Add +verilator+seed, bug1396.

Changes

@@ -4,6 +4,8 @@ The contributors that suggested a given feature are shown in []. Thanks!
 
 * Verilator 4.011 devel
 
+***   Add +verilator+seed, bug1396. [Stan Sokorac]
+
 
 * Verilator 4.010 2019-01-27
 

bin/verilator

@@ -1599,6 +1599,11 @@ When a model was Verilated using "-x-inital unique", sets the
 initialization technique.  0 = Reset to zeros. 1 = Reset to all-ones.  2 =
 Randomize.  See L</"Unknown states">.
 
+=item +verilator+seed+I<value>
+
+For $random and "-x-initial unique", set the random seed value.  If zero or
+not specified picks a value from the system random number generator.
+
 =item +verilator+V
 
 Shows the verbose version, including configuration information.

include/verilated.cpp

@@ -208,6 +208,7 @@ void VL_PRINTF_MT(const char* formatp, ...) VL_MT_SAFE {
 
 Verilated::Serialized::Serialized() {
     s_randReset = 0;
+    s_randSeed = 0;
     s_debug = 0;
     s_calcUnusedSigs = false;
     s_gotFinish = false;
@@ -245,18 +246,25 @@ vluint64_t vl_rand64() VL_MT_SAFE {
     static VL_THREAD_LOCAL bool t_seeded = false;
     static VL_THREAD_LOCAL vluint64_t t_state[2];
     if (VL_UNLIKELY(!t_seeded)) {
-	t_seeded = true;
-	{
-	    VerilatedLockGuard lock(s_mutex);
-            t_state[0] = ((static_cast<vluint64_t>(vl_sys_rand32()) << 32)
-                          ^ (static_cast<vluint64_t>(vl_sys_rand32())));
-            t_state[1] = ((static_cast<vluint64_t>(vl_sys_rand32()) << 32)
-                          ^ (static_cast<vluint64_t>(vl_sys_rand32())));
+        t_seeded = true;
+        {
+            VerilatedLockGuard lock(s_mutex);
+            if (Verilated::randSeed() != 0) {
+                t_state[0] = ((static_cast<vluint64_t>(Verilated::randSeed()) << 32)
+                              ^ (static_cast<vluint64_t>(Verilated::randSeed())));
+                t_state[1] = ((static_cast<vluint64_t>(Verilated::randSeed()) << 32)
+                              ^ (static_cast<vluint64_t>(Verilated::randSeed())));
+            } else {
+                t_state[0] = ((static_cast<vluint64_t>(vl_sys_rand32()) << 32)
+                              ^ (static_cast<vluint64_t>(vl_sys_rand32())));
+                t_state[1] = ((static_cast<vluint64_t>(vl_sys_rand32()) << 32)
+                              ^ (static_cast<vluint64_t>(vl_sys_rand32())));
+            }
             // Fix state as algorithm is slow to randomize if many zeros
             // This causes a loss of ~ 1 bit of seed entropy, no big deal
             if (VL_COUNTONES_I(t_state[0]) < 10) t_state[0] = ~t_state[0];
             if (VL_COUNTONES_I(t_state[1]) < 10) t_state[1] = ~t_state[1];
-	}
+        }
     }
     // Xoroshiro128+ algorithm
     vluint64_t result = t_state[0] + t_state[1];
@@ -1670,6 +1678,10 @@ void Verilated::randReset(int val) VL_MT_SAFE {
     VerilatedLockGuard lock(m_mutex);
     s_s.s_randReset = val;
 }
+void Verilated::randSeed(int val) VL_MT_SAFE {
+    VerilatedLockGuard lock(m_mutex);
+    s_s.s_randSeed = val;
+}
 void Verilated::calcUnusedSigs(bool flag) VL_MT_SAFE {
     VerilatedLockGuard lock(m_mutex);
     s_s.s_calcUnusedSigs = flag;
@@ -1879,6 +1891,9 @@ void VerilatedImp::commandArgVl(const std::string& arg) {
         else if (commandArgVlValue(arg, "+verilator+rand+reset+", value/*ref*/)) {
             Verilated::randReset(atoi(value.c_str()));
         }
+        else if (commandArgVlValue(arg, "+verilator+seed+", value/*ref*/)) {
+            Verilated::randSeed(atoi(value.c_str()));
+        }
         else if (arg == "+verilator+V") {
             versionDump();  // Someday more info too
             VL_FATAL_MT("COMMAND_LINE", 0, "", "Exiting due to command line argument (not an error)");

include/verilated.h

@@ -342,7 +342,8 @@ class Verilated {
 	bool		s_assertOn;		///< Assertions are enabled
         bool		s_fatalOnVpiError;	///< Stop on vpi error/unsupported
         // Slow path
-        int             s_randReset;            ///< Random reset: 0=all 0s, 1=all 1s, 2=random
+        int s_randReset;  ///< Random reset: 0=all 0s, 1=all 1s, 2=random
+        int s_randSeed;  ///< Random seed: 0=random
         Serialized();
         ~Serialized() {}
     } s_s;
@@ -396,6 +397,8 @@ public:
     /// 2 = Randomize all bits
     static void randReset(int val) VL_MT_SAFE;
     static int  randReset() VL_MT_SAFE { return s_s.s_randReset; }  ///< Return randReset value
+    static void randSeed(int val) VL_MT_SAFE;
+    static int  randSeed() VL_MT_SAFE { return s_s.s_randSeed; }  ///< Return randSeed value
 
     /// Enable debug of internal verilated code
     static void debug(int level) VL_MT_SAFE;

test_regress/t/t_runflag_seed.pl

@@ -0,0 +1,27 @@
+#!/usr/bin/perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2003 by Wilson Snyder. This program is free software; you can
+# redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+
+scenarios(vlt_all => 1);
+
+compile(
+    );
+
+execute(
+    all_run_flags => ["+verilator+seed+5 +SEED=fffffff4"],
+    fails => 0,
+    );
+
+execute(
+    all_run_flags => ["+verilator+seed+6 +SEED=fffffff2"],
+    fails => 0,
+    );
+
+ok(1);
+
+1;

test_regress/t/t_runflag_seed.v

@@ -0,0 +1,17 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed into the Public Domain, for any use,
+// without warranty, 2019 by Wilson Snyder.
+
+`define checkh(gotv,expv) do if ((gotv) !== (expv)) begin $write("%%Error: %s:%0d:  got='h%x exp='h%x\n", `__FILE__,`__LINE__, (gotv), (expv)); $stop; end while(0);
+
+module t;
+   initial begin
+      integer r = $random;
+      integer ex;
+      if ($value$plusargs("SEED=%x", ex) !== 1) $stop;
+      `checkh(r, ex);
+      $write("*-* All Finished *-*\n");
+      $finish;
+   end
+endmodule