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Hardware interview practice

Weighted random values without dist

EasyConstrained RandomSystemVerilog

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.

Starting point

Question code

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

Work through one case

Input
uniform raw outcomes: 0, 1, 2
Expected output
mapped values: 1, 2, 2

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

What to cover

Requirements

  1. Call $urandom_range(2, 0) exactly once for each returned value.
  2. Map raw outcome 0 to 1 and raw outcomes 1 and 2 to 2.
  3. Return no value other than 1 or 2.
  4. Explain the exact probability from the three equiprobable raw outcomes.
Continue practicing
ConstraintsPick a weighted random enumConstraintsBias burst lengths by range