iverilog/docs/randomize.md

Unconstrained randomize() / rand (Tier A #6, first slice)

Status: partial — unconstrained integral rand/randc only; no constraint solver.

Supported in this slice

class pkt;
  rand bit [7:0] a;
  rand bit [3:0] b;
  bit [7:0] c;              // non-rand left alone
  function new(); c = 8'h11; endfunction
endclass

pkt p = new;
bit ok = p.randomize();     // returns 1; assigns random values to a,b

• obj.randomize() returns 1 on success (null / unknown class type → 0)
• Assigns random 0/1 bits to all rand and randc integral (bit/logic/reg packed) instance properties
• Non-rand properties are unchanged
• randc is treated like rand for now (no cyclic guarantee)

Encoding

Layer	Role
Parse	rand/randc already property qualifiers; constraint / randomize() with remain sorry
Elab	obj.randomize() → $ivl_randomize(obj) (expr or task)
Target API	ivl_type_prop_rand() exposes qualifiers to codegen
Codegen	%urandom <wid> + %store/prop/v per rand property
Runtime	%urandom fills vec4 with RNG bits (std::mt19937)

Deferred (do not claim)

• Constraint blocks / solver
• randomize() with { ... }
• rand_mode / constraint_mode
• True randc cyclic behavior
• Randomizing non-integral properties (reals, strings, class handles, arrays)
• std::randomize procedural form / inline constraints

Example

examples/randomize/randomize_basic.sv — prints PASSED.

./install/bin/iverilog -g2012 -o /tmp/rand.vvp examples/randomize/randomize_basic.sv
./install/bin/vvp /tmp/rand.vvp

See also STATUS.md and ROADMAP.md.