Add initial big endian support

The largest deterrents to big endian compatibility were:

- In the public API, the unions meant for aliasing and the bit fields:
    - In the case of KeyDownEvent, detecting key presses would become broken. The solution is as simple as reversing the field order in CharScanType.
    - In the case of MessageEvent, reading from 'infoChar', 'infoInt', etc. would not work as expected when the value had been initialized through 'infoPtr', such as when using the 'message' function. It is required to add padding before the non-pointer fields. A concise way of achieving this is by using bit fields. This comes at the expense of not being able to take the address of these fields anymore, but I have found no examples of such usage.
    - In the case of TColorBIOS and TColorRGB, the red and blue components would become swapped. A simple solution is to reorder the bit fields.
- In the internal classes:
    - In TCellChar, the 'moveInt' method does bit-casting, which is fine as long as the parameter itself is the result of bit-casting from a byte array. However, 'moveChar' was implemented with an invocation to 'moveInt', breaking this rule. As a result, none of the single-byte characters that went through 'moveChar' would be displayed.
    - The TermColor and colorconv_r structs, which had manual bit-casting optimizations. This would result in colors not being displayed at all. Rather than changing the struct's layout, in this case it seems more convenient to simply add code to to reverse the casted bytes when necessary.

Some other issues that I found were:

- The internal method 'utf32To8' does bit-casting from an integer to a byte array, so bytes have to be reversed.
- In tvdemo, reversing the mouse buttons would not work because the address of 'TEventQueue::mouseReverse' was being treated as an address to a int32_t, even though it is a Boolean.
- In the far2l terminal extensions, integer values should always be in little-endian format, so bytes have to be reversed.
- The 'AsciiChar' member of 'KEY_EVENT_RECORD' is meant to alias the least significant byte of 'UnicodeChar', so padding has to be added.
- In the internal method 'fast_btoa', a little-endian-dependent optimization has been replaced by an endian-safe one.

The code related to streaming and resource files has not been modified, so files generated in a little endian system may be unreadable in a big endian system and viceversa. This is not so important, though, since it is highly discouraged to use these features.

I also took the oportunity to add tests for several of these points and even a GitHub Actions job to run these tests automatically in a big endian system.

See magiblot/turbo#65.
Fixes #134. Closes #136.

Co-authored-by: MookThompson <58513526+MookThompson@users.noreply.github.com>

.github/workflows/cmake.yml

@@ -2,9 +2,6 @@ name: Build
 
 on: [push, pull_request]
 
-env:
-  BUILD_TYPE: Release
-
 jobs:
   build-linux-gcc:
     name: Linux (GCC) (Unity)
@@ -13,11 +10,11 @@ jobs:
     - uses: actions/checkout@v3
 
     - name: Install Dependencies
-      run: sudo apt -y install libncursesw5-dev libgpm-dev
+      run: sudo apt -y install libncursesw5-dev libgpm-dev libgtest-dev
 
     - name: Configure CMake
       shell: bash
-      run: cmake . -DCMAKE_BUILD_TYPE=$BUILD_TYPE -DTV_REDUCE_APP_SIZE=ON -DTV_LIBRARY_UNITY_BUILD=ON
+      run: cmake . -DCMAKE_BUILD_TYPE=Release -DTV_BUILD_TESTS=ON -DTV_REDUCE_APP_SIZE=ON -DTV_LIBRARY_UNITY_BUILD=ON
 
     - name: Build
       shell: bash
@@ -42,7 +39,7 @@ jobs:
       env:
         CC: gcc-5
         CXX: g++-5
-      run: cmake . -DCMAKE_BUILD_TYPE=$BUILD_TYPE
+      run: cmake . -DCMAKE_BUILD_TYPE=Release
 
     - name: Build
       shell: bash
@@ -62,12 +59,34 @@ jobs:
       env:
         CC: clang
         CXX: clang++
-      run: cmake . -DCMAKE_BUILD_TYPE=$BUILD_TYPE -DTV_OPTIMIZE_BUILD=OFF
+      run: cmake . -DCMAKE_BUILD_TYPE=Release -DTV_OPTIMIZE_BUILD=OFF
 
     - name: Build
       shell: bash
       run: cmake --build . -j$(nproc)
 
