std.uni: optimize simpleCaseTable

Cuts size of simpleCaseTable entries in half (8 -> 4 bytes), reducing table size from 24 Kb to 12 Kb.
Still only 22 out of 32 bits per entry are actually used, so could be optimized further.
Using plain integers saves 10 ms semantic2 compile time.

std/uni/package.d

@@ -8016,19 +8016,19 @@ if (isInputRange!S1 && isSomeChar!(ElementEncodingType!S1)
             if (idx2 != EMPTY_CASE_TRIE)
             {// both cased chars
                 // adjust idx --> start of bucket
-                idx = idx - sTable[idx].n;
-                idx2 = idx2 - sTable[idx2].n;
+                idx = idx - sTable(idx).n;
+                idx2 = idx2 - sTable(idx2).n;
                 if (idx == idx2)// one bucket, equivalent chars
                     continue;
                 else//  not the same bucket
-                    diff = sTable[idx].ch - sTable[idx2].ch;
+                    diff = sTable(idx).ch - sTable(idx2).ch;
             }
             else
-                diff = sTable[idx - sTable[idx].n].ch - rhs;
+                diff = sTable(idx - sTable(idx).n).ch - rhs;
         }
         else if (idx2 != EMPTY_CASE_TRIE)
         {
-            diff = lhs - sTable[idx2 - sTable[idx2].n].ch;
+            diff = lhs - sTable(idx2 - sTable(idx2).n).ch;
         }
         // one of chars is not cased at all
         return diff;
@@ -8331,7 +8331,7 @@ package(std) auto simpleCaseFoldings(dchar ch) @safe
             {
                 return c;
             }
-            auto ch = sTable[idx].ch;
+            auto ch = sTable(idx).ch;
             return ch;
         }
 
@@ -8367,7 +8367,7 @@ package(std) auto simpleCaseFoldings(dchar ch) @safe
     immutable idx = simpleCaseTrie[ch];
     if (idx == EMPTY_CASE_TRIE)
         return Range(ch);
-    auto entry = sTable[idx];
+    auto entry = sTable(idx);
     immutable start = idx - entry.n;
     return Range(start, entry.size);
 }

tools/unicode_table_generator.d

@@ -117,26 +117,37 @@ struct FullCaseEntry
     }
 }
 
-enum mixedCCEntry = `
+/// 8 byte easy SimpleCaseEntry, will be compressed to SCE which bit packs values to 4 bytes
 struct SimpleCaseEntry
 {
     uint ch;
-    ubyte n, bucket;// n - number in bucket
+    ubyte n; // number in bucket
+    ubyte size;
+    bool isLower;
+    bool isUpper;
+}
 
-pure nothrow @nogc:
+enum mixedCCEntry = `
+/// Simple Case Entry, wrapper around uint to extract bit fields from simpleCaseTable()
+struct SCE
+{
+    uint x;
 
-    @property ubyte size() const
+    nothrow @nogc pure @safe:
+
+    this(uint x)
     {
-        return bucket & 0x3F;
+        this.x = x;
     }
-    @property auto isLower() const
+
+    this(uint ch, ubyte n, ubyte size)
     {
-        return bucket & 0x40;
-    }
-    @property auto isUpper() const
-    {
-        return bucket & 0x80;
+        this.x = ch | n << 20 | size << 24;
     }
+
+    int ch() const { return this.x & 0x1FFFF; }
+    int n() const { return (this.x >> 20) & 0xF; }
+    int size() const { return this.x >> 24; }
 }
 
 /// Bit backed FullCaseEntry
@@ -432,10 +443,13 @@ void loadCaseFolding(string f)
         sort(entry[0 .. size]);
         foreach (i, value; entry[0 .. size])
         {
-            auto withFlags = cast(ubyte) size | (value in lowerCaseSet ? 0x40 : 0)
-                 | (value in upperCaseSet ? 0x80 : 0);
-            simpleTable ~= SimpleCaseEntry(value, cast(ubyte) i,
-                cast(ubyte) withFlags);
+            simpleTable ~= SimpleCaseEntry(
+                value,
+                cast(ubyte) i,
+                cast(ubyte) size,
+                cast(bool) (value in lowerCaseSet),
+                cast(bool) (value in upperCaseSet)
+            );
         }
     }
 
@@ -882,17 +896,22 @@ void writeCaseFolding(File sink)
     {
         write(mixedCCEntry);
 
-        writeln("@property immutable(SimpleCaseEntry[]) simpleCaseTable()");
+        writeln("SCE simpleCaseTable(size_t i)");
         writeln("{");
-        writeln("alias SCE = SimpleCaseEntry;");
-        writeln("static immutable SCE[] t = [");
+        writef("static immutable uint[%d] t = [", simpleTable.length);
         foreach (i, v; simpleTable)
         {
-            writef("SCE(0x%04x, %s, 0x%0x),", v.ch,  v.n, v.bucket);
-            if (i % 4 == 0) writeln();
+            if (i % 8 == 0) writeln();
+            writef("0x%08X,", SCE(v.ch, v.n, v.size).x);
         }
+
+        // Inspect max integer size, so efficient bit packing can be found:
+        stderr.writefln("max n: %X", simpleTable.maxElement!(x => x.n).n); // n: 2-bit
+        stderr.writefln("max ch: %X", simpleTable.maxElement!(x => x.ch).ch); // ch: 17-bit
+        stderr.writefln("max size: %X", simpleTable.maxElement!(x => x.size).size); // size: 3-bit
+
         writeln("];");
-        writeln("return t;");
+        writeln("return SCE(t[i]);");
         writeln("}");
         writeln("@property FCE fullCaseTable(size_t index) nothrow @nogc @safe pure");
         writeln("{");