2
\$\begingroup\$

In the following code, I attempt to randomize the transaction which contains a dynamic array 'PhyRB', with the constraint that each element in the array is less than 'ResBlks' value. Please note that both 'PhyRB' array and 'ResBlks' are of unsigned (bit [6:0]) type:

module tb;

typedef enum logic {Type2=0, Sorted=1} PhyRBAlloc_t; // RBs allocation type

class Txn;
  rand bit [6:0] ResBlks; // Number of resource blocks (NRB)
  rand PhyRBAlloc_t PhyRBAllocType; // Physical RB allocation type
  rand bit [6:0] PhyRB[2][]; // Physical RB mapping

  // Array of unique values
  constraint ArrSize {
    PhyRB[0].size() > 0;
    PhyRB[0].size() <= ResBlks;
    PhyRB[1].size() == PhyRB[0].size();
  }
  constraint vals {
    foreach(PhyRB[0][i]) PhyRB[0][i] < ResBlks;
    if(PhyRBAllocType == Type2) {
      foreach(PhyRB[1][i]) PhyRB[1][i] < ResBlks;
    }
    unique { PhyRB[0] };
    unique { PhyRB[1] } ;
  }

  constraint ResBlksConstraint {
    ResBlks inside {6,15,25,50,75,100};
  }

  function void post_randomize;
    if(PhyRBAllocType == Sorted) begin
      PhyRB[0].sort();
      PhyRB[1] = PhyRB[0];
    end
  endfunction

endclass

initial begin
  Txn txn;
  txn = new;

  txn.ResBlks = 50;
  txn.ResBlks.rand_mode(0);
  if(!txn.randomize())
    $error("txn rand failed");

  if(!txn.randomize(PhyRBAllocType))
    $error("PhyRBAllocType rand failed");
  if(!txn.randomize(PhyRB))
    $error("PhyRB rand failed");
  
  $info($sformatf("UsedRBNum: %0d", txn.PhyRB[0].size()));
  $info($sformatf("RB allocation: %s", txn.PhyRBAllocType.name()));
  $info($sformatf("PhyRB[0]: %0p", txn.PhyRB[0]));
  $info($sformatf("PhyRB[1]: %0p", txn.PhyRB[1]));
end

endmodule

The randomization reports to be successful, yet the values of 'PhyRB' elements do not meet the constraint. Although 'ResBlks' value is 50, yet some elements have values greater than 50:

# ** Info: PhyRB[0]: 3 4 8 9 12 17 19 21 22 25 29 36 38 45 46 47 48 61 
                     68 71 76 81 86 91 97 99 101 104 115 124 126
# ** Info: PhyRB[1]: 3 4 8 9 12 17 19 21 22 25 29 36 38 45 46 47 48 61 
                     68 71 76 81 86 91 97 99 101 104 115 124 126

I tried to run QuestaSim with the -solvedebug option, so it reports the following:


# Start class::randomize#1 @ 0ns: t2.sv(44)
# -> type=Txn, randstate=MSd1ef12ef321778f006bc6d297504e6e2
# 
# Begin RandSet 1
# Random Variables:
#   bit signed [31:0] PhyRB[1].size
#   bit signed [31:0] PhyRB[0].size
# Constraints:
#   t2.sv(12): ArrSize { (PhyRB[0].size > 0); }
#   t2.sv(13): ArrSize { (PhyRB[0].size <= ResBlks); }
#   t2.sv(14): ArrSize { (PhyRB[1].size == PhyRB[0].size); }
#   t2.sv(8): (PhyRB[1].size >= 0);
#   t2.sv(8): (PhyRB[0].size >= 0);
# * Solving RandSet 1 with ACT engine
# Solved: PhyRB[0].size = 29
# Solved: PhyRB[1].size = 29
# End RandSet 1
# 
# Begin RandSet 2
# Random Variables:
#   bit [6:0] PhyRB[0][0]
#   bit [6:0] PhyRB[0][1]
#   bit [6:0] PhyRB[0][2]
#   bit [6:0] PhyRB[0][3]
#   bit [6:0] PhyRB[0][4]
#   bit [6:0] PhyRB[0][5]
#   bit [6:0] PhyRB[0][6]
#   bit [6:0] PhyRB[0][7]
#   bit [6:0] PhyRB[0][8]
#   bit [6:0] PhyRB[0][9]
#   bit [6:0] PhyRB[0][10]
#   bit [6:0] PhyRB[0][11]
#   bit [6:0] PhyRB[0][12]
#   bit [6:0] PhyRB[0][13]
#   bit [6:0] PhyRB[0][14]
#   bit [6:0] PhyRB[0][15]
#   bit [6:0] PhyRB[0][16]
#   bit [6:0] PhyRB[0][17]
#   bit [6:0] PhyRB[0][18]
#   bit [6:0] PhyRB[0][19]
#   bit [6:0] PhyRB[0][20]
#   bit [6:0] PhyRB[0][21]
#   bit [6:0] PhyRB[0][22]
#   bit [6:0] PhyRB[0][23]
#   bit [6:0] PhyRB[0][24]
#   bit [6:0] PhyRB[0][25]
#   bit [6:0] PhyRB[0][26]
#   bit [6:0] PhyRB[0][28]
#   bit [6:0] PhyRB[0][27]
# Constraints:
#   t2.sv(21): vals { unique {PhyRB[0]}; }
#   t2.sv(17): vals { (PhyRB[0][0] < ResBlks); }
#   t2.sv(17): vals { (PhyRB[0][1] < ResBlks); }
#   t2.sv(17): vals { (PhyRB[0][2] < ResBlks); }
#   t2.sv(17): vals { (PhyRB[0][3] < ResBlks); }
#   t2.sv(17): vals { (PhyRB[0][4] < ResBlks); }
#   t2.sv(17): vals { (PhyRB[0][5] < ResBlks); }
#   t2.sv(17): vals { (PhyRB[0][6] < ResBlks); }
# * Solving RandSet 2 with ACT engine
# Solved: PhyRB[0][11] = 7'h21
# Solved: PhyRB[0][15] = 7'h64
# Solved: PhyRB[0][1] = 7'h1d
# Solved: PhyRB[0][28] = 7'h26
# Solved: PhyRB[0][22] = 7'h48
# Solved: PhyRB[0][26] = 7'h66
# Solved: PhyRB[0][17] = 7'h3a
# Solved: PhyRB[0][9] = 7'h41
# Solved: PhyRB[0][14] = 7'h54
# Solved: PhyRB[0][27] = 7'h28
# Solved: PhyRB[0][16] = 7'h35
# Solved: PhyRB[0][5] = 7'h2b
# Solved: PhyRB[0][18] = 7'h27
# Solved: PhyRB[0][24] = 7'h42
# Solved: PhyRB[0][20] = 7'h00
# Solved: PhyRB[0][0] = 7'h24
# Solved: PhyRB[0][4] = 7'h2c
# Solved: PhyRB[0][19] = 7'h56
# Solved: PhyRB[0][8] = 7'h70
# Solved: PhyRB[0][6] = 7'h12
# Solved: PhyRB[0][21] = 7'h0c
# Solved: PhyRB[0][23] = 7'h7c
# Solved: PhyRB[0][25] = 7'h71
# Solved: PhyRB[0][10] = 7'h6e
# Solved: PhyRB[0][7] = 7'h3e
# Solved: PhyRB[0][3] = 7'h1f
# Solved: PhyRB[0][12] = 7'h11
# Solved: PhyRB[0][13] = 7'h03
# Solved: PhyRB[0][2] = 7'h09
# End RandSet 2
# 
# Begin RandSet 3
# Random Variables:
#   bit [6:0] PhyRB[1][6]