+  build-linux-big-endian:
+    name: Linux (GCC) (Big Endian)
+    runs-on: ubuntu-20.04
+    steps:
+    - uses: actions/checkout@v3
+
+    - name: Build in container
+      uses: uraimo/run-on-arch-action@v2
+      with:
+        arch: s390x
+        distro: alpine_latest
+        dockerRunArgs: |
+          --volume "${PWD}:/app"
+        env: |
+          LC_CTYPE: C.UTF-8
+        shell: /bin/sh
+        install: apk update && apk add make cmake g++ ncurses-dev gtest-dev linux-headers
+        run: |
+          cd /app
+          cmake . -DCMAKE_BUILD_TYPE= -DTV_BUILD_USING_GPM=OFF -DTV_BUILD_EXAMPLES=OFF -DTV_BUILD_TESTS=ON -DTV_LIBRARY_UNITY_BUILD=ON
+          cmake --build . -j$(nproc)
+
   build-windows-msvc32:
     name: Windows (MSVC) (Win32)
     runs-on: windows-latest
@@ -160,7 +179,7 @@ jobs:
 
     - name: Configure CMake
       shell: bash
-      run: cmake . -G "MinGW Makefiles" -DCMAKE_BUILD_TYPE=$BUILD_TYPE -DCMAKE_CXX_FLAGS="-static" -DTV_OPTIMIZE_BUILD=OFF
+      run: cmake . -G "MinGW Makefiles" -DCMAKE_BUILD_TYPE= -DCMAKE_CXX_FLAGS="-static" -DTV_LIBRARY_UNITY_BUILD=ON
 
     - name: Build
       shell: bash
@@ -211,7 +230,7 @@ jobs:
 
     - name: Configure CMake
       shell: bash
-      run: cmake . -DCMAKE_BUILD_TYPE=$BUILD_TYPE
+      run: cmake . -DCMAKE_BUILD_TYPE=Release
 
     - name: Build
       shell: bash

examples/tvdemo/tvdemo3.cpp

@@ -48,10 +48,12 @@ void TVDemo::mouse()
 
     if (mouseCage != 0)
         {
+        int32_t mouseReverse = TEventQueue::mouseReverse;
         mouseCage->helpCtx = hcOMMouseDBox;
-        mouseCage->setData(&(TEventQueue::mouseReverse));
+        mouseCage->setData(&mouseReverse);
         if (deskTop->execView(mouseCage) != cmCancel)
-            mouseCage->getData(&(TEventQueue::mouseReverse));
+            mouseCage->getData(&mouseReverse);
+        TEventQueue::mouseReverse = mouseReverse;
         }
     destroy( mouseCage );
 

include/tvision/colors.h

@@ -57,20 +57,34 @@ inline TColorAttr reverseAttribute(TColorAttr attr)
 struct TColorRGB
 {
     uint32_t
+#ifndef TV_BIG_ENDIAN
         b       : 8,
         g       : 8,
         r       : 8,
         _unused : 8;
+#else
+        _unused : 8,
+        r       : 8,
+        g       : 8,
+        b       : 8;
+#endif
 
     TV_TRIVIALLY_CONVERTIBLE(TColorRGB, uint32_t, 0xFFFFFF)
     constexpr inline TColorRGB(uint8_t r, uint8_t g, uint8_t b);
 };
 
 constexpr inline TColorRGB::TColorRGB(uint8_t r, uint8_t g, uint8_t b) :
+#ifndef TV_BIG_ENDIAN
     b(b),
     g(g),
     r(r),
     _unused(0)
+#else
+    _unused(0),
+    r(r),
+    g(g),
+    b(b)
+#endif
 {
 }
 
@@ -90,11 +104,19 @@ constexpr inline TColorRGB::TColorRGB(uint8_t r, uint8_t g, uint8_t b) :
 struct TColorBIOS
 {
     uint8_t
+#ifndef TV_BIG_ENDIAN
         b       : 1,
         g       : 1,
         r       : 1,
         bright  : 1,
         _unused : 4;
+#else
+        _unused : 4,
+        bright  : 1,
+        r       : 1,
+        g       : 1,
+        b       : 1;
+#endif
 
     TV_TRIVIALLY_CONVERTIBLE(TColorBIOS, uint8_t, 0xF)
 };

include/tvision/compat/windows/windows.h

@@ -204,7 +204,11 @@ typedef struct _KEY_EVENT_RECORD {
     WORD wVirtualScanCode;
     union {
         WCHAR UnicodeChar;
+#ifndef TV_BIG_ENDIAN
         CHAR   AsciiChar;
+#else
+        struct { WCHAR : 8*sizeof(WCHAR) - 8, AsciiChar : 8; };
+#endif
     } uChar;
     DWORD dwControlKeyState;
 } KEY_EVENT_RECORD;

