Raise TCellChar size to 12

After some testing I have found Wikipedia articles where 8 bytes were not enough to fit all the diacritics in one cell. So I raised it to 12 bytes, where at least 2 combining characters can fit in the worst case. This should be enough for most real-world, natural language use cases. I don't care about zalgo.

12 bytes and alignas(4) is still a sweet spot for performance where most operations (including comparison) can be carried out in registers. It also preserves sizeof(TScreenCell) == 16, although that struct is likely to become larger in the future if true color support is added.

See #26.

include/tvision/scrncell.h

@@ -176,12 +176,44 @@ struct TScreenCellA : trivially_convertible<uint16_t>
 
 };
 
-struct TCellChar : trivially_convertible<uint64_t>
+struct alignas(4) TCellChar
 {
 
-    uint8_t bytes[8];
+    uint8_t bytes[12];
 
-    using trivially_convertible::trivially_convertible;
+    TCellChar() = default;
+
+    TCellChar(uint64_t ch)
+    {
+        *this = ch;
+    }
+
+    TCellChar& operator=(uint64_t ch)
+    {
+        memset(this, 0, sizeof(*this));
+        memcpy(bytes, &ch, std::min(sizeof(bytes), sizeof(ch)));
+        return *this;
+    }
+
+    bool operator==(TCellChar other) const
+    {
+        return memcmp(bytes, other.bytes, sizeof(bytes)) == 0;
+    }
+
+    bool operator!=(TCellChar other) const
+    {
+        return !(*this == other);
+    }
+
+    uint8_t& operator[](size_t i)
+    {
+        return bytes[i];
+    }
+
+    const uint8_t& operator[](size_t i) const
+    {
+        return bytes[i];
+    }
 
     void append(TStringView text)
     {
@@ -204,7 +236,7 @@ struct TCellChar : trivially_convertible<uint64_t>
 
     static constexpr void check_assumptions()
     {
-        check_trivial<TCellChar>();
+        static_assert(std::is_trivial<TCellChar>());
     }
 
 };

source/platform/buffdisp.cpp

@@ -171,11 +171,13 @@ void BufferedDisplay::onScreenResize()
 void BufferedDisplay::ensurePrintable(BufferCell &cell) const
 {
     auto &ch = cell.Char;
-    if (ch == '\0')
-        ch = ' ';
-    else if (ch < ' ' || (0x7F <= ch && ch < 0x100)) {
-        // Translate from codepage as fallback.
-        ch = CpTranslator::toUtf8Int(ch);
+    if (!ch[1]) /* size 1 */ {
+        auto &c = ch[0];
+        if (c == '\0')
+            c = ' ';
+        else if (c < ' ' || 0x7F <= c)
+            // Translate from codepage as fallback.
+            ch = CpTranslator::toUtf8Int(c);
     } else if (ch == TScreenCell::wideCharTrail) {
         ch = widePlaceholder;
         cell.extraWidth = 0;