From 27459d0e400bc7c157a6f870801d9650609970e8 Mon Sep 17 00:00:00 2001
From: "Eric P. Nusbaum" <eric@enusbaum.com>
Date: Sat, 30 Dec 2023 11:54:43 -0500
Subject: [PATCH] Fix for SKPWRD

- Fixes a bug with `SKPWRD` where it wouldn't properly skip a word where the final character (`/0`) was at offer `0xFFFF`
- Added Unit Tests to `skpwrd_Tests.cs` to test for this specific scenario
---
 .../ExportedModules/ExportedModuleTestBase.cs |  8 ++--
 .../ExportedModules/Majorbbs/skpwrd_Tests.cs  | 37 +++++++++++++++++++
 .../HostProcess/ExportedModules/Majorbbs.cs   |  2 +-
 3 files changed, 43 insertions(+), 4 deletions(-)

diff --git a/MBBSEmu.Tests/ExportedModules/ExportedModuleTestBase.cs b/MBBSEmu.Tests/ExportedModules/ExportedModuleTestBase.cs
index 6aaf0773..23122e00 100644
--- a/MBBSEmu.Tests/ExportedModules/ExportedModuleTestBase.cs
+++ b/MBBSEmu.Tests/ExportedModules/ExportedModuleTestBase.cs
@@ -23,9 +23,11 @@ namespace MBBSEmu.Tests.ExportedModules
 {
     public abstract class ExportedModuleTestBase : TestBase, IDisposable
     {
-        // list of ordinals that use the __stdcall convention, which means the callee cleans up the
-        // stack.
-        // __cdecl convention has the caller cleaning up the stack.
+        /// <summary>
+        ///     List of ordinals that use the __stdcall convention, which means the callee cleans up the stack.
+        ///
+        ///     __cdecl convention has the caller cleaning up the stack.
+        /// </summary>
         private static readonly HashSet<ushort> STDCALL_ORDINALS = new HashSet<ushort> {
             654, // f_ldiv
             656, // f_ludiv
diff --git a/MBBSEmu.Tests/ExportedModules/Majorbbs/skpwrd_Tests.cs b/MBBSEmu.Tests/ExportedModules/Majorbbs/skpwrd_Tests.cs
index 5f030337..509721b4 100644
--- a/MBBSEmu.Tests/ExportedModules/Majorbbs/skpwrd_Tests.cs
+++ b/MBBSEmu.Tests/ExportedModules/Majorbbs/skpwrd_Tests.cs
@@ -33,5 +33,42 @@ public void SKPWRD_Test(string inputString, string expectedString)
                 Encoding.ASCII.GetString(
                     mbbsEmuMemoryCore.GetString(mbbsEmuCpuRegisters.GetPointer())));
         }
+
+        /// <summary>
+        ///     These tests are to verify a specific scenario where the final character of the string being parsed
+        ///     is at the last offset in a segment (0xFFFF)
+        /// </summary>
+        /// <param name="inputString"></param>
+        /// <param name="expectedString"></param>
+        [Theory]
+        [InlineData("TEST TEST\0", " TEST\0")]
+        [InlineData("TEST\0", "\0")]
+        [InlineData("\0", "\0")]
+        public void SKPWRD_Test_EndOfSegment(string inputString, string expectedString)
+        {
+            //Reset State
+            Reset();
+
+            //Set Argument Values to be Passed In
+            var stringPointer = mbbsEmuMemoryCore.AllocateVariable("INPUT_STRING", (ushort)(inputString.Length + 1));
+
+            //Ensure Input String ends in \0
+            if (inputString[^1] != '\0')
+                inputString += '\0';
+
+            //This will change the final character of the string (\0) to be at 0xFFFF
+            stringPointer.Offset = (ushort)(0x10000 - inputString.Length);
+
+            //Get the Segment and we'll allocate this at the end
+            mbbsEmuMemoryCore.SetArray(stringPointer, Encoding.ASCII.GetBytes(inputString));
+
+            //Execute Test
+            ExecuteApiTest(HostProcess.ExportedModules.Majorbbs.Segment, SKPWRD_ORDINAL, new List<FarPtr> { stringPointer });
+
+            //Verify Results
+            Assert.Equal(expectedString,
+                Encoding.ASCII.GetString(
+                    mbbsEmuMemoryCore.GetString(mbbsEmuCpuRegisters.GetPointer())));
+        }
     }
 }
diff --git a/MBBSEmu/HostProcess/ExportedModules/Majorbbs.cs b/MBBSEmu/HostProcess/ExportedModules/Majorbbs.cs
index c0601364..7a99b0b9 100644
--- a/MBBSEmu/HostProcess/ExportedModules/Majorbbs.cs
+++ b/MBBSEmu/HostProcess/ExportedModules/Majorbbs.cs
@@ -7212,7 +7212,7 @@ private void skpwrd()
         {
             var stringPointerBase = GetParameterPointer(0);
 
-            for (var i = stringPointerBase.Offset; i < ushort.MaxValue; i++)
+            for (var i = stringPointerBase.Offset; i <= ushort.MaxValue; i++)
             {
                 var currentCharacter = Module.Memory.GetByte(stringPointerBase.Segment, i);
                 if (currentCharacter != 0 && currentCharacter != ' ') continue;