include/tvision/internal/ansidisp.h

@@ -5,6 +5,7 @@
 #include <tvision/tv.h>
 
 #include <internal/termdisp.h>
+#include <internal/endian.h>
 
 namespace tvision
 {
@@ -30,6 +31,9 @@ struct TermColor
 
     TermColor& operator=(uint32_t val) noexcept
     {
+#ifdef TV_BIG_ENDIAN
+        reverseBytes(val);
+#endif
         memcpy(this, &val, sizeof(*this));
         return *this;
         static_assert(sizeof(*this) == 4, "");
@@ -38,6 +42,9 @@ struct TermColor
     {
         uint32_t val;
         memcpy(&val, this, sizeof(*this));
+#ifdef TV_BIG_ENDIAN
+        reverseBytes(val);
+#endif
         return val;
     }
     TermColor(uint8_t aIdx, TermColorTypes aType) noexcept

include/tvision/internal/endian.h

@@ -0,0 +1,32 @@
+#ifndef TVISION_ENDIAN_H
+#define TVISION_ENDIAN_H
+
+#include <stdint.h>
+
+namespace tvision
+{
+
+// Optimization: the 'reverseBytes' methods are written in such a way that the
+// compiler will likely replace them with a BSWAP instruction or equivalent.
+
+inline void reverseBytes(uint16_t &val)
+{
+    val = (val << 8) | (val >> 8);
+}
+
+inline void reverseBytes(uint32_t &val)
+{
+    val = ((val << 8) & 0xFF00FF00U) | ((val >> 8) & 0x00FF00FF);
+    val = (val << 16) | (val >> 16);
+}
+
+inline void reverseBytes(uint64_t &val)
+{
+    val = ((val << 8) & 0xFF00FF00FF00FF00ULL) | ((val >> 8) & 0x00FF00FF00FF00FFULL);
+    val = ((val << 16) & 0xFFFF0000FFFF0000ULL) | ((val >> 16) & 0x0000FFFF0000FFFFULL);
+    val = (val << 32) | (val >> 32);
+}
+
+} // namespace tvision
+
+#endif // TVISION_ENDIAN_H

include/tvision/internal/strings.h

@@ -1,19 +1,17 @@
 #ifndef TVISION_STRINGS_H
 #define TVISION_STRINGS_H
 
-#ifndef _TV_VERSION
 #include <tvision/tv.h>
-#endif
 
 namespace tvision
 {
 
 template<class Int>
 inline constexpr Int string_as_int(TStringView s) noexcept
+// CAUTION: It is not endian-safe to reinterpret the result as an array of bytes.
 {
     Int res = 0;
     for (size_t i = 0; i < min(s.size(), sizeof(res)); ++i)
-        // CAUTION: Assumes Little Endian.
         res |= uint64_t(uint8_t(s[i])) << 8*i;
     return res;
 }
@@ -32,15 +30,15 @@ struct alignas(4) btoa_lut_elem_t
 using btoa_lut_t = constarray<btoa_lut_elem_t, 256>;
 
 inline char *fast_btoa(uint8_t value, char *buffer) noexcept
+// Pre: the capacity of 'buffer' is at least 4 bytes.
 {
     extern const btoa_lut_t btoa_lut;
     const auto &lut = (btoa_lut_elem_t (&) [256]) btoa_lut;
-    // CAUTION: Assumes Little Endian.
-    // We can afford to write more bytes into 'buffer' than digits.
-    uint32_t asInt;
-    memcpy(&asInt, &lut[value], 4);
-    memcpy(buffer, &asInt, 4);
-    return buffer + (asInt >> 24);
+    // Optimization: read and write the whole LUT entry at once in order to
+    // minimize memory accesses. We can afford to write more bytes into 'buffer'
+    // than digits.
+    memcpy(buffer, &lut[value], 4);
+    return buffer + (uint8_t) buffer[3];
     static_assert(sizeof(btoa_lut_elem_t) == 4, "");
 }
 

include/tvision/internal/utf8.h

@@ -1,7 +1,9 @@
 #ifndef TVISION_UTF8_H
 #define TVISION_UTF8_H
 
-#include <internal/strings.h>
+#include <tvision/tv.h>
+
+#include <internal/endian.h>
 
