Update RNG to use Borland C++ RNG Routine

MBBSEmu.Tests/ExportedModules/Majorbbs/rand_Tests.cs

@@ -0,0 +1,37 @@
+using System.Collections.Generic;
+using Xunit;
+
+namespace MBBSEmu.Tests.ExportedModules.Majorbbs
+{
+    /// <summary>
+    ///     Tests verified against results from Borland C++ 4.5 for DOS
+    /// </summary>
+    public class rand_Tests : ExportedModuleTestBase
+    {
+        private const int RAND_ORDINAL = 486;
+
+        [Theory]
+        [InlineData(1234, 1356, 2236414843)]
+        [InlineData(2236414843, 29133, 4056779384)]
+        [InlineData(4056779384, 21998, 3589159641)]
+        [InlineData(3589159641, 27018, 1770671342)]
+        [InlineData(1770671342, 30398, 4139675975)]
+        [InlineData(4139675975, 13799, 904336820)]
+        [InlineData(904336820, 26300, 3871102533)]
+        [InlineData(3871102533, 16520, 3230196298)]
+        [InlineData(3230196298, 26957, 1766679891)]
+        [InlineData(1766679891, 21523, 1410548784)]
+        public void srandTest(uint seed, ushort expectedRandom, uint newSeed)
+        {
+            Reset();
+
+            mbbsEmuMemoryCore.SetDWord("RANDSEED", seed);
+
+            ExecuteApiTest(HostProcess.ExportedModules.Majorbbs.Segment, RAND_ORDINAL, new List<ushort>());
+
+            //Verify Results
+            Assert.Equal(expectedRandom, mbbsEmuCpuRegisters.AX);
+            Assert.Equal(newSeed, mbbsEmuMemoryCore.GetDWord("RANDSEED"));
+        }
+    }
+}

MBBSEmu.Tests/ExportedModules/Majorbbs/random_Tests.cs

@@ -69,16 +69,5 @@ public void lngrndTest_invalid()
             //Verify Results
             Assert.Equal(mbbsEmuCpuRegisters.GetLong(), expectedValue);
         }
-
-        [Fact]
-        public void randTest()
-        {
-            Reset();
-
-            ExecuteApiTest(HostProcess.ExportedModules.Majorbbs.Segment,RAND_ORDINAL, new List<ushort>());
-
-            //Verify Results
-            Assert.InRange(mbbsEmuCpuRegisters.AX, 1, 32767);
-        }
     }
 }

MBBSEmu.Tests/ExportedModules/Majorbbs/srand_Tests.cs

@@ -0,0 +1,24 @@
+using System.Collections.Generic;
+using Xunit;
+
+namespace MBBSEmu.Tests.ExportedModules.Majorbbs
+{
+    public class srand_Tests : ExportedModuleTestBase
+    {
+        private const int SRAND_ORDINAL = 561;
+
+        [Theory]
+        [InlineData(0)]
+        [InlineData(1)]
+        [InlineData(ushort.MaxValue)]
+        public void srandTest(ushort seed)
+        {
+            Reset();
+
+            ExecuteApiTest(HostProcess.ExportedModules.Majorbbs.Segment, SRAND_ORDINAL, new List<ushort> { seed });
+
+            //Verify Results
+            Assert.Equal(seed, mbbsEmuMemoryCore.GetDWord("RANDSEED"));
+        }
+    }
+}

MBBSEmu/HostProcess/ExportedModules/Majorbbs.cs

@@ -229,7 +229,8 @@
             Module.Memory.AllocateVariable("TXTVARS", TextvarStruct.Size * MaxTextVariables, true); //Up to 64 Text Variables per Module
             Module.Memory.SetArray("TXTVARS", new TextvarStruct("SYSTEM", new FarPtr(Segment, 9000)).Data); //Set 1st var as SYSTEM variable reference with special pointer
             Module.Memory.AllocateVariable("HDLCON", FarPtr.Size); //Handles the connection for the current User
-
+            Module.Memory.AllocateVariable("RANDSEED", sizeof(uint)); //Seed value for Borland C++ Pseudo-Random Number Generator
+            Module.Memory.SetDWord("RANDSEED", (uint)_random.Next(1, ushort.MaxValue)); //Seed RNG with a random value
 
             _tfsState = Module.Memory.AllocateVariable("TFSTATE", sizeof(ushort));
             _tfspst = Module.Memory.AllocateVariable("TFSPST", FarPtr.Size);
@@ -585,7 +586,6 @@
             switch (ordinal)
             {
                 //Ignored Ordinals
-                case 561: //srand() handled internally
                 case 614: //unfrez -- unlocks video memory, ignored
                 case 174: //DSAIRP
                 case 189: //ENAIRP
@@ -1363,6 +1363,9 @@
                 case 129:
                     cncuid();
                     break;
+                case 561:
+                    srand();
+                    break;
                 default:
                     _logger.Error($"Unknown Exported Function Ordinal in MAJORBBS: {ordinal}:{Ordinals.MAJORBBS[ordinal]}");
                     throw new ArgumentOutOfRangeException($"Unknown Exported Function Ordinal in MAJORBBS: {ordinal}:{Ordinals.MAJORBBS[ordinal]}");
@@ -2344,12 +2347,14 @@
         /// <returns></returns>
         private void rand()
         {
-            var randomValue = _random.Next(1, short.MaxValue);
+            uint multiplier = 0x15A4E35;
+            var seed = Module.Memory.GetDWord("RANDSEED");
+
+            var newSeed = (seed * multiplier) + 1;
 
-#if DEBUG
-            //_logger.Debug($"Generated random number {randomValue} and saved it to AX");
-#endif
-            Registers.AX = (ushort)randomValue;
+            Module.Memory.SetDWord("RANDSEED", newSeed);
+
+            Registers.AX = (ushort)((newSeed >> 16) & 0x7FFF);
         }
 
         /// <summary>
@@ -6078,7 +6083,7 @@
                 {
                     tokenList.Add(Module.Memory.GetString(messagePointer).ToArray());
                 }
                 catch (Exception e)
                 {
                     _logger.Warn($"Error Reading string at {messagePointer}, terminating list at {tokenList.Count} elements");
                     break;
@@ -8334,5 +8339,20 @@
         ///     Returns Pointer to the HDLCON Routine
         /// </summary>
         private ReadOnlySpan<byte> hdlcon => Module.Memory.GetVariablePointer("HDLCON").Data;
+
+        /// <summary>
+        ///     Sets the Seed for the Pseudo-Random Number Generator
+        ///
+        ///     While the seed stored in memory is a 32-bit long, only the lower 16-bits are set
+        ///     via the srand() method. The high 16-bits are always set to zero.
+        ///
+        ///     Signature: void srand(int seed)
+        /// </summary>
+        private void srand()
+        {
+            var randomSeed = GetParameter(0);
+
+            Module.Memory.SetDWord("RANDSEED", randomSeed);
+        }
     }
 }