#   reg [0:0] PhyRBAllocType
#   bit [6:0] PhyRB[1][5]
#   bit [6:0] PhyRB[1][4]
#   bit [6:0] PhyRB[1][3]
#   bit [6:0] PhyRB[1][2]
#   bit [6:0] PhyRB[1][1]
#   bit [6:0] PhyRB[1][0]
#   bit [6:0] PhyRB[1][7]
#   bit [6:0] PhyRB[1][8]
#   bit [6:0] PhyRB[1][9]
#   bit [6:0] PhyRB[1][10]
#   bit [6:0] PhyRB[1][11]
#   bit [6:0] PhyRB[1][12]
#   bit [6:0] PhyRB[1][13]
#   bit [6:0] PhyRB[1][14]
#   bit [6:0] PhyRB[1][15]
#   bit [6:0] PhyRB[1][16]
#   bit [6:0] PhyRB[1][17]
#   bit [6:0] PhyRB[1][18]
#   bit [6:0] PhyRB[1][19]
#   bit [6:0] PhyRB[1][20]
#   bit [6:0] PhyRB[1][21]
#   bit [6:0] PhyRB[1][22]
#   bit [6:0] PhyRB[1][23]
#   bit [6:0] PhyRB[1][24]
#   bit [6:0] PhyRB[1][25]
#   bit [6:0] PhyRB[1][26]
#   bit [6:0] PhyRB[1][28]
#   bit [6:0] PhyRB[1][27]
# Constraints:
#   t2.sv(22): vals { unique {PhyRB[1]}; }
#   t2.sv(7): (PhyRBAllocType inside { [Type2:Sorted] });
#   t2.sv(19): vals { if ((~PhyRBAllocType)) {(PhyRB[1][6] < ResBlks);} }
#   t2.sv(19): vals { if ((~PhyRBAllocType)) {(PhyRB[1][5] < ResBlks);} }
#   t2.sv(19): vals { if ((~PhyRBAllocType)) {(PhyRB[1][4] < ResBlks);} }
#   t2.sv(19): vals { if ((~PhyRBAllocType)) {(PhyRB[1][3] < ResBlks);} }
#   t2.sv(19): vals { if ((~PhyRBAllocType)) {(PhyRB[1][2] < ResBlks);} }
#   t2.sv(19): vals { if ((~PhyRBAllocType)) {(PhyRB[1][1] < ResBlks);} }
#   t2.sv(19): vals { if ((~PhyRBAllocType)) {(PhyRB[1][0] < ResBlks);} }
# * Solving RandSet 3 with ACT engine
# Solved: PhyRBAllocType = Sorted
# Solved: PhyRB[1][12] = 7'h66
# Solved: PhyRB[1][15] = 7'h2b
# Solved: PhyRB[1][19] = 7'h19
# Solved: PhyRB[1][3] = 7'h11
# Solved: PhyRB[1][13] = 7'h75
# Solved: PhyRB[1][27] = 7'h4f
# Solved: PhyRB[1][0] = 7'h3e
# Solved: PhyRB[1][21] = 7'h48
# Solved: PhyRB[1][9] = 7'h46
# Solved: PhyRB[1][10] = 7'h2c
# Solved: PhyRB[1][11] = 7'h29
# Solved: PhyRB[1][24] = 7'h45
# Solved: PhyRB[1][7] = 7'h72
# Solved: PhyRB[1][8] = 7'h4e
# Solved: PhyRB[1][26] = 7'h60
# Solved: PhyRB[1][2] = 7'h43
# Solved: PhyRB[1][14] = 7'h09
# Solved: PhyRB[1][20] = 7'h0d
# Solved: PhyRB[1][4] = 7'h5d
# Solved: PhyRB[1][28] = 7'h69
# Solved: PhyRB[1][5] = 7'h6a
# Solved: PhyRB[1][6] = 7'h39
# Solved: PhyRB[1][1] = 7'h28
# Solved: PhyRB[1][18] = 7'h12
# Solved: PhyRB[1][17] = 7'h79
# Solved: PhyRB[1][25] = 7'h15
# Solved: PhyRB[1][23] = 7'h7c
# Solved: PhyRB[1][22] = 7'h44
# Solved: PhyRB[1][16] = 7'h6e
# End RandSet 3
# 
# v-- executing $rand.post_randomize() [type=Txn: t2.sv(29)]
# --^ $rand.post_randomize() done
# 
# End class::randomize#1 @ 0ns: t2.sv(44)
# -> result=1
# 
# Start class::randomize#2 @ 0ns: t2.sv(47)
# -> type=Txn, randstate=MS321778f0420665ba7797d1d1e04a9cc9
# 
# Executing function:
#   t2.sv(14): function()
# 
# Executing function:
#   t2.sv(14): function()
# 
# Executing function:
#   