1,000+ ASIC Interview Questions: SystemVerilog, UVM & RTL

DescriptionQ321

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Q321DVAppleASIC interview problem

Weighted random values without dist

TechniquesDVSystemVerilogRandomizationProbability

DifficultyEasy

TopicConstrained Random

LanguageSystemVerilog

Requirements4 checkpoints

Problem

Write a SystemVerilog function that returns 1 with probability 1/3 and 2 with probability 2/3. Use exactly one $urandom_range call and do not use dist or constraints.

Function headerSystemVerilog

function automatic int weighted_value();
  // Return 1 with probability 1/3 and 2 with probability 2/3.
endfunction

Example input and output

Use this case to check your interpretation

Input

uniform raw outcomes: 0, 1, 2

Output

mapped values: 1, 2, 2

Explanation

One of three equally likely outcomes returns 1, while two return 2, giving exact probabilities 1/3 and 2/3.

Requirements (4)

Call $urandom_range(2, 0) exactly once for each returned value.
Map raw outcome 0 to 1 and raw outcomes 1 and 2 to 2.
Return no value other than 1 or 2.
Explain the exact probability from the three equiprobable raw outcomes.