verilator/test_regress/t/t_constraint_dist_range.v

// DESCRIPTION: Verilator: Verilog Test module
//
// This file ONLY is placed under the Creative Commons Public Domain.
// SPDX-FileCopyrightText: 2026 Antmicro
// SPDX-License-Identifier: CC0-1.0

// verilog_format: off
`define stop $stop
`define checkd(gotv,expv) do if ((gotv) !== (expv)) begin $write("%%Error: %s:%0d:  got=%0d exp=%0d\n", `__FILE__,`__LINE__, (gotv), (expv)); `stop; end while(0);
`define check_range(gotv,minv,maxv) do if ((gotv) < (minv) || (gotv) > (maxv)) begin $write("%%Error: %s:%0d:  got=%0d exp=%0d-%0d\n", `__FILE__,`__LINE__, (gotv), (minv), (maxv)); `stop; end while(0);
`define check_tol(gotv,expv) `check_range((gotv), (expv)*(100-TOL_PCT)/100, (expv)*(100+TOL_PCT)/100)
// verilog_format: on

// Scalar: uniform over [0:9] (10% each)
class DistScalarRange;
  rand bit [3:0] x;
  constraint c { x dist {[4'd0:4'd9] := 1}; }
endclass

// Array foreach: uniform over [0:4] (20% each per element)
class DistForeachUniform;
  rand bit [2:0] a[5];
  constraint c { foreach (a[i]) a[i] dist {[3'd0:3'd4] := 1}; }
endclass

// Array foreach: mixed single + range
//   a[i] dist {0 := 5, [1:9] := 1}  total weight = 5+9 = 14
//   0: 5/14 ~= 35.7%,  1..9: 1/14 ~= 7.1% each
class DistForeachMixed;
  rand bit [3:0] a[5];
  constraint c { foreach (a[i]) a[i] dist {4'd0 := 5, [4'd1:4'd9] := 1}; }
endclass

// Scalar signed int: uniform over negative range [-9:0] (10% each)
class DistNegRange;
  rand int x;
  constraint c { x dist {[-9:0] := 1}; }
endclass

// Non-constant unsigned range bounds: uniform over [lo_val:hi_val] = [2:7] (6 values)
class DistVarRangeUnsigned;
  rand bit [3:0] x;
  bit [3:0] lo_val = 4'd2, hi_val = 4'd7;
  constraint c { x dist {[lo_val:hi_val] := 1}; }
endclass

// Mixed const/non-const bounds: lo is constant, hi is a variable [1:hi_val] = [1:7]
class DistMixedBounds;
  rand bit [3:0] x;
  bit [3:0] hi_val = 4'd7;
  constraint c { x dist {[4'd1:hi_val] := 1}; }
endclass

module t;
  parameter int N = 2000; // randomize() calls per test
  parameter int TOL_PCT = 30; // +-% tolerance on expected counts

  initial begin

    // --- T1: scalar uniform [0:9] ---
    // 10 values, expected N/10 each
    begin
      automatic DistScalarRange obj = new();
      int cnt[10];
      foreach (cnt[v]) cnt[v] = 0;
      repeat (N) begin
        `checkd(obj.randomize(), 1)
        if (obj.x > 4'd9) begin
          $write("%%Error: x=%0d outside valid range [0:9]\n", obj.x);
          `stop;
        end
        cnt[obj.x]++;
      end
      foreach (cnt[v])
        `check_tol(cnt[v], N/10)
    end

    // --- T2: array foreach uniform [0:4], 5 elements * N calls ---
    // total element samples = N*5; 5 values -> expected N each
    begin
      automatic DistForeachUniform obj = new();
      int cnt[5];
      foreach (cnt[v]) cnt[v] = 0;
      repeat (N) begin
        `checkd(obj.randomize(), 1)
        foreach (obj.a[i]) begin
          if (obj.a[i] > 3'd4) begin
            $write("%%Error: a[%0d]=%0d outside valid range [0:4]\n", i, obj.a[i]);
            `stop;
          end
          cnt[obj.a[i]]++;
        end
      end
      foreach (cnt[v])
        `check_tol(cnt[v], N)
    end

    // --- T3: array foreach mixed {0:=5, [1:9]:=1}, 5 elements * N calls ---
    // total element samples = N*5; total weight = 5+9 = 14
    // v=0:    expected N*5*5/14
    // v=1..9: expected N*5*1/14
    begin
      automatic DistForeachMixed obj = new();
      int cnt[10];
      foreach (cnt[v]) cnt[v] = 0;
      repeat (N) begin
        `checkd(obj.randomize(), 1)
        foreach (obj.a[i]) begin
          if (obj.a[i] > 4'd9) begin
            $write("%%Error: a[%0d]=%0d outside valid range [0:9]\n", i, obj.a[i]);
            `stop;
          end
          cnt[obj.a[i]]++;
        end
      end
      `check_tol(cnt[0], N*5*5/14)
      for (int v = 1; v <= 9; v++)
        `check_tol(cnt[v], N*5*1/14)
    end

    // --- T4: signed int, uniform over negative range [-9:0] ---
    // 10 values, expected N/10 each
    // cnt[v] = count of (x == v-9), so v=0 -> x=-9, v=9 -> x=0
    begin
      automatic DistNegRange obj = new();
      int cnt[10];
      foreach (cnt[v]) cnt[v] = 0;
      repeat (N) begin
        `checkd(obj.randomize(), 1)
        if (obj.x < -9 || obj.x > 0) begin
          $write("%%Error: x=%0d outside valid range [-9:0]\n", obj.x);
          `stop;
        end
        cnt[obj.x + 9]++;
      end
      foreach (cnt[v])
        `check_tol(cnt[v], N/10)
    end

    // --- T5: non-constant unsigned range bounds [lo_val:hi_val] = [2:7] ---
    // 6 values, expected N/6 each
    begin
      automatic DistVarRangeUnsigned obj = new();
      int cnt[16];
      foreach (cnt[v]) cnt[v] = 0;
      repeat (N) begin
        `checkd(obj.randomize(), 1)
        if (obj.x < 4'd2 || obj.x > 4'd7) begin
          $write("%%Error: x=%0d outside valid range [2:7]\n", obj.x);
          `stop;
        end
        cnt[obj.x]++;
      end
      for (int v = 2; v <= 7; v++)
        `check_tol(cnt[v], N/6)
    end

    // --- T6: mixed const/non-const bounds [4'd1:hi_val] = [1:7] ---
    // 7 values, expected N/7 each
    begin
      automatic DistMixedBounds obj = new();
      int cnt[16];
      foreach (cnt[v]) cnt[v] = 0;
      repeat (N) begin
        `checkd(obj.randomize(), 1)
        if (obj.x < 4'd1 || obj.x > 4'd7) begin
          $write("%%Error: x=%0d outside valid range [1:7]\n", obj.x);
          `stop;
        end
        cnt[obj.x]++;
      end
      for (int v = 1; v <= 7; v++)
        `check_tol(cnt[v], N/7)
    end

    $write("*-* All Finished *-*\n");
    $finish;
  end
endmodule