t2.sv(13): function()
# 
# Executing function:
#   t2.sv(12): function()
# 
# Begin RandSet 4
# Random Variables:
#   reg [0:0] PhyRBAllocType
# Constraints:
#   t2.sv(7): (PhyRBAllocType inside { [Type2:Sorted] });
# * Solving RandSet 4 with Limit engine
# Solved: PhyRBAllocType = Sorted
# End RandSet 4
# 
# v-- executing $rand.post_randomize() [type=Txn: t2.sv(29)]
# --^ $rand.post_randomize() done
# 
# End class::randomize#2 @ 0ns: t2.sv(47)
# -> result=1
# 
# Start class::randomize#3 @ 0ns: t2.sv(49)
# -> type=Txn, randstate=MS420665ba7797d1d19a9755ad98e48700
# 
# Begin RandSet 5
# Random Variables:
#   bit signed [31:0] PhyRB[1].size
#   bit signed [31:0] PhyRB[0].size
# Constraints:
#   t2.sv(12): ArrSize { (PhyRB[0].size > 0); }
#   t2.sv(13): ArrSize { (PhyRB[0].size <= ResBlks); }
#   t2.sv(14): ArrSize { (PhyRB[1].size == PhyRB[0].size); }
#   t2.sv(8): (PhyRB[1].size >= 0);
#   t2.sv(8): (PhyRB[0].size >= 0);
# * Solving RandSet 5 with ACT engine
# Solved: PhyRB[0].size = 31
# Solved: PhyRB[1].size = 31
# End RandSet 5
# 
# Begin RandSet 6
# Random Variables:
#   bit [6:0] PhyRB[0][0]
#   bit [6:0] PhyRB[0][1]
#   bit [6:0] PhyRB[0][2]
#   bit [6:0] PhyRB[0][3]
#   bit [6:0] PhyRB[0][4]
#   bit [6:0] PhyRB[0][5]
#   bit [6:0] PhyRB[0][6]
#   bit [6:0] PhyRB[0][7]
#   bit [6:0] PhyRB[0][8]
#   bit [6:0] PhyRB[0][9]
#   bit [6:0] PhyRB[0][10]
#   bit [6:0] PhyRB[0][11]
#   bit [6:0] PhyRB[0][12]
#   bit [6:0] PhyRB[0][13]
#   bit [6:0] PhyRB[0][14]
#   bit [6:0] PhyRB[0][15]
#   bit [6:0] PhyRB[0][16]
#   bit [6:0] PhyRB[0][17]
#   bit [6:0] PhyRB[0][18]
#   bit [6:0] PhyRB[0][19]
#   bit [6:0] PhyRB[0][20]
#   bit [6:0] PhyRB[0][21]
#   bit [6:0] PhyRB[0][22]
#   bit [6:0] PhyRB[0][23]
#   bit [6:0] PhyRB[0][24]
#   bit [6:0] PhyRB[0][25]
#   bit [6:0] PhyRB[0][26]
#   bit [6:0] PhyRB[0][27]
#   bit [6:0] PhyRB[0][28]
#   bit [6:0] PhyRB[0][30]
#   bit [6:0] PhyRB[0][29]
# Constraints:
#   t2.sv(21): vals { unique {PhyRB[0]}; }
#   t2.sv(17): vals { (PhyRB[0][0] < ResBlks); }
#   t2.sv(17): vals { (PhyRB[0][1] < ResBlks); }
#   t2.sv(17): vals { (PhyRB[0][2] < ResBlks); }
#   t2.sv(17): vals { (PhyRB[0][3] < ResBlks); }
#   t2.sv(17): vals { (PhyRB[0][4] < ResBlks); }
#   t2.sv(17): vals { (PhyRB[0][5] < ResBlks); }
#   t2.sv(17): vals { (PhyRB[0][6] < ResBlks); }
# * Solving RandSet 6 with ACT engine
# Solved: PhyRB[0][20] = 7'h47
# Solved: PhyRB[0][18] = 7'h24
# Solved: PhyRB[0][12] = 7'h44
# Solved: PhyRB[0][1] = 7'h2e
# Solved: PhyRB[0][17] = 7'h65
# Solved: PhyRB[0][3] = 7'h16
# Solved: PhyRB[0][27] = 7'h2f
# Solved: PhyRB[0][14] = 7'h1d
# Solved: PhyRB[0][15] = 7'h4c
# Solved: PhyRB[0][30] = 7'h08
# Solved: PhyRB[0][22] = 7'h15
# Solved: PhyRB[0][9] = 7'h04
# Solved: PhyRB[0][21] = 7'h61
# Solved: PhyRB[0][23] = 7'h09
# Solved: PhyRB[0][26] = 