 #include <stdint.h>
 #include <string.h>
@@ -66,6 +68,9 @@ inline size_t utf32To8(uint32_t u32, char u8[4]) noexcept
             (( u32        & 0b00111111) | 0b10000000) << 24;
         length = 4;
     }
+#ifdef TV_BIG_ENDIAN
+    reverseBytes(asInt);
+#endif
     memcpy(u8, &asInt, 4);
     return length;
 }

include/tvision/scrncell.h

@@ -76,13 +76,14 @@ struct TCellChar
 
 inline void TCellChar::moveChar(char ch)
 {
-    moveInt((uchar) ch);
+    memset(this, 0, sizeof(*this));
+    _text[0] = ch;
 }
 
 inline void TCellChar::moveInt(uint32_t mbc, bool wide)
+// Pre: 'mbc' is a bit-casted multibyte-encoded character.
 {
     memset(this, 0, sizeof(*this));
-    // CAUTION: Assumes Little Endian.
     memcpy(_text, &mbc, sizeof(mbc));
     _flags = -int(wide) & fWide;
 }

include/tvision/system.h

@@ -187,8 +187,15 @@ inline void TMouse::registerHandler( unsigned mask, void (_FAR *func)() )
 
 struct CharScanType
 {
+#if !defined( TV_BIG_ENDIAN )
     uchar charCode;
     uchar scanCode;
+#else
+    // Due to the reverse byte order, swap the fields in order to preserve
+    // the aliasing with KeyDownEvent::keyCode.
+    uchar scanCode;
+    uchar charCode;
+#endif
 };
 
 struct KeyDownEvent
@@ -222,11 +229,21 @@ struct MessageEvent
     union
         {
         void *infoPtr;
+#if !defined( TV_BIG_ENDIAN )
         int32_t infoLong;
         ushort infoWord;
         short infoInt;
         uchar infoByte;
         char infoChar;
+#else
+        // Due to the reverse byte order, add padding at the beginning to
+        // preserve the aliasing with infoPtr.
+        struct { intptr_t  : 8*sizeof(infoPtr) - 32, infoLong : 32; };
+        struct { uintptr_t : 8*sizeof(infoPtr) - 16, infoWord : 16; };
+        struct { intptr_t  : 8*sizeof(infoPtr) - 16, infoInt  : 16; };
+        struct { uintptr_t : 8*sizeof(infoPtr) - 8,  infoByte : 8;  };
+        struct { intptr_t  : 8*sizeof(infoPtr) - 8,  infoChar : 8;  };
+#endif
         };
 };
 

include/tvision/ttypes.h

@@ -50,6 +50,8 @@ typedef long int32_t;
 typedef uchar uint8_t;
 typedef ushort uint16_t;
 typedef ulong uint32_t;
+typedef long intptr_t;
+typedef ulong uintptr_t;
 #endif
 
 #ifdef __BORLANDC__

source/CMakeLists.txt

@@ -74,6 +74,17 @@ target_compile_definitions(${PROJECT_NAME} PRIVATE
     TVISION_NO_STL
 )
 
+include(TestBigEndian)
+
+TEST_BIG_ENDIAN(IS_BIG_ENDIAN)
+
+if (IS_BIG_ENDIAN)
+    tv_message(STATUS "Big endian system detected")
+    target_compile_definitions(${PROJECT_NAME} PUBLIC
+        TV_BIG_ENDIAN
+    )
+endif()
+
 # Dependencies
 
 if (NOT WIN32)
@@ -172,6 +183,7 @@ if (CMAKE_VERSION VERSION_GREATER_EQUAL "3.16.0" AND TV_OPTIMIZE_BUILD)
         file(GLOB_RECURSE TVSOURCE_NOUNITY "${CMAKE_CURRENT_LIST_DIR}/tvision/s*.cpp")
         list(APPEND TVSOURCE_NOUNITY "${CMAKE_CURRENT_LIST_DIR}/tvision/new.cpp")
         list(REMOVE_ITEM TVSOURCE_NOUNITY
+            "${CMAKE_CURRENT_LIST_DIR}/tvision/snprintf.cpp"
             "${CMAKE_CURRENT_LIST_DIR}/tvision/stddlg.cpp"
             "${CMAKE_CURRENT_LIST_DIR}/tvision/strmstat.cpp"
             "${CMAKE_CURRENT_LIST_DIR}/tvision/syserr.cpp"

source/platform/ansidisp.cpp

@@ -158,7 +158,11 @@ struct alignas(8) colorconv_r
     colorconv_r() = default;
     colorconv_r(TermColor aColor, TColorAttr::Style aExtraFlags=0) noexcept
     {
+        // Optimization: do bit-casting manually, just like with TermColor.
         uint64_t val = aColor | (uint64_t(aExtraFlags) << 32);
+#ifdef TV_BIG_ENDIAN
+        reverseBytes(val);
+#endif
         memcpy(this, &val, 8);
         static_assert(sizeof(*this) == 8, "");
     }