 posts
June 26, 2020 at 10:54 am

In reply to sfenil1804:

The difference is whether the weight gets applied to each value in the range (:=), or divided by the number of elements in the range(/:).

You answered your own question.

— Dave Rich, Verification Architect, Siemens EDA

TC_2017
TC_2017
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46 posts
June 26, 2020 at 1:31 pm

In reply to dave_59:

  rand bit [1:0] ab;
 
  constraint c1 { ab dist {0:= 25, 1:= 75}; }
  constraint c2 { ab dist {0:= 50, 1:= 2}; }

Since Values are overlapping ab would still be either 0 OR 1 .
How would the weight be allocated ? Would weights be average ?

dave_59
dave_59
Forum Moderator
8586 posts
June 26, 2020 at 2:58 pm

In reply to TC_2017:

This is not defined in the LRM. See issue 0003758

— Dave Rich, Verification Architect, Siemens EDA

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