7'h56
# Solved: PhyRB[0][25] = 7'h5b
# Solved: PhyRB[0][28] = 7'h7e
# Solved: PhyRB[0][2] = 7'h19
# Solved: PhyRB[0][7] = 7'h63
# Solved: PhyRB[0][13] = 7'h73
# Solved: PhyRB[0][16] = 7'h13
# Solved: PhyRB[0][6] = 7'h2d
# Solved: PhyRB[0][8] = 7'h3d
# Solved: PhyRB[0][24] = 7'h7c
# Solved: PhyRB[0][11] = 7'h51
# Solved: PhyRB[0][4] = 7'h03
# Solved: PhyRB[0][29] = 7'h26
# Solved: PhyRB[0][10] = 7'h30
# Solved: PhyRB[0][0] = 7'h0c
# Solved: PhyRB[0][19] = 7'h68
# Solved: PhyRB[0][5] = 7'h11
# End RandSet 6
# 
# Begin RandSet 7
# Random Variables:
#   bit [6:0] PhyRB[1][0]
#   bit [6:0] PhyRB[1][1]
#   bit [6:0] PhyRB[1][2]
#   bit [6:0] PhyRB[1][3]
#   bit [6:0] PhyRB[1][4]
#   bit [6:0] PhyRB[1][5]
#   bit [6:0] PhyRB[1][6]
#   bit [6:0] PhyRB[1][7]
#   bit [6:0] PhyRB[1][8]
#   bit [6:0] PhyRB[1][9]
#   bit [6:0] PhyRB[1][10]
#   bit [6:0] PhyRB[1][11]
#   bit [6:0] PhyRB[1][12]
#   bit [6:0] PhyRB[1][13]
#   bit [6:0] PhyRB[1][14]
#   bit [6:0] PhyRB[1][15]
#   bit [6:0] PhyRB[1][16]
#   bit [6:0] PhyRB[1][17]
#   bit [6:0] PhyRB[1][18]
#   bit [6:0] PhyRB[1][19]
#   bit [6:0] PhyRB[1][20]
#   bit [6:0] PhyRB[1][21]
#   bit [6:0] PhyRB[1][22]
#   bit [6:0] PhyRB[1][23]
#   bit [6:0] PhyRB[1][24]
#   bit [6:0] PhyRB[1][25]
#   bit [6:0] PhyRB[1][26]
#   bit [6:0] PhyRB[1][27]
#   bit [6:0] PhyRB[1][28]
#   bit [6:0] PhyRB[1][30]
#   bit [6:0] PhyRB[1][29]
# Constraints:
#   t2.sv(22): vals { unique {PhyRB[1]}; }
# * Solving RandSet 7 with ACT engine
# Solved: PhyRB[1][9] = 7'h12
# Solved: PhyRB[1][28] = 7'h59
# Solved: PhyRB[1][14] = 7'h2d
# Solved: PhyRB[1][3] = 7'h27
# Solved: PhyRB[1][11] = 7'h2b
# Solved: PhyRB[1][29] = 7'h17
# Solved: PhyRB[1][18] = 7'h45
# Solved: PhyRB[1][26] = 7'h0a
# Solved: PhyRB[1][27] = 7'h76
# Solved: PhyRB[1][20] = 7'h5c
# Solved: PhyRB[1][10] = 7'h28
# Solved: PhyRB[1][12] = 7'h4f
# Solved: PhyRB[1][6] = 7'h13
# Solved: PhyRB[1][8] = 7'h66
# Solved: PhyRB[1][4] = 7'h18
# Solved: PhyRB[1][7] = 7'h1e
# Solved: PhyRB[1][30] = 7'h14
# Solved: PhyRB[1][23] = 7'h44
# Solved: PhyRB[1][0] = 7'h47
# Solved: PhyRB[1][13] = 7'h50
# Solved: PhyRB[1][22] = 7'h3c
# Solved: PhyRB[1][25] = 7'h16
# Solved: PhyRB[1][24] = 7'h5a
# Solved: PhyRB[1][21] = 7'h24
# Solved: PhyRB[1][16] = 7'h33
# Solved: PhyRB[1][5] = 7'h46
# Solved: PhyRB[1][19] = 7'h56
# Solved: PhyRB[1][2] = 7'h4c
# Solved: PhyRB[1][17] = 7'h0c
# Solved: PhyRB[1][15] = 7'h5d
# Solved: PhyRB[1][1] = 7'h08
# End RandSet 7
# 
# Unconstrained Random Variables:
# Solved: PhyRB[0][?] = 7'h75
# Solved: PhyRB[0][?] = 7'h39
# Solved: PhyRB[0][?] = 7'h30
# Solved: PhyRB[0][?] = 7'h6c
# Solved: PhyRB[0][?] = 7'h74
# Solved: PhyRB[0][?] = 7'h09
# Solved: PhyRB[0][?] = 7'h1a
# Solved: PhyRB[0][?] = 7'h3d
# Solved: PhyRB[0][?] = 7'h3c
# Solved: PhyRB[0][?] = 7'h71
# Solved: PhyRB[0][?] = 7'h43
# Solved: PhyRB[0][?] = 7'h01
# Solved: PhyRB[0][?] = 7'h34
# Solved: PhyRB[0][?] = 7'h76
# Solved: PhyRB[0][?] = 7'h68
# Solved: PhyRB[0][?] = 7'h6a
# Solved: PhyRB[0][?] = 7'h74
# Solved: PhyRB[0][?] = 7'h5c
# Solved: PhyRB[0][?] = 7'h17
# Solved: PhyRB[0][?] = 7'h12
# Solved: PhyRB[0][?] = 7'h03
# Solved: PhyRB[0][?] = 7'h05
# Solved: PhyRB[0][?] = 7'h2b
# Solved: PhyRB[0][?] = 7'h44
# Solved: PhyRB[0][?] = 7'h78
# Solved: PhyRB[0][?] = 7'h1f
# Solved: PhyRB[0][?] = 7'h15
# Solved: PhyRB[0][?] = 7'h2d
# Solved: PhyRB[0][?] = 7'h22
# Solved: PhyRB[1][?] = 7'h4c
# Solved: PhyRB[1][?] = 7'h33
# Solved: PhyRB[1][?] = 7'h37
# Solved: PhyRB[1][?] = 7'h11
# Solved: PhyRB[1][?] = 7'h2e
# Solved: PhyRB[1][?] = 7'h72
# Solved: PhyRB[1][?] = 7'h06
# Solved: PhyRB[1][?] = 7'h22
# Solved: PhyRB[1][?] = 7'h53
# Solved: PhyRB[1][?] = 7'h5b
# Solved: PhyRB[1][?] = 7'h66
# Solved: PhyRB[1][?] = 7'h33
# Solved: PhyRB[1][?] = 7'h77
# Solved: PhyRB[1][?] = 7'h26
# Solved: PhyRB[1][?] = 7'h00
# Solved: PhyRB[1][?] = 7'h0f
# Solved: PhyRB[1][?] = 7'h7e
# Solved: PhyRB[1][?] = 7'h65
# Solved: PhyRB[1][?] = 7'h57
# Solved: PhyRB[1][?] = 7'h26
# Solved: PhyRB[1][?] = 7'h3b
# Solved: PhyRB[1][?] = 7'h36
# Solved: PhyRB[1][?] = 7'h74
# Solved: PhyRB[1][?] = 7'h57
# Solved: PhyRB[1][?] = 7'h67
# Solved: PhyRB[1][?] = 7'h35
# Solved: PhyRB[1][?] = 7'h7a
# Solved: PhyRB[1][?] = 7'h31
# Solved: PhyRB[1][?] = 7'h00
# 
# v-- executing $rand.post_randomize() [type=Txn: t2.sv(29)]
# --^ $rand.post_randomize() done
# 
# End class::randomize#3 @ 0ns: t2.sv(49)
# -> result=1

I am running the QuestaSim 10.4c simulation tool.

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2 Answers 2

Reset to default
2
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The problem is in the foreach syntax, it should be:

foreach PhyRB[,i] PhyRB[0][i] < ResBlks;
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1
  • \$\begingroup\$ This code has a syntax error on newer versions of questasim (for example, Mentor Questa 2021.3 on EDA Playground). It is also a syntax error on the other simulators there. \$\endgroup\$
    – toolic
    Commented Jul 4, 2023 at 15:45
0
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That behavior is probably a bug in QuestaSim version 10.4c. Your code behaves as expected on a newer version of Mentor Questa 2021.3 on EDA Playground.

Allowing the randomization to occur several times, the values of the array are always less than 50, adhering to the constraints. The code also runs on other simulators, and the results are as expected.

Note that this answer is posted a few years after the question. It is reasonable to assume that bugs have been fixed in the simulator since that time.

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